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data-event-name="pinnable-header.vector-toc.pin">move to sidebar</button> <button class="vector-pinnable-header-toggle-button vector-pinnable-header-unpin-button" data-event-name="pinnable-header.vector-toc.unpin">hide</button> </div> <ul class="vector-toc-contents" id="mw-panel-toc-list"> <li id="toc-mw-content-text" class="vector-toc-list-item vector-toc-level-1"> <a href="#" class="vector-toc-link"> <div class="vector-toc-text">(Top)</div> </a> </li> <li id="toc-History" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#History"> <div class="vector-toc-text"> <span class="vector-toc-numb">1</span> <span>History</span> </div> </a> <ul id="toc-History-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Definition" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Definition"> <div class="vector-toc-text"> <span class="vector-toc-numb">2</span> <span>Definition</span> </div> </a> <button aria-controls="toc-Definition-sublist" class="cdx-button cdx-button--weight-quiet cdx-button--icon-only vector-toc-toggle"> <span class="vector-icon mw-ui-icon-wikimedia-expand"></span> <span>Toggle Definition subsection</span> </button> <ul id="toc-Definition-sublist" class="vector-toc-list"> <li id="toc-pH" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#pH"> <div class="vector-toc-text"> <span class="vector-toc-numb">2.1</span> <span>pH</span> </div> </a> <ul id="toc-pH-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-p[H]" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#p[H]"> <div class="vector-toc-text"> <span class="vector-toc-numb">2.2</span> <span>p[H]</span> </div> </a> <ul id="toc-p[H]-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-pOH" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#pOH"> <div class="vector-toc-text"> <span class="vector-toc-numb">2.3</span> <span>pOH</span> </div> </a> <ul id="toc-pOH-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Measurement" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Measurement"> <div class="vector-toc-text"> <span class="vector-toc-numb">3</span> <span>Measurement</span> </div> </a> <button aria-controls="toc-Measurement-sublist" class="cdx-button cdx-button--weight-quiet cdx-button--icon-only vector-toc-toggle"> <span class="vector-icon mw-ui-icon-wikimedia-expand"></span> <span>Toggle Measurement subsection</span> </button> <ul id="toc-Measurement-sublist" class="vector-toc-list"> <li id="toc-pH_Indicators" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#pH_Indicators"> <div class="vector-toc-text"> <span class="vector-toc-numb">3.1</span> <span>pH Indicators</span> </div> </a> <ul id="toc-pH_Indicators-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Non-aqueous_solutions" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Non-aqueous_solutions"> <div class="vector-toc-text"> <span class="vector-toc-numb">3.2</span> <span>Non-aqueous solutions</span> </div> </a> <ul id="toc-Non-aqueous_solutions-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Unified_absolute_pH_scale" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Unified_absolute_pH_scale"> <div class="vector-toc-text"> <span class="vector-toc-numb">3.3</span> <span>Unified absolute pH scale</span> </div> </a> <ul id="toc-Unified_absolute_pH_scale-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Extremes_of_pH_measurements" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Extremes_of_pH_measurements"> <div class="vector-toc-text"> <span class="vector-toc-numb">3.4</span> <span>Extremes of pH measurements</span> </div> </a> <ul id="toc-Extremes_of_pH_measurements-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Applications" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Applications"> <div class="vector-toc-text"> <span class="vector-toc-numb">4</span> <span>Applications</span> </div> </a> <button aria-controls="toc-Applications-sublist" class="cdx-button cdx-button--weight-quiet cdx-button--icon-only vector-toc-toggle"> <span class="vector-icon mw-ui-icon-wikimedia-expand"></span> <span>Toggle Applications subsection</span> </button> <ul id="toc-Applications-sublist" class="vector-toc-list"> <li id="toc-pH_in_soil" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#pH_in_soil"> <div class="vector-toc-text"> <span class="vector-toc-numb">4.1</span> <span>pH in soil</span> </div> </a> <ul id="toc-pH_in_soil-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-pH_in_plants" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#pH_in_plants"> <div class="vector-toc-text"> <span class="vector-toc-numb">4.2</span> <span>pH in plants</span> </div> </a> <ul id="toc-pH_in_plants-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-pH_in_the_ocean" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#pH_in_the_ocean"> <div class="vector-toc-text"> <span class="vector-toc-numb">4.3</span> <span>pH in the ocean</span> </div> </a> <ul id="toc-pH_in_the_ocean-sublist" class="vector-toc-list"> <li id="toc-Three_pH_scales_in_oceanography" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#Three_pH_scales_in_oceanography"> <div class="vector-toc-text"> <span class="vector-toc-numb">4.3.1</span> <span>Three pH scales in oceanography</span> </div> </a> <ul id="toc-Three_pH_scales_in_oceanography-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-pH_in_food" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#pH_in_food"> <div class="vector-toc-text"> <span class="vector-toc-numb">4.4</span> <span>pH in food</span> </div> </a> <ul id="toc-pH_in_food-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-pH_of_various_body_fluids" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#pH_of_various_body_fluids"> <div class="vector-toc-text"> <span class="vector-toc-numb">4.5</span> <span>pH of various body fluids</span> </div> </a> <ul id="toc-pH_of_various_body_fluids-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-pH_calculations" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#pH_calculations"> <div class="vector-toc-text"> <span class="vector-toc-numb">5</span> <span>pH calculations</span> </div> </a> <button aria-controls="toc-pH_calculations-sublist" class="cdx-button cdx-button--weight-quiet cdx-button--icon-only vector-toc-toggle"> <span class="vector-icon mw-ui-icon-wikimedia-expand"></span> <span>Toggle pH calculations subsection</span> </button> <ul id="toc-pH_calculations-sublist" class="vector-toc-list"> <li id="toc-Strong_acids_and_bases" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Strong_acids_and_bases"> <div class="vector-toc-text"> <span class="vector-toc-numb">5.1</span> <span>Strong acids and bases</span> </div> </a> <ul id="toc-Strong_acids_and_bases-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Weak_acids_and_bases" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Weak_acids_and_bases"> <div class="vector-toc-text"> <span class="vector-toc-numb">5.2</span> <span>Weak acids and bases</span> </div> </a> <ul id="toc-Weak_acids_and_bases-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-General_method" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#General_method"> <div class="vector-toc-text"> <span class="vector-toc-numb">5.3</span> <span>General method</span> </div> </a> <ul id="toc-General_method-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-See_also" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#See_also"> <div class="vector-toc-text"> <span class="vector-toc-numb">6</span> <span>See also</span> </div> </a> <ul id="toc-See_also-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-References" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#References"> <div class="vector-toc-text"> <span class="vector-toc-numb">7</span> <span>References</span> </div> </a> <ul id="toc-References-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-External_links" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#External_links"> <div class="vector-toc-text"> <span class="vector-toc-numb">8</span> <span>External links</span> </div> </a> <ul id="toc-External_links-sublist" class="vector-toc-list"> </ul> </li> </ul> </div> </div> </nav> </div> </div> <div class="mw-content-container"> <main id="content" class="mw-body"> <header class="mw-body-header vector-page-titlebar"> <nav aria-label="Contents" class="vector-toc-landmark"> <div id="vector-page-titlebar-toc" class="vector-dropdown vector-page-titlebar-toc vector-button-flush-left" title="Table of Contents" > <input type="checkbox" id="vector-page-titlebar-toc-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-vector-page-titlebar-toc" class="vector-dropdown-checkbox " aria-label="Toggle the table of contents" > <label id="vector-page-titlebar-toc-label" for="vector-page-titlebar-toc-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--icon-only " aria-hidden="true" ><span class="vector-icon mw-ui-icon-listBullet mw-ui-icon-wikimedia-listBullet"></span> <span class="vector-dropdown-label-text">Toggle the table of contents</span> </label> <div class="vector-dropdown-content"> <div id="vector-page-titlebar-toc-unpinned-container" class="vector-unpinned-container"> </div> </div> </div> </nav> <h1 id="firstHeading" class="firstHeading mw-first-heading">pH</h1> <div id="p-lang-btn" class="vector-dropdown mw-portlet mw-portlet-lang" > <input type="checkbox" id="p-lang-btn-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-p-lang-btn" class="vector-dropdown-checkbox mw-interlanguage-selector" aria-label="Go to an article in another language. Available in 104 languages" > <label id="p-lang-btn-label" for="p-lang-btn-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--action-progressive mw-portlet-lang-heading-104" aria-hidden="true" ><span class="vector-icon mw-ui-icon-language-progressive mw-ui-icon-wikimedia-language-progressive"></span> <span class="vector-dropdown-label-text">104 languages</span> </label> <div class="vector-dropdown-content"> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li class="interlanguage-link interwiki-af mw-list-item"><a href="https://af.wikipedia.org/wiki/PH" title="PH – Afrikaans" lang="af" hreflang="af" data-title="PH" data-language-autonym="Afrikaans" data-language-local-name="Afrikaans" class="interlanguage-link-target"><span>Afrikaans</span></a></li><li class="interlanguage-link interwiki-als mw-list-item"><a href="https://als.wikipedia.org/wiki/PH-Wert" title="PH-Wert – Alemannic" lang="gsw" hreflang="gsw" data-title="PH-Wert" data-language-autonym="Alemannisch" data-language-local-name="Alemannic" class="interlanguage-link-target"><span>Alemannisch</span></a></li><li class="interlanguage-link interwiki-anp mw-list-item"><a href="https://anp.wikipedia.org/wiki/%E0%A4%AA%E0%A5%80%E0%A4%8F%E0%A4%9A_%E0%A4%AE%E0%A4%BE%E0%A4%A8" title="पीएच मान – Angika" lang="anp" hreflang="anp" data-title="पीएच मान" data-language-autonym="अंगिका" data-language-local-name="Angika" class="interlanguage-link-target"><span>अंगिका</span></a></li><li class="interlanguage-link interwiki-ar mw-list-item"><a href="https://ar.wikipedia.org/wiki/%D8%A3%D8%B3_%D9%87%D9%8A%D8%AF%D8%B1%D9%88%D8%AC%D9%8A%D9%86%D9%8A" title="أس هيدروجيني – Arabic" lang="ar" hreflang="ar" data-title="أس هيدروجيني" data-language-autonym="العربية" data-language-local-name="Arabic" class="interlanguage-link-target"><span>العربية</span></a></li><li class="interlanguage-link interwiki-ast mw-list-item"><a href="https://ast.wikipedia.org/wiki/PH" title="PH – Asturian" lang="ast" hreflang="ast" data-title="PH" data-language-autonym="Asturianu" data-language-local-name="Asturian" class="interlanguage-link-target"><span>Asturianu</span></a></li><li class="interlanguage-link interwiki-az mw-list-item"><a href="https://az.wikipedia.org/wiki/PH" title="PH – Azerbaijani" lang="az" hreflang="az" data-title="PH" data-language-autonym="Azərbaycanca" data-language-local-name="Azerbaijani" class="interlanguage-link-target"><span>Azərbaycanca</span></a></li><li class="interlanguage-link interwiki-bn mw-list-item"><a href="https://bn.wikipedia.org/wiki/%E0%A6%AA%E0%A6%BF%E0%A6%8F%E0%A6%87%E0%A6%9A" title="পিএইচ – Bangla" lang="bn" hreflang="bn" data-title="পিএইচ" data-language-autonym="বাংলা" data-language-local-name="Bangla" class="interlanguage-link-target"><span>বাংলা</span></a></li><li class="interlanguage-link interwiki-zh-min-nan mw-list-item"><a href="https://zh-min-nan.wikipedia.org/wiki/PH" title="PH – Minnan" lang="nan" hreflang="nan" data-title="PH" data-language-autonym="閩南語 / Bân-lâm-gú" data-language-local-name="Minnan" class="interlanguage-link-target"><span>閩南語 / Bân-lâm-gú</span></a></li><li class="interlanguage-link interwiki-be mw-list-item"><a href="https://be.wikipedia.org/wiki/%D0%92%D0%B0%D0%B4%D0%B0%D1%80%D0%BE%D0%B4%D0%BD%D1%8B_%D0%BF%D0%B0%D0%BA%D0%B0%D0%B7%D1%87%D1%8B%D0%BA" title="Вадародны паказчык – Belarusian" lang="be" hreflang="be" data-title="Вадародны паказчык" data-language-autonym="Беларуская" data-language-local-name="Belarusian" class="interlanguage-link-target"><span>Беларуская</span></a></li><li class="interlanguage-link interwiki-bh mw-list-item"><a href="https://bh.wikipedia.org/wiki/%E0%A4%AA%E0%A5%80%E0%A4%8F%E0%A4%9A" title="पीएच – Bhojpuri" lang="bh" hreflang="bh" data-title="पीएच" data-language-autonym="भोजपुरी" data-language-local-name="Bhojpuri" class="interlanguage-link-target"><span>भोजपुरी</span></a></li><li class="interlanguage-link interwiki-bcl mw-list-item"><a href="https://bcl.wikipedia.org/wiki/PH" title="PH – Central Bikol" lang="bcl" hreflang="bcl" data-title="PH" data-language-autonym="Bikol Central" data-language-local-name="Central Bikol" class="interlanguage-link-target"><span>Bikol Central</span></a></li><li class="interlanguage-link interwiki-bg mw-list-item"><a href="https://bg.wikipedia.org/wiki/%D0%92%D0%BE%D0%B4%D0%BE%D1%80%D0%BE%D0%B4%D0%B5%D0%BD_%D0%BF%D0%BE%D0%BA%D0%B0%D0%B7%D0%B0%D1%82%D0%B5%D0%BB" title="Водороден показател – Bulgarian" lang="bg" hreflang="bg" data-title="Водороден показател" data-language-autonym="Български" data-language-local-name="Bulgarian" class="interlanguage-link-target"><span>Български</span></a></li><li class="interlanguage-link interwiki-bs mw-list-item"><a href="https://bs.wikipedia.org/wiki/PH" title="PH – Bosnian" lang="bs" hreflang="bs" data-title="PH" data-language-autonym="Bosanski" data-language-local-name="Bosnian" class="interlanguage-link-target"><span>Bosanski</span></a></li><li class="interlanguage-link interwiki-ca mw-list-item"><a href="https://ca.wikipedia.org/wiki/PH" title="PH – Catalan" lang="ca" hreflang="ca" data-title="PH" data-language-autonym="Català" data-language-local-name="Catalan" class="interlanguage-link-target"><span>Català</span></a></li><li class="interlanguage-link interwiki-cs mw-list-item"><a href="https://cs.wikipedia.org/wiki/PH" title="PH – Czech" lang="cs" hreflang="cs" data-title="PH" data-language-autonym="Čeština" data-language-local-name="Czech" class="interlanguage-link-target"><span>Čeština</span></a></li><li class="interlanguage-link interwiki-cy mw-list-item"><a href="https://cy.wikipedia.org/wiki/PH" title="PH – Welsh" lang="cy" hreflang="cy" data-title="PH" data-language-autonym="Cymraeg" data-language-local-name="Welsh" class="interlanguage-link-target"><span>Cymraeg</span></a></li><li class="interlanguage-link interwiki-da mw-list-item"><a href="https://da.wikipedia.org/wiki/PH" title="PH – Danish" lang="da" hreflang="da" data-title="PH" data-language-autonym="Dansk" data-language-local-name="Danish" class="interlanguage-link-target"><span>Dansk</span></a></li><li class="interlanguage-link interwiki-se mw-list-item"><a href="https://se.wikipedia.org/wiki/PH" title="PH – Northern Sami" lang="se" hreflang="se" data-title="PH" data-language-autonym="Davvisámegiella" data-language-local-name="Northern Sami" class="interlanguage-link-target"><span>Davvisámegiella</span></a></li><li class="interlanguage-link interwiki-de mw-list-item"><a href="https://de.wikipedia.org/wiki/PH-Wert" title="PH-Wert – German" lang="de" hreflang="de" data-title="PH-Wert" data-language-autonym="Deutsch" data-language-local-name="German" class="interlanguage-link-target"><span>Deutsch</span></a></li><li class="interlanguage-link interwiki-et mw-list-item"><a href="https://et.wikipedia.org/wiki/Vesinikueksponent" title="Vesinikueksponent – Estonian" lang="et" hreflang="et" data-title="Vesinikueksponent" data-language-autonym="Eesti" data-language-local-name="Estonian" class="interlanguage-link-target"><span>Eesti</span></a></li><li class="interlanguage-link interwiki-el mw-list-item"><a href="https://el.wikipedia.org/wiki/PH" title="PH – Greek" lang="el" hreflang="el" data-title="PH" data-language-autonym="Ελληνικά" data-language-local-name="Greek" class="interlanguage-link-target"><span>Ελληνικά</span></a></li><li class="interlanguage-link interwiki-es mw-list-item"><a href="https://es.wikipedia.org/wiki/PH" title="PH – Spanish" lang="es" hreflang="es" data-title="PH" data-language-autonym="Español" data-language-local-name="Spanish" class="interlanguage-link-target"><span>Español</span></a></li><li class="interlanguage-link interwiki-eo mw-list-item"><a href="https://eo.wikipedia.org/wiki/PH_(kemia_parametro)" title="PH (kemia parametro) – Esperanto" lang="eo" hreflang="eo" data-title="PH (kemia parametro)" data-language-autonym="Esperanto" data-language-local-name="Esperanto" class="interlanguage-link-target"><span>Esperanto</span></a></li><li class="interlanguage-link interwiki-eu mw-list-item"><a href="https://eu.wikipedia.org/wiki/PH" title="PH – Basque" lang="eu" hreflang="eu" data-title="PH" data-language-autonym="Euskara" data-language-local-name="Basque" class="interlanguage-link-target"><span>Euskara</span></a></li><li class="interlanguage-link interwiki-fa mw-list-item"><a href="https://fa.wikipedia.org/wiki/%D9%BE%DB%8C%E2%80%8C%D8%A7%DA%86" title="پی‌اچ – Persian" lang="fa" hreflang="fa" data-title="پی‌اچ" data-language-autonym="فارسی" data-language-local-name="Persian" class="interlanguage-link-target"><span>فارسی</span></a></li><li class="interlanguage-link interwiki-fr mw-list-item"><a href="https://fr.wikipedia.org/wiki/Potentiel_hydrog%C3%A8ne" title="Potentiel hydrogène – French" lang="fr" hreflang="fr" data-title="Potentiel hydrogène" data-language-autonym="Français" data-language-local-name="French" class="interlanguage-link-target"><span>Français</span></a></li><li class="interlanguage-link interwiki-ga mw-list-item"><a href="https://ga.wikipedia.org/wiki/PH" title="PH – Irish" lang="ga" hreflang="ga" data-title="PH" data-language-autonym="Gaeilge" data-language-local-name="Irish" class="interlanguage-link-target"><span>Gaeilge</span></a></li><li class="interlanguage-link interwiki-gl mw-list-item"><a href="https://gl.wikipedia.org/wiki/PH" title="PH – Galician" lang="gl" hreflang="gl" data-title="PH" data-language-autonym="Galego" data-language-local-name="Galician" class="interlanguage-link-target"><span>Galego</span></a></li><li class="interlanguage-link interwiki-hak mw-list-item"><a href="https://hak.wikipedia.org/wiki/PH" title="PH – Hakka Chinese" lang="hak" hreflang="hak" data-title="PH" data-language-autonym="客家語 / Hak-kâ-ngî" data-language-local-name="Hakka Chinese" class="interlanguage-link-target"><span>客家語 / Hak-kâ-ngî</span></a></li><li class="interlanguage-link interwiki-ko mw-list-item"><a href="https://ko.wikipedia.org/wiki/%EC%88%98%EC%86%8C_%EC%9D%B4%EC%98%A8_%EB%86%8D%EB%8F%84_%EC%A7%80%EC%88%98" title="수소 이온 농도 지수 – Korean" lang="ko" hreflang="ko" data-title="수소 이온 농도 지수" data-language-autonym="한국어" data-language-local-name="Korean" class="interlanguage-link-target"><span>한국어</span></a></li><li class="interlanguage-link interwiki-hy mw-list-item"><a href="https://hy.wikipedia.org/wiki/%D5%8B%D6%80%D5%A1%D5%AE%D5%B6%D5%A1%D5%B5%D5%AB%D5%B6_%D6%81%D5%B8%D6%82%D6%81%D5%AB%D5%B9" title="Ջրածնային ցուցիչ – Armenian" lang="hy" hreflang="hy" data-title="Ջրածնային ցուցիչ" data-language-autonym="Հայերեն" data-language-local-name="Armenian" class="interlanguage-link-target"><span>Հայերեն</span></a></li><li class="interlanguage-link interwiki-hi mw-list-item"><a href="https://hi.wikipedia.org/wiki/PH" title="PH – Hindi" lang="hi" hreflang="hi" data-title="PH" data-language-autonym="हिन्दी" data-language-local-name="Hindi" class="interlanguage-link-target"><span>हिन्दी</span></a></li><li class="interlanguage-link interwiki-hr mw-list-item"><a href="https://hr.wikipedia.org/wiki/PH" title="PH – Croatian" lang="hr" hreflang="hr" data-title="PH" data-language-autonym="Hrvatski" data-language-local-name="Croatian" class="interlanguage-link-target"><span>Hrvatski</span></a></li><li class="interlanguage-link interwiki-io mw-list-item"><a href="https://io.wikipedia.org/wiki/PH" title="PH – Ido" lang="io" hreflang="io" data-title="PH" data-language-autonym="Ido" data-language-local-name="Ido" class="interlanguage-link-target"><span>Ido</span></a></li><li class="interlanguage-link interwiki-id mw-list-item"><a href="https://id.wikipedia.org/wiki/PH" title="PH – Indonesian" lang="id" hreflang="id" data-title="PH" data-language-autonym="Bahasa Indonesia" data-language-local-name="Indonesian" class="interlanguage-link-target"><span>Bahasa Indonesia</span></a></li><li class="interlanguage-link interwiki-ia mw-list-item"><a href="https://ia.wikipedia.org/wiki/Potential_de_hydrogeno" title="Potential de hydrogeno – Interlingua" lang="ia" hreflang="ia" data-title="Potential de hydrogeno" data-language-autonym="Interlingua" data-language-local-name="Interlingua" class="interlanguage-link-target"><span>Interlingua</span></a></li><li class="interlanguage-link interwiki-is mw-list-item"><a href="https://is.wikipedia.org/wiki/S%C3%BDrustig" title="Sýrustig – Icelandic" lang="is" hreflang="is" data-title="Sýrustig" data-language-autonym="Íslenska" data-language-local-name="Icelandic" class="interlanguage-link-target"><span>Íslenska</span></a></li><li class="interlanguage-link interwiki-it mw-list-item"><a href="https://it.wikipedia.org/wiki/PH" title="PH – Italian" lang="it" hreflang="it" data-title="PH" data-language-autonym="Italiano" data-language-local-name="Italian" class="interlanguage-link-target"><span>Italiano</span></a></li><li class="interlanguage-link interwiki-he mw-list-item"><a href="https://he.wikipedia.org/wiki/PH" title="PH – Hebrew" lang="he" hreflang="he" data-title="PH" data-language-autonym="עברית" data-language-local-name="Hebrew" class="interlanguage-link-target"><span>עברית</span></a></li><li class="interlanguage-link interwiki-jv mw-list-item"><a href="https://jv.wikipedia.org/wiki/PH" title="PH – Javanese" lang="jv" hreflang="jv" data-title="PH" data-language-autonym="Jawa" data-language-local-name="Javanese" class="interlanguage-link-target"><span>Jawa</span></a></li><li class="interlanguage-link interwiki-kbp mw-list-item"><a href="https://kbp.wikipedia.org/wiki/PH" title="PH – Kabiye" lang="kbp" hreflang="kbp" data-title="PH" data-language-autonym="Kabɩyɛ" data-language-local-name="Kabiye" class="interlanguage-link-target"><span>Kabɩyɛ</span></a></li><li class="interlanguage-link interwiki-kn mw-list-item"><a href="https://kn.wikipedia.org/wiki/%E0%B2%AA%E0%B2%BF_%E0%B2%B9%E0%B3%86%E0%B2%9A%E0%B3%8D" title="ಪಿ ಹೆಚ್ – Kannada" lang="kn" hreflang="kn" data-title="ಪಿ ಹೆಚ್" data-language-autonym="ಕನ್ನಡ" data-language-local-name="Kannada" class="interlanguage-link-target"><span>ಕನ್ನಡ</span></a></li><li class="interlanguage-link interwiki-pam mw-list-item"><a href="https://pam.wikipedia.org/wiki/PH" title="PH – Pampanga" lang="pam" hreflang="pam" data-title="PH" data-language-autonym="Kapampangan" data-language-local-name="Pampanga" class="interlanguage-link-target"><span>Kapampangan</span></a></li><li class="interlanguage-link interwiki-ka mw-list-item"><a href="https://ka.wikipedia.org/wiki/PH" title="PH – Georgian" lang="ka" hreflang="ka" data-title="PH" data-language-autonym="ქართული" data-language-local-name="Georgian" class="interlanguage-link-target"><span>ქართული</span></a></li><li class="interlanguage-link interwiki-kk mw-list-item"><a href="https://kk.wikipedia.org/wiki/PH" title="PH – Kazakh" lang="kk" hreflang="kk" data-title="PH" data-language-autonym="Қазақша" data-language-local-name="Kazakh" class="interlanguage-link-target"><span>Қазақша</span></a></li><li class="interlanguage-link interwiki-sw mw-list-item"><a href="https://sw.wikipedia.org/wiki/Thamani_pH" title="Thamani pH – Swahili" lang="sw" hreflang="sw" data-title="Thamani pH" data-language-autonym="Kiswahili" data-language-local-name="Swahili" class="interlanguage-link-target"><span>Kiswahili</span></a></li><li class="interlanguage-link interwiki-ht mw-list-item"><a href="https://ht.wikipedia.org/wiki/PH" title="PH – Haitian Creole" lang="ht" hreflang="ht" data-title="PH" data-language-autonym="Kreyòl ayisyen" data-language-local-name="Haitian Creole" class="interlanguage-link-target"><span>Kreyòl ayisyen</span></a></li><li class="interlanguage-link interwiki-ku mw-list-item"><a href="https://ku.wikipedia.org/wiki/Nirxa_pH" title="Nirxa pH – Kurdish" lang="ku" hreflang="ku" data-title="Nirxa pH" data-language-autonym="Kurdî" data-language-local-name="Kurdish" class="interlanguage-link-target"><span>Kurdî</span></a></li><li class="interlanguage-link interwiki-la mw-list-item"><a href="https://la.wikipedia.org/wiki/Potentia_Hydrogenii" title="Potentia Hydrogenii – Latin" lang="la" hreflang="la" data-title="Potentia Hydrogenii" data-language-autonym="Latina" data-language-local-name="Latin" class="interlanguage-link-target"><span>Latina</span></a></li><li class="interlanguage-link interwiki-lv mw-list-item"><a href="https://lv.wikipedia.org/wiki/PH" title="PH – Latvian" lang="lv" hreflang="lv" data-title="PH" data-language-autonym="Latviešu" data-language-local-name="Latvian" class="interlanguage-link-target"><span>Latviešu</span></a></li><li class="interlanguage-link interwiki-lb mw-list-item"><a href="https://lb.wikipedia.org/wiki/PH-W%C3%A4ert" title="PH-Wäert – Luxembourgish" lang="lb" hreflang="lb" data-title="PH-Wäert" data-language-autonym="Lëtzebuergesch" data-language-local-name="Luxembourgish" class="interlanguage-link-target"><span>Lëtzebuergesch</span></a></li><li class="interlanguage-link interwiki-lt mw-list-item"><a href="https://lt.wikipedia.org/wiki/Vandenilio_potencialas" title="Vandenilio potencialas – Lithuanian" lang="lt" hreflang="lt" data-title="Vandenilio potencialas" data-language-autonym="Lietuvių" data-language-local-name="Lithuanian" class="interlanguage-link-target"><span>Lietuvių</span></a></li><li class="interlanguage-link interwiki-lmo badge-Q17437796 badge-featuredarticle mw-list-item" title="featured article badge"><a href="https://lmo.wikipedia.org/wiki/PH" title="PH – Lombard" lang="lmo" hreflang="lmo" data-title="PH" data-language-autonym="Lombard" data-language-local-name="Lombard" class="interlanguage-link-target"><span>Lombard</span></a></li><li class="interlanguage-link interwiki-hu mw-list-item"><a href="https://hu.wikipedia.org/wiki/PH" title="PH – Hungarian" lang="hu" hreflang="hu" data-title="PH" data-language-autonym="Magyar" data-language-local-name="Hungarian" class="interlanguage-link-target"><span>Magyar</span></a></li><li class="interlanguage-link interwiki-mk mw-list-item"><a href="https://mk.wikipedia.org/wiki/%D0%92%D0%BE%D0%B4%D0%BE%D1%80%D0%BE%D0%B4%D0%B5%D0%BD_%D0%BF%D0%BE%D0%BA%D0%B0%D0%B7%D0%B0%D1%82%D0%B5%D0%BB" title="Водороден показател – Macedonian" lang="mk" hreflang="mk" data-title="Водороден показател" data-language-autonym="Македонски" data-language-local-name="Macedonian" class="interlanguage-link-target"><span>Македонски</span></a></li><li class="interlanguage-link interwiki-ml mw-list-item"><a href="https://ml.wikipedia.org/wiki/%E0%B4%AA%E0%B4%BF.%E0%B4%8E%E0%B4%9A%E0%B5%8D%E0%B4%9A%E0%B5%8D._%E0%B4%AE%E0%B5%82%E0%B4%B2%E0%B5%8D%E0%B4%AF%E0%B4%82" title="പി.എച്ച്. മൂല്യം – Malayalam" lang="ml" hreflang="ml" data-title="പി.എച്ച്. മൂല്യം" data-language-autonym="മലയാളം" data-language-local-name="Malayalam" class="interlanguage-link-target"><span>മലയാളം</span></a></li><li class="interlanguage-link interwiki-mr mw-list-item"><a href="https://mr.wikipedia.org/wiki/%E0%A4%AA%E0%A5%80.%E0%A4%8F%E0%A4%9A._%E0%A4%AE%E0%A5%82%E0%A4%B2%E0%A5%8D%E0%A4%AF" title="पी.एच. मूल्य – Marathi" lang="mr" hreflang="mr" data-title="पी.एच. मूल्य" data-language-autonym="मराठी" data-language-local-name="Marathi" class="interlanguage-link-target"><span>मराठी</span></a></li><li class="interlanguage-link interwiki-mnw mw-list-item"><a href="https://mnw.wikipedia.org/wiki/PH" title="PH – Mon" lang="mnw" hreflang="mnw" data-title="PH" data-language-autonym="ဘာသာမန်" data-language-local-name="Mon" class="interlanguage-link-target"><span>ဘာသာမန်</span></a></li><li class="interlanguage-link interwiki-ms mw-list-item"><a href="https://ms.wikipedia.org/wiki/PH" title="PH – Malay" lang="ms" hreflang="ms" data-title="PH" data-language-autonym="Bahasa Melayu" data-language-local-name="Malay" class="interlanguage-link-target"><span>Bahasa Melayu</span></a></li><li class="interlanguage-link interwiki-mn mw-list-item"><a href="https://mn.wikipedia.org/wiki/%D0%A0%D0%9D" title="РН – Mongolian" lang="mn" hreflang="mn" data-title="РН" data-language-autonym="Монгол" data-language-local-name="Mongolian" class="interlanguage-link-target"><span>Монгол</span></a></li><li class="interlanguage-link interwiki-my mw-list-item"><a href="https://my.wikipedia.org/wiki/PH" title="PH – Burmese" lang="my" hreflang="my" data-title="PH" data-language-autonym="မြန်မာဘာသာ" data-language-local-name="Burmese" class="interlanguage-link-target"><span>မြန်မာဘာသာ</span></a></li><li class="interlanguage-link interwiki-nl mw-list-item"><a href="https://nl.wikipedia.org/wiki/PH" title="PH – Dutch" lang="nl" hreflang="nl" data-title="PH" data-language-autonym="Nederlands" data-language-local-name="Dutch" class="interlanguage-link-target"><span>Nederlands</span></a></li><li class="interlanguage-link interwiki-ja mw-list-item"><a href="https://ja.wikipedia.org/wiki/%E6%B0%B4%E7%B4%A0%E3%82%A4%E3%82%AA%E3%83%B3%E6%8C%87%E6%95%B0" title="水素イオン指数 – Japanese" lang="ja" hreflang="ja" data-title="水素イオン指数" data-language-autonym="日本語" data-language-local-name="Japanese" class="interlanguage-link-target"><span>日本語</span></a></li><li class="interlanguage-link interwiki-frr mw-list-item"><a href="https://frr.wikipedia.org/wiki/PH_w%C3%A4%C3%A4rs" title="PH wäärs – Northern Frisian" lang="frr" hreflang="frr" data-title="PH wäärs" data-language-autonym="Nordfriisk" data-language-local-name="Northern Frisian" class="interlanguage-link-target"><span>Nordfriisk</span></a></li><li class="interlanguage-link interwiki-no mw-list-item"><a href="https://no.wikipedia.org/wiki/PH" title="PH – Norwegian Bokmål" lang="nb" hreflang="nb" data-title="PH" data-language-autonym="Norsk bokmål" data-language-local-name="Norwegian Bokmål" class="interlanguage-link-target"><span>Norsk bokmål</span></a></li><li class="interlanguage-link interwiki-nn mw-list-item"><a href="https://nn.wikipedia.org/wiki/PH" title="PH – Norwegian Nynorsk" lang="nn" hreflang="nn" data-title="PH" data-language-autonym="Norsk nynorsk" data-language-local-name="Norwegian Nynorsk" class="interlanguage-link-target"><span>Norsk nynorsk</span></a></li><li class="interlanguage-link interwiki-nov mw-list-item"><a href="https://nov.wikipedia.org/wiki/PH" title="PH – Novial" lang="nov" hreflang="nov" data-title="PH" data-language-autonym="Novial" data-language-local-name="Novial" class="interlanguage-link-target"><span>Novial</span></a></li><li class="interlanguage-link interwiki-oc mw-list-item"><a href="https://oc.wikipedia.org/wiki/PH" title="PH – Occitan" lang="oc" hreflang="oc" data-title="PH" data-language-autonym="Occitan" data-language-local-name="Occitan" class="interlanguage-link-target"><span>Occitan</span></a></li><li class="interlanguage-link interwiki-uz mw-list-item"><a href="https://uz.wikipedia.org/wiki/Vodorod_ko%CA%BBrsatkichi_(pH)" title="Vodorod koʻrsatkichi (pH) – Uzbek" lang="uz" hreflang="uz" data-title="Vodorod koʻrsatkichi (pH)" data-language-autonym="Oʻzbekcha / ўзбекча" data-language-local-name="Uzbek" class="interlanguage-link-target"><span>Oʻzbekcha / ўзбекча</span></a></li><li class="interlanguage-link interwiki-pa mw-list-item"><a href="https://pa.wikipedia.org/wiki/%E0%A8%AA%E0%A9%80.%E0%A8%90%E0%A9%B1%E0%A8%9A._(%E0%A8%B9%E0%A8%BE%E0%A8%88%E0%A8%A1%E0%A8%B0%E0%A9%8B%E0%A8%9C%E0%A8%A8_%E0%A8%B8%E0%A8%BC%E0%A8%95%E0%A8%A4%E0%A9%80)" title="ਪੀ.ਐੱਚ. (ਹਾਈਡਰੋਜਨ ਸ਼ਕਤੀ) – Punjabi" lang="pa" hreflang="pa" data-title="ਪੀ.ਐੱਚ. (ਹਾਈਡਰੋਜਨ ਸ਼ਕਤੀ)" data-language-autonym="ਪੰਜਾਬੀ" data-language-local-name="Punjabi" class="interlanguage-link-target"><span>ਪੰਜਾਬੀ</span></a></li><li class="interlanguage-link interwiki-pnb mw-list-item"><a href="https://pnb.wikipedia.org/wiki/%D9%BE%DB%8C_%D8%A7%DB%8C%DA%86" title="پی ایچ – Western Punjabi" lang="pnb" hreflang="pnb" data-title="پی ایچ" data-language-autonym="پنجابی" data-language-local-name="Western Punjabi" class="interlanguage-link-target"><span>پنجابی</span></a></li><li class="interlanguage-link interwiki-nds mw-list-item"><a href="https://nds.wikipedia.org/wiki/PH-Weert" title="PH-Weert – Low German" lang="nds" hreflang="nds" data-title="PH-Weert" data-language-autonym="Plattdüütsch" data-language-local-name="Low German" class="interlanguage-link-target"><span>Plattdüütsch</span></a></li><li class="interlanguage-link interwiki-pl mw-list-item"><a href="https://pl.wikipedia.org/wiki/Skala_pH" title="Skala pH – Polish" lang="pl" hreflang="pl" data-title="Skala pH" data-language-autonym="Polski" data-language-local-name="Polish" class="interlanguage-link-target"><span>Polski</span></a></li><li class="interlanguage-link interwiki-pt mw-list-item"><a href="https://pt.wikipedia.org/wiki/PH" title="PH – Portuguese" lang="pt" hreflang="pt" data-title="PH" data-language-autonym="Português" data-language-local-name="Portuguese" class="interlanguage-link-target"><span>Português</span></a></li><li class="interlanguage-link interwiki-ro mw-list-item"><a href="https://ro.wikipedia.org/wiki/PH" title="PH – Romanian" lang="ro" hreflang="ro" data-title="PH" data-language-autonym="Română" data-language-local-name="Romanian" class="interlanguage-link-target"><span>Română</span></a></li><li class="interlanguage-link interwiki-ru mw-list-item"><a href="https://ru.wikipedia.org/wiki/%D0%92%D0%BE%D0%B4%D0%BE%D1%80%D0%BE%D0%B4%D0%BD%D1%8B%D0%B9_%D0%BF%D0%BE%D0%BA%D0%B0%D0%B7%D0%B0%D1%82%D0%B5%D0%BB%D1%8C" title="Водородный показатель – Russian" lang="ru" hreflang="ru" data-title="Водородный показатель" data-language-autonym="Русский" data-language-local-name="Russian" class="interlanguage-link-target"><span>Русский</span></a></li><li class="interlanguage-link interwiki-sq mw-list-item"><a href="https://sq.wikipedia.org/wiki/PH" title="PH – Albanian" lang="sq" hreflang="sq" data-title="PH" data-language-autonym="Shqip" data-language-local-name="Albanian" class="interlanguage-link-target"><span>Shqip</span></a></li><li class="interlanguage-link interwiki-scn mw-list-item"><a href="https://scn.wikipedia.org/wiki/PH" title="PH – Sicilian" lang="scn" hreflang="scn" data-title="PH" data-language-autonym="Sicilianu" data-language-local-name="Sicilian" class="interlanguage-link-target"><span>Sicilianu</span></a></li><li class="interlanguage-link interwiki-simple mw-list-item"><a href="https://simple.wikipedia.org/wiki/PH" title="PH – Simple English" lang="en-simple" hreflang="en-simple" data-title="PH" data-language-autonym="Simple English" data-language-local-name="Simple English" class="interlanguage-link-target"><span>Simple English</span></a></li><li class="interlanguage-link interwiki-sk mw-list-item"><a href="https://sk.wikipedia.org/wiki/Kyslos%C5%A5" title="Kyslosť – Slovak" lang="sk" hreflang="sk" data-title="Kyslosť" data-language-autonym="Slovenčina" data-language-local-name="Slovak" class="interlanguage-link-target"><span>Slovenčina</span></a></li><li class="interlanguage-link interwiki-sl mw-list-item"><a href="https://sl.wikipedia.org/wiki/PH" title="PH – Slovenian" lang="sl" hreflang="sl" data-title="PH" data-language-autonym="Slovenščina" data-language-local-name="Slovenian" class="interlanguage-link-target"><span>Slovenščina</span></a></li><li class="interlanguage-link interwiki-so mw-list-item"><a href="https://so.wikipedia.org/wiki/PH" title="PH – Somali" lang="so" hreflang="so" data-title="PH" data-language-autonym="Soomaaliga" data-language-local-name="Somali" class="interlanguage-link-target"><span>Soomaaliga</span></a></li><li class="interlanguage-link interwiki-ckb mw-list-item"><a href="https://ckb.wikipedia.org/wiki/%D9%BE%DB%8C_%D8%A6%DB%8E%DA%86" title="پی ئێچ – Central Kurdish" lang="ckb" hreflang="ckb" data-title="پی ئێچ" data-language-autonym="کوردی" data-language-local-name="Central Kurdish" class="interlanguage-link-target"><span>کوردی</span></a></li><li class="interlanguage-link interwiki-sr mw-list-item"><a href="https://sr.wikipedia.org/wiki/PH_%D0%B2%D1%80%D0%B5%D0%B4%D0%BD%D0%BE%D1%81%D1%82" title="PH вредност – Serbian" lang="sr" hreflang="sr" data-title="PH вредност" data-language-autonym="Српски / srpski" data-language-local-name="Serbian" class="interlanguage-link-target"><span>Српски / srpski</span></a></li><li class="interlanguage-link interwiki-sh mw-list-item"><a href="https://sh.wikipedia.org/wiki/PH_vrednost" title="PH vrednost – Serbo-Croatian" lang="sh" hreflang="sh" data-title="PH vrednost" data-language-autonym="Srpskohrvatski / српскохрватски" data-language-local-name="Serbo-Croatian" class="interlanguage-link-target"><span>Srpskohrvatski / српскохрватски</span></a></li><li class="interlanguage-link interwiki-su mw-list-item"><a href="https://su.wikipedia.org/wiki/PH" title="PH – Sundanese" lang="su" hreflang="su" data-title="PH" data-language-autonym="Sunda" data-language-local-name="Sundanese" class="interlanguage-link-target"><span>Sunda</span></a></li><li class="interlanguage-link interwiki-fi mw-list-item"><a href="https://fi.wikipedia.org/wiki/Happamuus" title="Happamuus – Finnish" lang="fi" hreflang="fi" data-title="Happamuus" data-language-autonym="Suomi" data-language-local-name="Finnish" class="interlanguage-link-target"><span>Suomi</span></a></li><li class="interlanguage-link interwiki-sv mw-list-item"><a href="https://sv.wikipedia.org/wiki/PH" title="PH – Swedish" lang="sv" hreflang="sv" data-title="PH" data-language-autonym="Svenska" data-language-local-name="Swedish" class="interlanguage-link-target"><span>Svenska</span></a></li><li class="interlanguage-link interwiki-tl mw-list-item"><a href="https://tl.wikipedia.org/wiki/PH" title="PH – Tagalog" lang="tl" hreflang="tl" data-title="PH" data-language-autonym="Tagalog" data-language-local-name="Tagalog" class="interlanguage-link-target"><span>Tagalog</span></a></li><li class="interlanguage-link interwiki-ta mw-list-item"><a href="https://ta.wikipedia.org/wiki/%E0%AE%95%E0%AE%BE%E0%AE%B0%E0%AE%95%E0%AE%BE%E0%AE%9F%E0%AE%BF%E0%AE%A4%E0%AF%8D%E0%AE%A4%E0%AE%A9%E0%AF%8D%E0%AE%AE%E0%AF%88%E0%AE%9A%E0%AF%8D_%E0%AE%9A%E0%AF%81%E0%AE%9F%E0%AF%8D%E0%AE%9F%E0%AF%86%E0%AE%A3%E0%AF%8D" title="காரகாடித்தன்மைச் சுட்டெண் – Tamil" lang="ta" hreflang="ta" data-title="காரகாடித்தன்மைச் சுட்டெண்" data-language-autonym="தமிழ்" data-language-local-name="Tamil" class="interlanguage-link-target"><span>தமிழ்</span></a></li><li class="interlanguage-link interwiki-tt mw-list-item"><a href="https://tt.wikipedia.org/wiki/PH" title="PH – Tatar" lang="tt" hreflang="tt" data-title="PH" data-language-autonym="Татарча / tatarça" data-language-local-name="Tatar" class="interlanguage-link-target"><span>Татарча / tatarça</span></a></li><li class="interlanguage-link interwiki-te mw-list-item"><a href="https://te.wikipedia.org/wiki/PH" title="PH – Telugu" lang="te" hreflang="te" data-title="PH" data-language-autonym="తెలుగు" data-language-local-name="Telugu" class="interlanguage-link-target"><span>తెలుగు</span></a></li><li class="interlanguage-link interwiki-th mw-list-item"><a href="https://th.wikipedia.org/wiki/%E0%B8%9E%E0%B8%B5%E0%B9%80%E0%B8%AD%E0%B8%8A_(%E0%B9%80%E0%B8%84%E0%B8%A1%E0%B8%B5)" title="พีเอช (เคมี) – Thai" lang="th" hreflang="th" data-title="พีเอช (เคมี)" data-language-autonym="ไทย" data-language-local-name="Thai" class="interlanguage-link-target"><span>ไทย</span></a></li><li class="interlanguage-link interwiki-tr mw-list-item"><a href="https://tr.wikipedia.org/wiki/PH" title="PH – Turkish" lang="tr" hreflang="tr" data-title="PH" data-language-autonym="Türkçe" data-language-local-name="Turkish" class="interlanguage-link-target"><span>Türkçe</span></a></li><li class="interlanguage-link interwiki-uk mw-list-item"><a href="https://uk.wikipedia.org/wiki/PH" title="PH – Ukrainian" lang="uk" hreflang="uk" data-title="PH" data-language-autonym="Українська" data-language-local-name="Ukrainian" class="interlanguage-link-target"><span>Українська</span></a></li><li class="interlanguage-link interwiki-ur mw-list-item"><a href="https://ur.wikipedia.org/wiki/%D9%BE%DB%8C_%D8%A7%DB%8C%DA%86_(%DA%A9%DB%8C%D9%85%DB%8C%D8%A7%D8%A1)" title="پی ایچ (کیمیاء) – Urdu" lang="ur" hreflang="ur" data-title="پی ایچ (کیمیاء)" data-language-autonym="اردو" data-language-local-name="Urdu" class="interlanguage-link-target"><span>اردو</span></a></li><li class="interlanguage-link interwiki-vi mw-list-item"><a href="https://vi.wikipedia.org/wiki/PH" title="PH – Vietnamese" lang="vi" hreflang="vi" data-title="PH" data-language-autonym="Tiếng Việt" data-language-local-name="Vietnamese" class="interlanguage-link-target"><span>Tiếng Việt</span></a></li><li class="interlanguage-link interwiki-wa mw-list-item"><a href="https://wa.wikipedia.org/wiki/Potentiel_idrodjinne" title="Potentiel idrodjinne – Walloon" lang="wa" hreflang="wa" data-title="Potentiel idrodjinne" data-language-autonym="Walon" data-language-local-name="Walloon" class="interlanguage-link-target"><span>Walon</span></a></li><li class="interlanguage-link interwiki-zh-classical mw-list-item"><a href="https://zh-classical.wikipedia.org/wiki/%E9%85%B8%E9%B9%BC%E5%BA%A6" title="酸鹼度 – Literary Chinese" lang="lzh" hreflang="lzh" data-title="酸鹼度" data-language-autonym="文言" data-language-local-name="Literary Chinese" class="interlanguage-link-target"><span>文言</span></a></li><li class="interlanguage-link interwiki-vls mw-list-item"><a href="https://vls.wikipedia.org/wiki/PH" title="PH – West Flemish" lang="vls" hreflang="vls" data-title="PH" data-language-autonym="West-Vlams" data-language-local-name="West Flemish" class="interlanguage-link-target"><span>West-Vlams</span></a></li><li class="interlanguage-link interwiki-war mw-list-item"><a href="https://war.wikipedia.org/wiki/PH" title="PH – Waray" lang="war" hreflang="war" data-title="PH" data-language-autonym="Winaray" data-language-local-name="Waray" class="interlanguage-link-target"><span>Winaray</span></a></li><li class="interlanguage-link interwiki-wuu mw-list-item"><a href="https://wuu.wikipedia.org/wiki/PH%E5%80%BC" title="PH值 – Wu" lang="wuu" hreflang="wuu" data-title="PH值" data-language-autonym="吴语" data-language-local-name="Wu" class="interlanguage-link-target"><span>吴语</span></a></li><li class="interlanguage-link interwiki-zh-yue mw-list-item"><a href="https://zh-yue.wikipedia.org/wiki/%E9%85%B8%E9%B9%BC%E5%BA%A6" title="酸鹼度 – Cantonese" lang="yue" hreflang="yue" data-title="酸鹼度" data-language-autonym="粵語" data-language-local-name="Cantonese" class="interlanguage-link-target"><span>粵語</span></a></li><li class="interlanguage-link interwiki-zh mw-list-item"><a href="https://zh.wikipedia.org/wiki/PH%E5%80%BC" title="PH值 – Chinese" lang="zh" hreflang="zh" data-title="PH值" data-language-autonym="中文" data-language-local-name="Chinese" class="interlanguage-link-target"><span>中文</span></a></li> </ul> <div class="after-portlet after-portlet-lang"><span class="wb-langlinks-edit wb-langlinks-link"><a href="https://www.wikidata.org/wiki/Special:EntityPage/Q40936#sitelinks-wikipedia" title="Edit interlanguage links" class="wbc-editpage">Edit links</a></span></div> </div> </div> </div> </header> <div class="vector-page-toolbar"> <div class="vector-page-toolbar-container"> <div id="left-navigation"> <nav aria-label="Namespaces"> <div id="p-associated-pages" class="vector-menu vector-menu-tabs mw-portlet mw-portlet-associated-pages" > <div 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i{font-style:normal}.mw-parser-output .hatnote+link+.hatnote{margin-top:-0.5em}@media print{body.ns-0 .mw-parser-output .hatnote{display:none!important}}</style><div role="note" class="hatnote navigation-not-searchable">For other uses, see <a href="/wiki/PH_(disambiguation)" class="mw-disambig" title="PH (disambiguation)">PH (disambiguation)</a>.</div> <p class="mw-empty-elt"> </p> <figure class="mw-default-size mw-halign-right" typeof="mw:File/Thumb"><a href="/wiki/File:PH_scale_3.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/b/bd/PH_scale_3.jpg/220px-PH_scale_3.jpg" decoding="async" width="220" height="165" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/b/bd/PH_scale_3.jpg/330px-PH_scale_3.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/b/bd/PH_scale_3.jpg/440px-PH_scale_3.jpg 2x" data-file-width="4032" data-file-height="3024" /></a><figcaption>Test tubes containing solutions of pH 1–10 colored with <a href="/wiki/Universal_indicator" title="Universal indicator">an indicator</a></figcaption></figure> <style data-mw-deduplicate="TemplateStyles:r1129693374">.mw-parser-output .hlist dl,.mw-parser-output .hlist ol,.mw-parser-output .hlist ul{margin:0;padding:0}.mw-parser-output .hlist dd,.mw-parser-output .hlist dt,.mw-parser-output .hlist li{margin:0;display:inline}.mw-parser-output .hlist.inline,.mw-parser-output .hlist.inline dl,.mw-parser-output .hlist.inline ol,.mw-parser-output .hlist.inline ul,.mw-parser-output .hlist dl dl,.mw-parser-output .hlist dl ol,.mw-parser-output .hlist dl ul,.mw-parser-output .hlist ol dl,.mw-parser-output .hlist ol ol,.mw-parser-output .hlist ol ul,.mw-parser-output .hlist ul dl,.mw-parser-output .hlist ul ol,.mw-parser-output .hlist ul ul{display:inline}.mw-parser-output .hlist .mw-empty-li{display:none}.mw-parser-output .hlist dt::after{content:": "}.mw-parser-output .hlist dd::after,.mw-parser-output .hlist li::after{content:" · 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dd:last-child::after,.mw-parser-output .hlist li dt:last-child::after,.mw-parser-output .hlist li li:last-child::after{content:")";font-weight:normal}.mw-parser-output .hlist ol{counter-reset:listitem}.mw-parser-output .hlist ol>li{counter-increment:listitem}.mw-parser-output .hlist ol>li::before{content:" "counter(listitem)"\a0 "}.mw-parser-output .hlist dd ol>li:first-child::before,.mw-parser-output .hlist dt ol>li:first-child::before,.mw-parser-output .hlist li ol>li:first-child::before{content:" ("counter(listitem)"\a0 "}</style><style data-mw-deduplicate="TemplateStyles:r1246091330">.mw-parser-output .sidebar{width:22em;float:right;clear:right;margin:0.5em 0 1em 1em;background:var(--background-color-neutral-subtle,#f8f9fa);border:1px solid var(--border-color-base,#a2a9b1);padding:0.2em;text-align:center;line-height:1.4em;font-size:88%;border-collapse:collapse;display:table}body.skin-minerva .mw-parser-output .sidebar{display:table!important;float:right!important;margin:0.5em 0 1em 1em!important}.mw-parser-output .sidebar-subgroup{width:100%;margin:0;border-spacing:0}.mw-parser-output .sidebar-left{float:left;clear:left;margin:0.5em 1em 1em 0}.mw-parser-output .sidebar-none{float:none;clear:both;margin:0.5em 1em 1em 0}.mw-parser-output .sidebar-outer-title{padding:0 0.4em 0.2em;font-size:125%;line-height:1.2em;font-weight:bold}.mw-parser-output .sidebar-top-image{padding:0.4em}.mw-parser-output .sidebar-top-caption,.mw-parser-output .sidebar-pretitle-with-top-image,.mw-parser-output .sidebar-caption{padding:0.2em 0.4em 0;line-height:1.2em}.mw-parser-output .sidebar-pretitle{padding:0.4em 0.4em 0;line-height:1.2em}.mw-parser-output .sidebar-title,.mw-parser-output .sidebar-title-with-pretitle{padding:0.2em 0.8em;font-size:145%;line-height:1.2em}.mw-parser-output .sidebar-title-with-pretitle{padding:0.1em 0.4em}.mw-parser-output .sidebar-image{padding:0.2em 0.4em 0.4em}.mw-parser-output .sidebar-heading{padding:0.1em 0.4em}.mw-parser-output .sidebar-content{padding:0 0.5em 0.4em}.mw-parser-output .sidebar-content-with-subgroup{padding:0.1em 0.4em 0.2em}.mw-parser-output .sidebar-above,.mw-parser-output .sidebar-below{padding:0.3em 0.8em;font-weight:bold}.mw-parser-output .sidebar-collapse .sidebar-above,.mw-parser-output .sidebar-collapse .sidebar-below{border-top:1px solid #aaa;border-bottom:1px solid #aaa}.mw-parser-output .sidebar-navbar{text-align:right;font-size:115%;padding:0 0.4em 0.4em}.mw-parser-output .sidebar-list-title{padding:0 0.4em;text-align:left;font-weight:bold;line-height:1.6em;font-size:105%}.mw-parser-output .sidebar-list-title-c{padding:0 0.4em;text-align:center;margin:0 3.3em}@media(max-width:640px){body.mediawiki .mw-parser-output .sidebar{width:100%!important;clear:both;float:none!important;margin-left:0!important;margin-right:0!important}}body.skin--responsive .mw-parser-output .sidebar a>img{max-width:none!important}@media screen{html.skin-theme-clientpref-night .mw-parser-output .sidebar:not(.notheme) .sidebar-list-title,html.skin-theme-clientpref-night .mw-parser-output .sidebar:not(.notheme) .sidebar-title-with-pretitle{background:transparent!important}html.skin-theme-clientpref-night .mw-parser-output .sidebar:not(.notheme) .sidebar-title-with-pretitle a{color:var(--color-progressive)!important}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .sidebar:not(.notheme) .sidebar-list-title,html.skin-theme-clientpref-os .mw-parser-output .sidebar:not(.notheme) .sidebar-title-with-pretitle{background:transparent!important}html.skin-theme-clientpref-os .mw-parser-output .sidebar:not(.notheme) .sidebar-title-with-pretitle a{color:var(--color-progressive)!important}}@media print{body.ns-0 .mw-parser-output .sidebar{display:none!important}}</style><table class="sidebar nomobile nowraplinks"><tbody><tr><th class="sidebar-title" style="background:#d3d3d3;">Acids and bases</th></tr><tr><td class="sidebar-image"><span typeof="mw:File"><a href="/wiki/File:Acetic-acid-dissociation-3D-balls.png" class="mw-file-description" title="Diagrammatic representation of the dissociation of acetic acid in aqueous solution to acetate and hydronium ions."><img alt="Diagrammatic representation of the dissociation of acetic acid in aqueous solution to acetate and hydronium ions." src="//upload.wikimedia.org/wikipedia/commons/thumb/9/96/Acetic-acid-dissociation-3D-balls.png/220px-Acetic-acid-dissociation-3D-balls.png" decoding="async" width="220" height="52" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/9/96/Acetic-acid-dissociation-3D-balls.png/330px-Acetic-acid-dissociation-3D-balls.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/9/96/Acetic-acid-dissociation-3D-balls.png/440px-Acetic-acid-dissociation-3D-balls.png 2x" data-file-width="2150" data-file-height="513" /></a></span></td></tr><tr><td class="sidebar-content hlist" style="padding:0.2em 0 0.75em;"> <ul><li><a href="/wiki/Acceptor_number" class="mw-redirect" title="Acceptor number">Acceptor number</a></li> <li><a href="/wiki/Acid" title="Acid">Acid</a></li> <li><a href="/wiki/Acid%E2%80%93base_reaction" title="Acid–base reaction">Acid–base reaction</a></li> <li><a href="/wiki/Acid%E2%80%93base_homeostasis" title="Acid–base homeostasis">Acid–base homeostasis</a></li> <li><a href="/wiki/Acid_strength" title="Acid strength">Acid strength</a></li> <li><a href="/wiki/Acidity_function" title="Acidity function">Acidity function</a></li> <li><a href="/wiki/Amphoterism" title="Amphoterism">Amphoterism</a></li> <li><a href="/wiki/Base_(chemistry)" title="Base (chemistry)">Base</a></li> <li><a href="/wiki/Buffer_solution" title="Buffer solution">Buffer solutions</a></li> <li><a href="/wiki/Dissociation_constant" title="Dissociation constant">Dissociation constant</a></li> <li><a href="/wiki/Donor_number" title="Donor number">Donor number</a></li> <li><a href="/wiki/Equilibrium_chemistry" title="Equilibrium chemistry">Equilibrium chemistry</a></li> <li><a href="/wiki/Acid%E2%80%93base_extraction" title="Acid–base extraction">Extraction</a></li> <li><a href="/wiki/Hammett_acidity_function" title="Hammett acidity function">Hammett acidity function</a></li> <li><a class="mw-selflink selflink">pH</a></li> <li><a href="/wiki/Proton_affinity" title="Proton affinity">Proton affinity</a></li> <li><a href="/wiki/Self-ionization_of_water" title="Self-ionization of water">Self-ionization of water</a></li> <li><a href="/wiki/Acid%E2%80%93base_titration" title="Acid–base titration">Titration</a></li> <li><a href="/wiki/Lewis_acid_catalysis" title="Lewis acid catalysis">Lewis acid catalysis</a></li> <li><a href="/wiki/Frustrated_Lewis_pair" title="Frustrated Lewis pair">Frustrated Lewis pair</a></li> <li><a href="/wiki/Chiral_Lewis_acid" title="Chiral Lewis acid">Chiral Lewis acid</a></li> <li><a href="/wiki/ECW_model" title="ECW model">ECW model</a></li></ul></td> </tr><tr><th class="sidebar-heading" style="background:#e5e5e5;"> <a href="/wiki/Acid" title="Acid">Acid</a> types</th></tr><tr><td class="sidebar-content hlist" style="padding:0.2em 0 0.75em;"> <ul><li><a href="/wiki/Br%C3%B8nsted%E2%80%93Lowry_acid%E2%80%93base_theory" title="Brønsted–Lowry acid–base theory">Brønsted–Lowry</a></li> <li><a href="/wiki/Lewis_acids_and_bases" title="Lewis acids and bases">Lewis</a></li> <li><a href="/wiki/Mineral_acid" title="Mineral acid">Mineral</a></li> <li><a href="/wiki/Organic_acid" title="Organic acid">Organic</a></li> <li><a href="/wiki/Acidic_oxide" title="Acidic oxide">Oxide</a></li> <li><a href="/wiki/Strong_acid" class="mw-redirect" title="Strong acid">Strong</a></li> <li><a href="/wiki/Superacid" title="Superacid">Superacids</a></li> <li><a href="/wiki/Weak_acid" class="mw-redirect" title="Weak acid">Weak</a></li> <li><a href="/wiki/Solid_acid" title="Solid acid">Solid</a></li></ul></td> </tr><tr><th class="sidebar-heading" style="background:#e5e5e5;"> <a href="/wiki/Base_(chemistry)" title="Base (chemistry)">Base</a> types</th></tr><tr><td class="sidebar-content hlist" style="padding:0.2em 0 0.75em;"> <ul><li><a href="/wiki/Br%C3%B8nsted%E2%80%93Lowry_acid%E2%80%93base_theory" title="Brønsted–Lowry acid–base theory">Brønsted–Lowry</a></li> <li><a href="/wiki/Lewis_acids_and_bases" title="Lewis acids and bases">Lewis</a></li> <li><a href="/wiki/Organic_base" title="Organic base">Organic</a></li> <li><a href="/wiki/Basic_oxide" title="Basic oxide">Oxide</a></li> <li><a href="/wiki/Base_(chemistry)#Strong_bases" title="Base (chemistry)">Strong</a></li> <li><a href="/wiki/Superbase" title="Superbase">Superbases</a></li> <li><a href="/wiki/Non-nucleophilic_base" title="Non-nucleophilic base">Non-nucleophilic</a></li> <li><a href="/wiki/Weak_base" title="Weak base">Weak</a></li></ul></td> </tr><tr><td class="sidebar-navbar"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374"><style data-mw-deduplicate="TemplateStyles:r1239400231">.mw-parser-output .navbar{display:inline;font-size:88%;font-weight:normal}.mw-parser-output .navbar-collapse{float:left;text-align:left}.mw-parser-output .navbar-boxtext{word-spacing:0}.mw-parser-output .navbar ul{display:inline-block;white-space:nowrap;line-height:inherit}.mw-parser-output .navbar-brackets::before{margin-right:-0.125em;content:"[ "}.mw-parser-output .navbar-brackets::after{margin-left:-0.125em;content:" ]"}.mw-parser-output .navbar li{word-spacing:-0.125em}.mw-parser-output .navbar a>span,.mw-parser-output .navbar a>abbr{text-decoration:inherit}.mw-parser-output .navbar-mini abbr{font-variant:small-caps;border-bottom:none;text-decoration:none;cursor:inherit}.mw-parser-output .navbar-ct-full{font-size:114%;margin:0 7em}.mw-parser-output .navbar-ct-mini{font-size:114%;margin:0 4em}html.skin-theme-clientpref-night .mw-parser-output .navbar li a abbr{color:var(--color-base)!important}@media(prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .navbar li a abbr{color:var(--color-base)!important}}@media print{.mw-parser-output .navbar{display:none!important}}</style><div class="navbar plainlinks hlist navbar-mini"><ul><li class="nv-view"><a href="/wiki/Template:Acids_and_bases" title="Template:Acids and bases"><abbr title="View this template">v</abbr></a></li><li class="nv-talk"><a href="/wiki/Template_talk:Acids_and_bases" title="Template talk:Acids and bases"><abbr title="Discuss this template">t</abbr></a></li><li class="nv-edit"><a href="/wiki/Special:EditPage/Template:Acids_and_bases" title="Special:EditPage/Template:Acids and bases"><abbr title="Edit this template">e</abbr></a></li></ul></div></td></tr></tbody></table><p>In <a href="/wiki/Chemistry" title="Chemistry">chemistry</a>, <b>pH</b> (<span class="rt-commentedText nowrap"><span class="IPA nopopups noexcerpt" lang="en-fonipa"><a href="/wiki/Help:IPA/English" title="Help:IPA/English">/<span style="border-bottom:1px dotted"><span title="'p' in 'pie'">p</span><span title="/iː/: 'ee' in 'fleece'">iː</span><span title="/ˈ/: primary stress follows">ˈ</span><span title="/eɪ/: 'a' in 'face'">eɪ</span><span title="/tʃ/: 'ch' in 'China'">tʃ</span></span>/</a></span></span> <a href="/wiki/Help:Pronunciation_respelling_key" title="Help:Pronunciation respelling key"><i title="English pronunciation respelling">pee-<span style="font-size:90%">AYCH</span></i></a>), also referred to as <i>acidity</i> or <i>basicity</i>, historically denotes "<a href="/wiki/Chemical_potential" title="Chemical potential">potential</a> of <a href="/wiki/Hydrogen" title="Hydrogen">hydrogen</a>" (or "power of hydrogen").<sup id="cite_ref-1" class="reference"><a href="#cite_note-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> It is a <a href="/wiki/Logarithmic_scale" title="Logarithmic scale">logarithmic scale</a> used to specify the <a href="/wiki/Acid" title="Acid">acidity</a> or <a href="/wiki/Base_(chemistry)" title="Base (chemistry)">basicity</a> of <a href="/wiki/Aqueous_solution" title="Aqueous solution">aqueous solutions</a>. Acidic solutions (solutions with higher concentrations of hydrogen (<a href="/wiki/Hydrogen_ion#Cation_(positively_charged)" title="Hydrogen ion"><style data-mw-deduplicate="TemplateStyles:r1123817410">'"`UNIQ--templatestyles-0000000C-QINU`"'</style><span class="chemf nowrap">H<sup class="template-chem2-sup">+</sup></span></a>) <a href="/wiki/Ion" title="Ion">ions</a>) are measured to have lower pH values than basic or <a href="/wiki/Alkali" title="Alkali">alkaline</a> solutions. </p><p>The pH scale is logarithmic and inversely indicates the <a href="/wiki/Thermodynamic_activity" title="Thermodynamic activity">activity</a> of <a href="/wiki/Hydronium" title="Hydronium">hydrogen ions</a> in the solution </p> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle {\ce {pH}}=-\log _{10}(a_{{\ce {H+}}})\thickapprox -\log _{10}([{\ce {H+}}])}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mrow class="MJX-TeXAtom-ORD"> <mtext>pH</mtext> </mrow> <mo>=</mo> <mo>−</mo> <msub> <mi>log</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>10</mn> </mrow> </msub> <mo>⁡</mo> <mo stretchy="false">(</mo> <msub> <mi>a</mi> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-ORD"> <msup> <mtext>H</mtext> <mrow class="MJX-TeXAtom-ORD"> <mo>+</mo> </mrow> </msup> </mrow> </mrow> </msub> <mo stretchy="false">)</mo> <mo class="MJX-variant">≈</mo> <mo>−</mo> <msub> <mi>log</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>10</mn> </mrow> </msub> <mo>⁡</mo> <mo stretchy="false">(</mo> <mo stretchy="false">[</mo> <mrow class="MJX-TeXAtom-ORD"> <msup> <mtext>H</mtext> <mrow class="MJX-TeXAtom-ORD"> <mo>+</mo> </mrow> </msup> </mrow> <mo stretchy="false">]</mo> <mo stretchy="false">)</mo> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle {\ce {pH}}=-\log _{10}(a_{{\ce {H+}}})\thickapprox -\log _{10}([{\ce {H+}}])}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/a1d35385abf8498456c8f4db35c55b00629d7b7b" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:35.382ex; height:3.009ex;" alt="{\displaystyle {\ce {pH}}=-\log _{10}(a_{{\ce {H+}}})\thickapprox -\log _{10}([{\ce {H+}}])}"></span></dd></dl> <p>where [H<sup>+</sup>] is the <a href="/wiki/Equilibrium_chemistry" title="Equilibrium chemistry">equilibrium</a> <a href="/wiki/Molar_concentration" title="Molar concentration">molar concentration</a> of H<sup>+</sup> (in M = mol/L) in the solution. At 25 <a href="/wiki/Celsius" title="Celsius">°C</a> (77 <a href="/wiki/Fahrenheit" title="Fahrenheit">°F</a>), solutions of which the pH is less than 7 are acidic, and solutions of which the pH is greater than 7 are basic. Solutions with a pH of 7 at 25 °C are neutral (i.e. have the same concentration of H<sup>+</sup> ions as OH<sup>−</sup> ions, i.e. the same as <a href="/wiki/Pure_water" class="mw-redirect" title="Pure water">pure water</a>). The neutral value of the pH depends on the temperature and is lower than 7 if the temperature increases above 25 °C. The pH range is commonly given as zero to 14, but a pH value can be less than 0 for very concentrated <a href="/wiki/Acid_strength" title="Acid strength">strong acids</a> or greater than 14 for very concentrated <a href="/wiki/Base_(chemistry)#Strong_bases" title="Base (chemistry)">strong bases</a>.<sup id="cite_ref-2" class="reference"><a href="#cite_note-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup> </p><p>The pH scale is <a href="/wiki/Measurement_traceability" class="mw-redirect" title="Measurement traceability">traceable</a> to a set of standard solutions whose pH is established by international agreement.<sup id="cite_ref-covington3_3-0" class="reference"><a href="#cite_note-covington3-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> Primary pH standard values are determined using a <a href="/wiki/Galvanic_cell" title="Galvanic cell">concentration cell with transference</a> by measuring the potential difference between a <a href="/wiki/Hydrogen_electrode" class="mw-redirect" title="Hydrogen electrode">hydrogen electrode</a> and a <a href="/wiki/Standard_electrode_potential_(data_page)" title="Standard electrode potential (data page)">standard electrode</a> such as the <a href="/wiki/Silver_chloride_electrode" title="Silver chloride electrode">silver chloride electrode</a>. The pH of aqueous solutions can be measured with a <a href="/wiki/Glass_electrode" title="Glass electrode">glass electrode</a> and a <a href="/wiki/PH_meter" title="PH meter">pH meter</a> or a color-changing <a href="/wiki/PH_indicator" title="PH indicator">indicator</a>. Measurements of pH are important in <a href="/wiki/Chemistry" title="Chemistry">chemistry</a>, <a href="/wiki/Agronomy" title="Agronomy">agronomy</a>, medicine, water treatment, and many other applications. </p> <meta property="mw:PageProp/toc" /> <div class="mw-heading mw-heading2"><h2 id="History">History</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=PH&action=edit&section=1" title="Edit section: History"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div><p> In 1909, the <a href="/wiki/Danish_people" class="mw-redirect" title="Danish people">Danish</a> chemist <a href="/wiki/S._P._L._S%C3%B8rensen" title="S. P. L. Sørensen">Søren Peter Lauritz Sørensen</a> introduced the concept of pH at the <a href="/wiki/Carlsberg_Laboratory" title="Carlsberg Laboratory">Carlsberg Laboratory</a>,<sup id="cite_ref-Sørensen2_4-0" class="reference"><a href="#cite_note-Sørensen2-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup> originally using the notation "p<sub>H•</sub>", with H• as a subscript to the lowercase p. The concept was later revised in 1924 to the modern pH to accommodate definitions and measurements in terms of electrochemical cells.</p><blockquote><p>For the sign <i>p</i>, I propose the name 'hydrogen ion exponent' and the symbol p<sub>H•</sub>. Then, for the hydrogen ion exponent (p<sub>H•</sub>) of a solution, the negative value of the <a href="/wiki/Common_logarithm" title="Common logarithm">Briggsian logarithm</a> of the related hydrogen ion <a href="/wiki/Equivalent_concentration" title="Equivalent concentration">normality factor</a> is to be understood.<sup id="cite_ref-Sørensen2_4-1" class="reference"><a href="#cite_note-Sørensen2-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup></p></blockquote><p>Sørensen did not explain why he used the letter p, and the exact meaning of the letter is still disputed.<sup id="cite_ref-5" class="reference"><a href="#cite_note-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-6" class="reference"><a href="#cite_note-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup> Sørensen described a way of measuring pH using <i>potential</i> differences, and it represents the negative <i>power</i> of 10 in the concentration of hydrogen ions. The letter <i>p</i> could stand for the French <i>puissance,</i> German <i>Potenz,</i> or Danish <i>potens</i>, all meaning "power", or it could mean "potential". All of these words start with the letter <i>p</i> in <a href="/wiki/French_language" title="French language">French</a>, <a href="/wiki/German_language" title="German language">German</a>, and <a href="/wiki/Danish_language" title="Danish language">Danish</a>, which were the languages in which Sørensen published: Carlsberg Laboratory was French-speaking; German was the dominant language of scientific publishing; Sørensen was Danish. He also used the letter <i>q</i> in much the same way elsewhere in the paper, and he might have arbitrarily labelled the test solution "p" and the reference solution "q"; these letters are often paired with e4 then e5.<sup id="cite_ref-7" class="reference"><a href="#cite_note-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup> Some literature sources suggest that "pH" stands for the <a href="/wiki/Latin_language" class="mw-redirect" title="Latin language">Latin term</a> <i>pondus hydrogenii</i> (quantity of hydrogen) or <i>potentia hydrogenii</i> (power of hydrogen), although this is not supported by Sørensen's writings.<sup id="cite_ref-Otterson2_8-0" class="reference"><a href="#cite_note-Otterson2-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Lian2_9-0" class="reference"><a href="#cite_note-Lian2-9"><span class="cite-bracket">[</span>9<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Bradley2_10-0" class="reference"><a href="#cite_note-Bradley2-10"><span class="cite-bracket">[</span>10<span class="cite-bracket">]</span></a></sup> </p><p>In modern <a href="/wiki/Chemistry" title="Chemistry">chemistry</a>, the p stands for "the negative <a href="/wiki/Common_logarithm" title="Common logarithm">decimal logarithm</a> of", and is used in the term p<i>K</i><sub>a</sub> for <a href="/wiki/Acid_dissociation_constant" title="Acid dissociation constant">acid dissociation constants</a>,<sup id="cite_ref-Jens2_11-0" class="reference"><a href="#cite_note-Jens2-11"><span class="cite-bracket">[</span>11<span class="cite-bracket">]</span></a></sup> so pH is "the negative <a href="/wiki/Common_logarithm" title="Common logarithm">decimal logarithm of</a> H<sup>+</sup> ion concentration", while pOH is "the negative decimal logarithm of OH<sup>−</sup> ion concentration". </p><p> Bacteriologist <a href="/wiki/Alice_Catherine_Evans" title="Alice Catherine Evans">Alice Catherine Evans</a>, who influenced <a href="/wiki/Dairy" title="Dairy">dairying</a> and <a href="/wiki/Food_safety" title="Food safety">food safety</a>, credited <a href="/wiki/William_Mansfield_Clark" title="William Mansfield Clark">William Mansfield Clark</a> and colleagues, including herself, with developing pH measuring methods in the 1910s, which had a wide influence on laboratory and industrial use thereafter. In her memoir, she does not mention how much, or how little, Clark and colleagues knew about Sørensen's work a few years prior.<sup id="cite_ref-Evans-Memoirs2_12-0" class="reference"><a href="#cite_note-Evans-Memoirs2-12"><span class="cite-bracket">[</span>12<span class="cite-bracket">]</span></a></sup> She said:</p><blockquote><p>In these studies [of bacterial metabolism] Dr. Clark's attention was directed to the effect of acid on the growth of bacteria. He found that it is the intensity of the acid in terms of hydrogen-ion concentration that affects their growth. But existing methods of measuring acidity determined the quantity, not the intensity, of the acid. Next, with his collaborators, Dr. Clark developed accurate methods for measuring hydrogen-ion concentration. These methods replaced the inaccurate titration method of determining the acid content in use in biologic laboratories throughout the world. Also they were found to be applicable in many industrial and other processes in which they came into wide usage.<sup id="cite_ref-Evans-Memoirs2_12-1" class="reference"><a href="#cite_note-Evans-Memoirs2-12"><span class="cite-bracket">[</span>12<span class="cite-bracket">]</span></a></sup></p></blockquote><p>The first <a href="/wiki/Electronics" title="Electronics">electronic</a> method for measuring pH was invented by <a href="/wiki/Arnold_Orville_Beckman" class="mw-redirect" title="Arnold Orville Beckman">Arnold Orville Beckman</a>, a professor at the <a href="/wiki/California_Institute_of_Technology" title="California Institute of Technology">California Institute of Technology</a> in 1934.<sup id="cite_ref-13" class="reference"><a href="#cite_note-13"><span class="cite-bracket">[</span>13<span class="cite-bracket">]</span></a></sup> It was in response to a request from the local citrus grower <a href="/wiki/Sunkist_Growers,_Incorporated" title="Sunkist Growers, Incorporated">Sunkist</a>, which wanted a better method for quickly testing the pH of lemons they were picking from their nearby orchards.<sup id="cite_ref-14" class="reference"><a href="#cite_note-14"><span class="cite-bracket">[</span>14<span class="cite-bracket">]</span></a></sup> </p><div class="mw-heading mw-heading2"><h2 id="Definition">Definition</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=PH&action=edit&section=2" title="Edit section: Definition"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <div class="mw-heading mw-heading3"><h3 id="pH">pH</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=PH&action=edit&section=3" title="Edit section: pH"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The pH of a solution is defined as the decimal <a href="/wiki/Logarithm" title="Logarithm">logarithm</a> of the reciprocal of the <a href="/wiki/Hydrogen_ion" title="Hydrogen ion">hydrogen ion</a> <a href="/wiki/Activity_(chemistry)" class="mw-redirect" title="Activity (chemistry)">activity</a>, <i>a</i><sub>H</sub>+.<sup id="cite_ref-covington3_3-1" class="reference"><a href="#cite_note-covington3-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> Mathematically, pH is expressed as: </p> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle {\ce {pH}}=-\log _{10}(a_{{\ce {H+}}})=\log _{10}\left({\frac {1}{a_{{\ce {H+}}}}}\right)}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mrow class="MJX-TeXAtom-ORD"> <mtext>pH</mtext> </mrow> <mo>=</mo> <mo>−</mo> <msub> <mi>log</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>10</mn> </mrow> </msub> <mo>⁡</mo> <mo stretchy="false">(</mo> <msub> <mi>a</mi> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-ORD"> <msup> <mtext>H</mtext> <mrow class="MJX-TeXAtom-ORD"> <mo>+</mo> </mrow> </msup> </mrow> </mrow> </msub> <mo stretchy="false">)</mo> <mo>=</mo> <msub> <mi>log</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>10</mn> </mrow> </msub> <mo>⁡</mo> <mrow> <mo>(</mo> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <mn>1</mn> <msub> <mi>a</mi> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-ORD"> <msup> <mtext>H</mtext> <mrow class="MJX-TeXAtom-ORD"> <mo>+</mo> </mrow> </msup> </mrow> </mrow> </msub> </mfrac> </mrow> <mo>)</mo> </mrow> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle {\ce {pH}}=-\log _{10}(a_{{\ce {H+}}})=\log _{10}\left({\frac {1}{a_{{\ce {H+}}}}}\right)}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/932bace628e5b8db56e6220cc82210336491b3ab" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -2.505ex; width:34.984ex; height:6.176ex;" alt="{\displaystyle {\ce {pH}}=-\log _{10}(a_{{\ce {H+}}})=\log _{10}\left({\frac {1}{a_{{\ce {H+}}}}}\right)}"></span></dd></dl> <p>For example, for a solution with a hydrogen ion activity of <span class="nowrap"><span data-sort-value="6997499999999999999♠"></span>5<span style="margin-left:0.25em;margin-right:0.15em;">×</span>10<sup>−6</sup> <a href="/wiki/Mole_(unit)" title="Mole (unit)">mol</a>/<a href="/wiki/Litre" title="Litre">L</a></span> (i.e., the concentration of hydrogen ions), the pH of the solution can be calculated as follows: </p> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle {\ce {pH}}=-\log _{10}(5\times 10^{-6})=5.3}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mrow class="MJX-TeXAtom-ORD"> <mtext>pH</mtext> </mrow> <mo>=</mo> <mo>−</mo> <msub> <mi>log</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>10</mn> </mrow> </msub> <mo>⁡</mo> <mo stretchy="false">(</mo> <mn>5</mn> <mo>×</mo> <msup> <mn>10</mn> <mrow class="MJX-TeXAtom-ORD"> <mo>−</mo> <mn>6</mn> </mrow> </msup> <mo stretchy="false">)</mo> <mo>=</mo> <mn>5.3</mn> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle {\ce {pH}}=-\log _{10}(5\times 10^{-6})=5.3}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/1cf76a8ab825684516143408b22f4c3f8435fa8d" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:29.717ex; height:3.176ex;" alt="{\displaystyle {\ce {pH}}=-\log _{10}(5\times 10^{-6})=5.3}"></span></dd></dl> <p>The concept of pH was developed because <a href="/wiki/Ion-selective_electrodes" class="mw-redirect" title="Ion-selective electrodes">ion-selective electrodes</a>, which are used to measure pH, respond to activity. The electrode potential, <i>E</i>, follows the <a href="/wiki/Nernst_equation" title="Nernst equation">Nernst equation</a> for the hydrogen ion, which can be expressed as: </p> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle E=E^{0}+{\frac {RT}{F}}\ln(a_{{\ce {H+}}})=E^{0}-{\frac {RT\ \ln {10}}{F}}{\ce {pH}}\approx E^{0}-{\frac {2.303\ RT}{F}}{\ce {pH}}}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mi>E</mi> <mo>=</mo> <msup> <mi>E</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>0</mn> </mrow> </msup> <mo>+</mo> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <mrow> <mi>R</mi> <mi>T</mi> </mrow> <mi>F</mi> </mfrac> </mrow> <mi>ln</mi> <mo>⁡</mo> <mo stretchy="false">(</mo> <msub> <mi>a</mi> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-ORD"> <msup> <mtext>H</mtext> <mrow class="MJX-TeXAtom-ORD"> <mo>+</mo> </mrow> </msup> </mrow> </mrow> </msub> <mo stretchy="false">)</mo> <mo>=</mo> <msup> <mi>E</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>0</mn> </mrow> </msup> <mo>−</mo> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <mrow> <mi>R</mi> <mi>T</mi> <mtext> </mtext> <mi>ln</mi> <mo>⁡</mo> <mrow class="MJX-TeXAtom-ORD"> <mn>10</mn> </mrow> </mrow> <mi>F</mi> </mfrac> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mtext>pH</mtext> </mrow> <mo>≈</mo> <msup> <mi>E</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>0</mn> </mrow> </msup> <mo>−</mo> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <mrow> <mn>2.303</mn> <mtext> </mtext> <mi>R</mi> <mi>T</mi> </mrow> <mi>F</mi> </mfrac> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mtext>pH</mtext> </mrow> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle E=E^{0}+{\frac {RT}{F}}\ln(a_{{\ce {H+}}})=E^{0}-{\frac {RT\ \ln {10}}{F}}{\ce {pH}}\approx E^{0}-{\frac {2.303\ RT}{F}}{\ce {pH}}}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/52baacfee9e6ff5c415c2194743c1c96d5050834" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -1.838ex; width:66.446ex; height:5.343ex;" alt="{\displaystyle E=E^{0}+{\frac {RT}{F}}\ln(a_{{\ce {H+}}})=E^{0}-{\frac {RT\ \ln {10}}{F}}{\ce {pH}}\approx E^{0}-{\frac {2.303\ RT}{F}}{\ce {pH}}}"></span></dd></dl> <p>where <i>E</i> is a measured potential, <i>E</i><sup>0</sup> is the standard electrode potential, <i>R</i> is the <a href="/wiki/Molar_gas_constant" class="mw-redirect" title="Molar gas constant">molar gas constant</a>, <i>T</i> is the thermodynamic temperature, <i>F</i> is the <a href="/wiki/Faraday_constant" title="Faraday constant">Faraday constant</a>. For <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">H<sup class="template-chem2-sup">+</sup></span>, the number of electrons transferred is one. The electrode potential is proportional to pH when pH is defined in terms of activity. </p><p>The precise measurement of pH is presented in International Standard <a href="/wiki/ISO_31-8" title="ISO 31-8">ISO 31-8</a> as follows:<sup id="cite_ref-15" class="reference"><a href="#cite_note-15"><span class="cite-bracket">[</span>15<span class="cite-bracket">]</span></a></sup> A <a href="/wiki/Galvanic_cell" title="Galvanic cell">galvanic cell</a> is set up to measure the <a href="/wiki/Electromotive_force" title="Electromotive force">electromotive force</a> (e.m.f.) between a reference electrode and an electrode sensitive to the hydrogen ion activity when they are both immersed in the same aqueous solution. The reference electrode may be a <a href="/wiki/Silver_chloride_electrode" title="Silver chloride electrode">silver chloride electrode</a> or a <a href="/wiki/Saturated_calomel_electrode" title="Saturated calomel electrode">calomel electrode</a>, and the hydrogen-ion selective electrode is a <a href="/wiki/Standard_hydrogen_electrode" title="Standard hydrogen electrode">standard hydrogen electrode</a>. </p> <dl><dd><span class="texhtml">Reference electrode | concentrated solution of KCl || test solution | H<sub>2</sub> | Pt</span></dd></dl> <p>Firstly, the cell is filled with a solution of known hydrogen ion activity and the electromotive force, <i>E</i><sub>S</sub>, is measured. Then the electromotive force, <i>E</i><sub>X</sub>, of the same cell containing the solution of unknown pH is measured. </p> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle {\ce {pH(X)}}={\ce {pH(S)}}+{\frac {E_{{\ce {S}}}-E_{{\ce {X}}}}{z}}}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mrow class="MJX-TeXAtom-ORD"> <mtext>pH</mtext> <mrow class="MJX-TeXAtom-ORD"> <mo stretchy="false">(</mo> <mtext>X</mtext> <mo stretchy="false">)</mo> </mrow> </mrow> <mo>=</mo> <mrow class="MJX-TeXAtom-ORD"> <mtext>pH</mtext> <mrow class="MJX-TeXAtom-ORD"> <mo stretchy="false">(</mo> <mtext>S</mtext> <mo stretchy="false">)</mo> </mrow> </mrow> <mo>+</mo> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <mrow> <msub> <mi>E</mi> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-ORD"> <mtext>S</mtext> </mrow> </mrow> </msub> <mo>−</mo> <msub> <mi>E</mi> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-ORD"> <mtext>X</mtext> </mrow> </mrow> </msub> </mrow> <mi>z</mi> </mfrac> </mrow> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle {\ce {pH(X)}}={\ce {pH(S)}}+{\frac {E_{{\ce {S}}}-E_{{\ce {X}}}}{z}}}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/61d7f14649cf22c1e0a8f70a165821e5367fa721" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -1.838ex; width:28.382ex; height:5.343ex;" alt="{\displaystyle {\ce {pH(X)}}={\ce {pH(S)}}+{\frac {E_{{\ce {S}}}-E_{{\ce {X}}}}{z}}}"></span></dd></dl> <p>The difference between the two measured electromotive force values is proportional to pH. This method of calibration avoids the need to know the <a href="/wiki/Standard_electrode_potential" title="Standard electrode potential">standard electrode potential</a>. The proportionality constant, 1/<i>z</i>, is ideally equal to <span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle {\frac {F}{RT\ln {10}}}\ }"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <mi>F</mi> <mrow> <mi>R</mi> <mi>T</mi> <mi>ln</mi> <mo>⁡</mo> <mrow class="MJX-TeXAtom-ORD"> <mn>10</mn> </mrow> </mrow> </mfrac> </mrow> <mtext> </mtext> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle {\frac {F}{RT\ln {10}}}\ }</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/da90052e3fc4ff151c53de27ac3d0802bb2f50bb" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -2.005ex; width:9.856ex; height:5.343ex;" alt="{\displaystyle {\frac {F}{RT\ln {10}}}\ }"></span>, the "Nernstian slope". </p><p>In practice, a <a href="/wiki/Glass_electrode" title="Glass electrode">glass electrode</a> is used instead of the cumbersome hydrogen electrode. A combined glass electrode has an in-built reference electrode. It is calibrated against <a href="/wiki/Buffer_solution" title="Buffer solution">Buffer solutions</a> of known hydrogen ion (<link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">H<sup class="template-chem2-sup">+</sup></span>) activity proposed by the International Union of Pure and Applied Chemistry (<a href="/wiki/IUPAC" class="mw-redirect" title="IUPAC">IUPAC</a>).<sup id="cite_ref-covington3_3-2" class="reference"><a href="#cite_note-covington3-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> Two or more buffer solutions are used in order to accommodate the fact that the "slope" may differ slightly from ideal. To calibrate the electrode, it is first immersed in a standard solution, and the reading on a <a href="/wiki/PH_meter" title="PH meter">pH meter</a> is adjusted to be equal to the standard buffer's value. The reading from a second standard buffer solution is then adjusted using the "slope" control to be equal to the pH for that solution. Further details, are given in the <a href="/wiki/IUPAC" class="mw-redirect" title="IUPAC">IUPAC</a> recommendations.<sup id="cite_ref-covington22_16-0" class="reference"><a href="#cite_note-covington22-16"><span class="cite-bracket">[</span>16<span class="cite-bracket">]</span></a></sup> When more than two buffer solutions are used the electrode is calibrated by fitting observed pH values to a straight line with respect to standard buffer values. Commercial standard buffer solutions usually come with information on the value at 25 °C and a correction factor to be applied for other temperatures. </p><p>The pH scale is logarithmic and therefore pH is a <a href="/wiki/Dimensionless_quantity" title="Dimensionless quantity">dimensionless quantity</a>.<sup id="cite_ref-17" class="reference"><a href="#cite_note-17"><span class="cite-bracket">[</span>17<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="p[H]"><span id="p.5BH.5D"></span>p[H]</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=PH&action=edit&section=4" title="Edit section: p[H]"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>This was the original definition of Sørensen in 1909,<sup id="cite_ref-Sor2_18-0" class="reference"><a href="#cite_note-Sor2-18"><span class="cite-bracket">[</span>18<span class="cite-bracket">]</span></a></sup> which was superseded in favor of pH in 1924. [H] is the concentration of hydrogen ions, denoted [<link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">H<sup>+</sup></span>] in modern chemistry. More correctly, the <a href="/wiki/Thermodynamic_activity" title="Thermodynamic activity">thermodynamic activity</a> of <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">H<sup>+</sup></span> in dilute solution should be replaced by [<link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">H<sup>+</sup></span>]/<i>c</i><sub>0</sub>, where the standard state concentration <i>c</i><sub>0</sub> = 1 mol/L. This ratio is a pure number whose logarithm can be defined. </p><p>It is possible to measure the concentration of hydrogen ions directly using an electrode calibrated in terms of hydrogen ion concentrations. One common method is to <a href="/wiki/Titration" title="Titration">titrate</a> a solution of known concentration of a strong acid with a solution of known concentration of strong base in the presence of a relatively high concentration of background electrolyte. By knowing the concentrations of the acid and base, the concentration of hydrogen ions can be calculated and the measured potential can be correlated with concentrations. The calibration is usually carried out using a <a href="/wiki/Gran_plot#Electrode_calibration" title="Gran plot">Gran plot</a>.<sup id="cite_ref-19" class="reference"><a href="#cite_note-19"><span class="cite-bracket">[</span>19<span class="cite-bracket">]</span></a></sup> This procedure makes the activity of hydrogen ions equal to the numerical value of concentration. </p><p>The glass electrode (and other <a href="/wiki/Ion_selective_electrode" class="mw-redirect" title="Ion selective electrode">Ion selective electrodes</a>) should be calibrated in a medium similar to the one being investigated. For instance, if one wishes to measure the pH of a seawater sample, the electrode should be calibrated in a solution resembling seawater in its chemical composition. </p><p>The difference between p[H] and pH is quite small, and it has been stated that pH = p[H] + 0.04.<sup id="cite_ref-20" class="reference"><a href="#cite_note-20"><span class="cite-bracket">[</span>20<span class="cite-bracket">]</span></a></sup> However, it is common practice to use the term "pH" for both types of measurement. </p> <div class="mw-heading mw-heading3"><h3 id="pOH">pOH</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=PH&action=edit&section=5" title="Edit section: pOH"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:PHscalenolang.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/b/bb/PHscalenolang.svg/220px-PHscalenolang.svg.png" decoding="async" width="220" height="62" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/b/bb/PHscalenolang.svg/330px-PHscalenolang.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/b/bb/PHscalenolang.svg/440px-PHscalenolang.svg.png 2x" data-file-width="731" data-file-height="205" /></a><figcaption>Relation between pH and pOH. Red represents the acidic region. Blue represents the basic region.</figcaption></figure> <p>pOH is sometimes used as a measure of the concentration of hydroxide ions, <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">OH<sup class="template-chem2-sup">−</sup></span>. By definition, pOH is the negative logarithm (to the base 10) of the hydroxide ion concentration (mol/L). pOH values can be derived from pH measurements and vice-versa. The concentration of hydroxide ions in water is related to the concentration of hydrogen ions by </p> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle [{\ce {OH^-}}]={\frac {K_{{\ce {W}}}}{[{\ce {H^+}}]}}}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mo stretchy="false">[</mo> <mrow class="MJX-TeXAtom-ORD"> <msup> <mtext>OH</mtext> <mrow class="MJX-TeXAtom-ORD"> <mo>−</mo> </mrow> </msup> </mrow> <mo stretchy="false">]</mo> <mo>=</mo> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <msub> <mi>K</mi> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-ORD"> <mtext>W</mtext> </mrow> </mrow> </msub> <mrow> <mo stretchy="false">[</mo> <mrow class="MJX-TeXAtom-ORD"> <msup> <mtext>H</mtext> <mrow class="MJX-TeXAtom-ORD"> <mo>+</mo> </mrow> </msup> </mrow> <mo stretchy="false">]</mo> </mrow> </mfrac> </mrow> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle [{\ce {OH^-}}]={\frac {K_{{\ce {W}}}}{[{\ce {H^+}}]}}}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/0e914d2d8665e01b649b6ecc09acdb2bb823b33c" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -2.838ex; width:14.838ex; height:6.343ex;" alt="{\displaystyle [{\ce {OH^-}}]={\frac {K_{{\ce {W}}}}{[{\ce {H^+}}]}}}"></span></dd></dl> <p>where <i>K</i><sub>W</sub> is the <a href="/wiki/Self-ionization_of_water" title="Self-ionization of water">self-ionization</a> constant of water. Taking <a href="/wiki/Logarithm" title="Logarithm">Logarithms</a>, </p> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle {\ce {pOH}}={\ce {p}}K_{{\ce {W}}}-{\ce {pH}}.}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mrow class="MJX-TeXAtom-ORD"> <mtext>pOH</mtext> </mrow> <mo>=</mo> <mrow class="MJX-TeXAtom-ORD"> <mtext>p</mtext> </mrow> <msub> <mi>K</mi> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-ORD"> <mtext>W</mtext> </mrow> </mrow> </msub> <mo>−</mo> <mrow class="MJX-TeXAtom-ORD"> <mtext>pH</mtext> </mrow> <mo>.</mo> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle {\ce {pOH}}={\ce {p}}K_{{\ce {W}}}-{\ce {pH}}.}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/759d32a09b7693aeef989fecebaa74adce9da236" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.671ex; width:19.652ex; height:2.509ex;" alt="{\displaystyle {\ce {pOH}}={\ce {p}}K_{{\ce {W}}}-{\ce {pH}}.}"></span></dd></dl> <p>So, at room temperature, pOH ≈ 14 − pH. However this relationship is not strictly valid in other circumstances, such as in measurements of <a href="/wiki/Alkaline_soils" class="mw-redirect" title="Alkaline soils">soil alkalinity</a>. </p> <div class="mw-heading mw-heading2"><h2 id="Measurement">Measurement</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=PH&action=edit&section=6" title="Edit section: Measurement"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <div class="mw-heading mw-heading3"><h3 id="pH_Indicators">pH Indicators</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=PH&action=edit&section=7" title="Edit section: pH Indicators"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <table class="wikitable floatright"> <caption>Average pH of common solutions </caption> <tbody><tr> <th>Substance </th> <th>pH range </th> <th>Type </th></tr> <tr> <td><a href="/wiki/Sulfuric_acid" title="Sulfuric acid">Battery acid</a> </td> <td style="background-color: #CC0000; text-align: center; color: #ffffff">< 1 </td> <td rowspan="6" style="text-align: center"><a href="/wiki/Acid" title="Acid">Acid</a> </td></tr> <tr> <td><a href="/wiki/Gastric_acid" title="Gastric acid">Gastric acid</a> </td> <td style="background-color: #EE0000; text-align: center; color: #ffffff">1.0–1.5 </td></tr> <tr> <td><a href="/wiki/Vinegar" title="Vinegar">Vinegar</a> </td> <td style="background-color: #FF4000; text-align: center">2–3 </td></tr> <tr> <td><a href="/wiki/Orange_juice" title="Orange juice">Orange juice</a> </td> <td style="background-color: #FF6600; text-align: center">3.3–4.2 </td></tr> <tr> <td><a href="/wiki/Coffee" title="Coffee">Black coffee</a> </td> <td style="background-color: #ffff00 ; text-align: center">5–5.03 </td></tr> <tr> <td><a href="/wiki/Milk" title="Milk">Milk</a> </td> <td style="background-color: #99cc33; text-align: center">6.5–6.8 </td></tr> <tr> <td><a href="/wiki/Pure_water" class="mw-redirect" title="Pure water">Pure water</a> at 25 °C </td> <td style="background-color: #339933; text-align: center; color: #ffffff">7 </td> <td style="text-align: center">Neutral </td></tr> <tr> <td><a href="/wiki/Sea_water" class="mw-redirect" title="Sea water">Sea water</a> </td> <td style="background-color: #19cdff; text-align: center; color: #000000">7.5–8.4 </td> <td rowspan="4" style="text-align: center"><a href="/wiki/Base_(chemistry)" title="Base (chemistry)">Base</a> </td></tr> <tr> <td><a href="/wiki/Ammonia" title="Ammonia">Ammonia</a> </td> <td style="background-color: #3333ff; text-align: center; color: #FFFFFF">11.0–11.5 </td></tr> <tr> <td><a href="/wiki/Bleach" title="Bleach">Bleach</a> </td> <td style="background-color: #330099; text-align: center; color: #FFFFFF">12.5 </td></tr> <tr> <td><a href="/wiki/Lye" title="Lye">Lye</a> </td> <td style="background-color: #330066; text-align: center; color: #FFFFFF">14 </td></tr></tbody></table> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/PH_indicator" title="PH indicator">pH indicator</a></div> <p>pH can be measured using indicators, which change color depending on the pH of the solution they are in. By comparing the color of a test solution to a standard color chart, the pH can be estimated to the nearest whole number. For more precise measurements, the color can be measured using a <a href="/wiki/Colorimeter_(chemistry)" title="Colorimeter (chemistry)">colorimeter</a> or <a href="/wiki/Spectrophotometer" class="mw-redirect" title="Spectrophotometer">spectrophotometer</a>. A <a href="/wiki/Universal_indicator" title="Universal indicator">Universal indicator</a> is a mixture of several indicators that can provide a continuous color change over a range of pH values, typically from about pH 2 to pH 10. Universal indicator paper is made from absorbent paper that has been impregnated with a universal indicator. An alternative method of measuring pH is using an electronic <a href="/wiki/PH_meter" title="PH meter">pH meter</a>, which directly measures the voltage difference between a pH-sensitive electrode and a reference electrode. </p> <div class="mw-heading mw-heading3"><h3 id="Non-aqueous_solutions">Non-aqueous solutions</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=PH&action=edit&section=8" title="Edit section: Non-aqueous solutions"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>pH values can be measured in non-aqueous solutions, but they are based on a different scale from aqueous pH values because the <a href="/wiki/Standard_state" title="Standard state">standard states</a> used for calculating hydrogen ion concentrations (<a href="/wiki/Activity_(chemistry)" class="mw-redirect" title="Activity (chemistry)">activities</a>) are different. The hydrogen ion activity, <i>a</i><sub>H<sup>+</sup></sub>, is defined<sup id="cite_ref-GoldBook2_21-0" class="reference"><a href="#cite_note-GoldBook2-21"><span class="cite-bracket">[</span>21<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-GreenBook2_22-0" class="reference"><a href="#cite_note-GreenBook2-22"><span class="cite-bracket">[</span>22<span class="cite-bracket">]</span></a></sup> as: </p> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle a_{{\ce {H+}}}=\exp \left({\frac {\mu _{{\ce {H+}}}-\mu _{{\ce {H+}}}^{\ominus }}{RT}}\right)}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <msub> <mi>a</mi> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-ORD"> <msup> <mtext>H</mtext> <mrow class="MJX-TeXAtom-ORD"> <mo>+</mo> </mrow> </msup> </mrow> </mrow> </msub> <mo>=</mo> <mi>exp</mi> <mo>⁡</mo> <mrow> <mo>(</mo> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <mrow> <msub> <mi>μ</mi> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-ORD"> <msup> <mtext>H</mtext> <mrow class="MJX-TeXAtom-ORD"> <mo>+</mo> </mrow> </msup> </mrow> </mrow> </msub> <mo>−</mo> <msubsup> <mi>μ</mi> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-ORD"> <msup> <mtext>H</mtext> <mrow class="MJX-TeXAtom-ORD"> <mo>+</mo> </mrow> </msup> </mrow> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mo>⊖</mo> </mrow> </msubsup> </mrow> <mrow> <mi>R</mi> <mi>T</mi> </mrow> </mfrac> </mrow> <mo>)</mo> </mrow> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle a_{{\ce {H+}}}=\exp \left({\frac {\mu _{{\ce {H+}}}-\mu _{{\ce {H+}}}^{\ominus }}{RT}}\right)}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/c2554db9edcefbf9fbe64b965caf52d88fbef11c" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -3.171ex; width:26.043ex; height:7.509ex;" alt="{\displaystyle a_{{\ce {H+}}}=\exp \left({\frac {\mu _{{\ce {H+}}}-\mu _{{\ce {H+}}}^{\ominus }}{RT}}\right)}"></span></dd></dl> <p>where <i>μ</i><sub>H<sup>+</sup></sub> is the <a href="/wiki/Chemical_potential" title="Chemical potential">chemical potential</a> of the hydrogen ion, <span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle \mu _{{\ce {H+}}}^{\ominus }}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <msubsup> <mi>μ</mi> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-ORD"> <msup> <mtext>H</mtext> <mrow class="MJX-TeXAtom-ORD"> <mo>+</mo> </mrow> </msup> </mrow> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mo>⊖</mo> </mrow> </msubsup> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle \mu _{{\ce {H+}}}^{\ominus }}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/4b94d142b00deab67cbdaa710bcd956bb12cc916" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -1.338ex; width:4.069ex; height:3.509ex;" alt="{\displaystyle \mu _{{\ce {H+}}}^{\ominus }}"></span> is its chemical potential in the chosen standard state, <i>R</i> is the <a href="/wiki/Molar_gas_constant" class="mw-redirect" title="Molar gas constant">molar gas constant</a> and <i>T</i> is the <a href="/wiki/Thermodynamic_temperature" title="Thermodynamic temperature">thermodynamic temperature</a>. Therefore, pH values on the different scales cannot be compared directly because of differences in the solvated proton ions, such as lyonium ions, which require an insolvent scale that involves the transfer activity coefficient of <a href="/wiki/Lyonium_ion" title="Lyonium ion">hydronium/lyonium ion</a>. </p><p>pH is an example of an <a href="/wiki/Acidity_function" title="Acidity function">acidity function</a>, but others can be defined. For example, the <a href="/wiki/Hammett_acidity_function" title="Hammett acidity function">Hammett acidity function</a>, <i>H</i><sub>0</sub>, has been developed in connection with <a href="/wiki/Superacid" title="Superacid">Superacids</a>. </p> <div class="mw-heading mw-heading3"><h3 id="Unified_absolute_pH_scale">Unified absolute pH scale</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=PH&action=edit&section=9" title="Edit section: Unified absolute pH scale"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>In 2010, a new approach to measuring pH was proposed, called the <i>unified absolute pH scale</i>. This approach allows for a common reference standard to be used across different solutions, regardless of their pH range. The unified absolute pH scale is based on the absolute chemical potential of the proton, as defined by the <a href="/wiki/Lewis_acids_and_bases" title="Lewis acids and bases">Lewis acid–base</a> theory. This scale applies to liquids, gases, and even solids.<sup id="cite_ref-Krossing2_23-0" class="reference"><a href="#cite_note-Krossing2-23"><span class="cite-bracket">[</span>23<span class="cite-bracket">]</span></a></sup> The advantages of the unified absolute pH scale include consistency, accuracy, and applicability to a wide range of sample types. It is precise and versatile because it serves as a common reference standard for pH measurements. However, implementation efforts, compatibility with existing data, complexity, and potential costs are some challenges. </p> <div class="mw-heading mw-heading3"><h3 id="Extremes_of_pH_measurements">Extremes of pH measurements</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=PH&action=edit&section=10" title="Edit section: Extremes of pH measurements"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">"Negative pH" redirects here. For the band, see <a href="/wiki/Negative_pH_(band)" title="Negative pH (band)">Negative pH (band)</a>.</div> <p>The measurement of pH can become difficult at extremely acidic or alkaline conditions, such as below pH 2.5 (ca. 0.003 <a href="/wiki/Mole_(unit)" title="Mole (unit)">mol</a>/dm<sup>3</sup> acid) or above pH 10.5 (above ca. 0.0003 mol/dm<sup>3</sup> alkaline). This is due to the breakdown of the <a href="/wiki/Nernst_equation" title="Nernst equation">Nernst equation</a> in such conditions when using a glass electrode. Several factors contribute to this problem. First, <a href="/wiki/Liquid_junction_potential" title="Liquid junction potential">liquid junction potentials</a> may not be independent of pH.<sup id="cite_ref-Feldman2_24-0" class="reference"><a href="#cite_note-Feldman2-24"><span class="cite-bracket">[</span>24<span class="cite-bracket">]</span></a></sup> Second, the high <a href="/wiki/Ionic_strength" title="Ionic strength">ionic strength</a> of concentrated solutions can affect the electrode potentials. At high pH the glass electrode may be affected by "alkaline error", because the electrode becomes sensitive to the concentration of cations such as <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">Na<sup class="template-chem2-sup">+</sup></span> and <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">K<sup class="template-chem2-sup">+</sup></span> in the solution.<sup id="cite_ref-25" class="reference"><a href="#cite_note-25"><span class="cite-bracket">[</span>25<span class="cite-bracket">]</span></a></sup> To overcome these problems, specially constructed electrodes are available. </p><p>Runoff from mines or mine tailings can produce some extremely low pH values, down to −3.6.<sup id="cite_ref-26" class="reference"><a href="#cite_note-26"><span class="cite-bracket">[</span>26<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="Applications">Applications</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=PH&action=edit&section=11" title="Edit section: Applications"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Pure water has a pH of 7 at 25 °C, meaning it is neutral. When an <a href="/wiki/Acid" title="Acid">acid</a> is dissolved in water, the pH will be less than 7, while a <a href="/wiki/Base_(chemistry)" title="Base (chemistry)">base</a>, or <a href="/wiki/Alkali" title="Alkali">alkali</a>, will have a pH greater than 7. A strong acid, such as <a href="/wiki/Hydrochloric_acid" title="Hydrochloric acid">hydrochloric acid</a>, at concentration 1 mol dm<sup>−3</sup> has a pH of 0, while a strong alkali like <a href="/wiki/Sodium_hydroxide" title="Sodium hydroxide">sodium hydroxide</a>, at the same concentration, has a pH of 14. Since pH is a logarithmic scale, a difference of one in pH is equivalent to a tenfold difference in hydrogen ion concentration. </p><p>Neutrality is not exactly 7 at 25 °C, but 7 serves as a good approximation in most cases. Neutrality occurs when the concentration of hydrogen ions ([<link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">H<sup class="template-chem2-sup">+</sup></span>]) equals the concentration of hydroxide ions ([<link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">OH<sup class="template-chem2-sup">−</sup></span>]), or when their activities are equal. Since <a href="/wiki/Self-ionization_of_water" title="Self-ionization of water">self-ionization of water</a> holds the product of these concentration [<link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">H<sup class="template-chem2-sup">+</sup></span>] × [<link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">OH<sup class="template-chem2-sup">−</sup></span>] = <i>K</i><sub>w</sub>, it can be seen that at neutrality [<link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">H<sup class="template-chem2-sup">+</sup></span>] = [<link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">OH<sup class="template-chem2-sup">−</sup></span>] = <span class="nowrap">√<span style="border-top:1px solid; padding:0 0.1em;"><i>K</i><sub>w</sub></span></span>, or pH = p<i>K</i><sub>w</sub>/2. p<i>K</i><sub>w</sub> is approximately 14 but depends on ionic strength and temperature, and so the pH of neutrality does also. Pure water and a solution of <a href="/wiki/Sodium_chloride" title="Sodium chloride">NaCl</a> in pure water are both neutral, since <a href="/wiki/Self-ionization_of_water" title="Self-ionization of water">dissociation of water</a> produces equal numbers of both ions. However the pH of the neutral NaCl solution will be slightly different from that of neutral pure water because the hydrogen and hydroxide ions' activity is dependent on <a href="/wiki/Ionic_strength" title="Ionic strength">ionic strength</a>, so <i>K</i><sub>w</sub> varies with ionic strength. </p><p>When pure water is exposed to air, it becomes mildly acidic. This is because water absorbs <a href="/wiki/Carbon_dioxide" title="Carbon dioxide">carbon dioxide</a> from the air, which is then slowly converted into <a href="/wiki/Bicarbonate" title="Bicarbonate">bicarbonate</a> and hydrogen ions (essentially creating <a href="/wiki/Carbonic_acid" title="Carbonic acid">carbonic acid</a>). </p> <dl><dd><span class="chemf nowrap">CO<span class="nowrap"><span style="display:inline-block;margin-bottom:-0.3em;vertical-align:-0.4em;line-height:1em;font-size:80%;text-align:left"><sup style="font-size:inherit;line-height:inherit;vertical-align:baseline"></sup><br /><sub style="font-size:inherit;line-height:inherit;vertical-align:baseline">2</sub></span></span>+ H<span class="nowrap"><span style="display:inline-block;margin-bottom:-0.3em;vertical-align:-0.4em;line-height:1em;font-size:80%;text-align:left"><sup style="font-size:inherit;line-height:inherit;vertical-align:baseline"></sup><br /><sub style="font-size:inherit;line-height:inherit;vertical-align:baseline">2</sub></span></span>O ⇌ HCO<span class="nowrap"><span style="display:inline-block;margin-bottom:-0.3em;vertical-align:-0.4em;line-height:1em;font-size:80%;text-align:left"><sup style="font-size:inherit;line-height:inherit;vertical-align:baseline">−</sup><br /><sub style="font-size:inherit;line-height:inherit;vertical-align:baseline">3</sub></span></span>+ H<span class="nowrap"><span style="display:inline-block;margin-bottom:-0.3em;vertical-align:0.8em;line-height:1em;font-size:80%;text-align:left"><sup style="font-size:inherit;line-height:inherit;vertical-align:baseline">+</sup><br /><sub style="font-size:inherit;line-height:inherit;vertical-align:baseline"></sub></span></span></span></dd></dl> <div class="mw-heading mw-heading3"><h3 id="pH_in_soil">pH in soil</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=PH&action=edit&section=12" title="Edit section: pH in soil"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">See also: <a href="/wiki/Soil_pH" title="Soil pH">Soil pH</a></div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Soil_pH_effect_on_nutrient_availability.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/a/a3/Soil_pH_effect_on_nutrient_availability.svg/220px-Soil_pH_effect_on_nutrient_availability.svg.png" decoding="async" width="220" height="193" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/a/a3/Soil_pH_effect_on_nutrient_availability.svg/330px-Soil_pH_effect_on_nutrient_availability.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/a/a3/Soil_pH_effect_on_nutrient_availability.svg/440px-Soil_pH_effect_on_nutrient_availability.svg.png 2x" data-file-width="512" data-file-height="448" /></a><figcaption>Nutritional elements availability within soil varies with pH. Light blue color represents the ideal range for most plants.</figcaption></figure> <p>The United States Department of Agriculture <a href="/wiki/Natural_Resources_Conservation_Service" title="Natural Resources Conservation Service">Natural Resources Conservation Service</a>, formerly Soil Conservation Service classifies <a href="/wiki/Soil_pH" title="Soil pH">soil pH</a> ranges as follows:<sup id="cite_ref-27" class="reference"><a href="#cite_note-27"><span class="cite-bracket">[</span>27<span class="cite-bracket">]</span></a></sup> <style data-mw-deduplicate="TemplateStyles:r1275448275">.mw-parser-output .defaultleft{text-align:left}.mw-parser-output .defaultcenter{text-align:center}.mw-parser-output .defaultright{text-align:right}.mw-parser-output .col1left td:nth-child(1),.mw-parser-output .col2left td:nth-child(2),.mw-parser-output .col3left td:nth-child(3),.mw-parser-output .col4left td:nth-child(4),.mw-parser-output .col5left td:nth-child(5),.mw-parser-output .col6left td:nth-child(6),.mw-parser-output .col7left td:nth-child(7),.mw-parser-output .col8left td:nth-child(8),.mw-parser-output .col9left td:nth-child(9),.mw-parser-output .col10left td:nth-child(10),.mw-parser-output .col11left td:nth-child(11),.mw-parser-output .col12left td:nth-child(12),.mw-parser-output .col13left td:nth-child(13),.mw-parser-output .col14left td:nth-child(14),.mw-parser-output .col15left td:nth-child(15),.mw-parser-output .col16left td:nth-child(16),.mw-parser-output .col17left td:nth-child(17),.mw-parser-output .col18left td:nth-child(18),.mw-parser-output .col19left td:nth-child(19),.mw-parser-output .col20left td:nth-child(20),.mw-parser-output .col21left td:nth-child(21),.mw-parser-output .col22left td:nth-child(22),.mw-parser-output .col23left td:nth-child(23),.mw-parser-output .col24left td:nth-child(24),.mw-parser-output .col25left td:nth-child(25),.mw-parser-output .col26left td:nth-child(26),.mw-parser-output .col27left td:nth-child(27),.mw-parser-output .col28left td:nth-child(28),.mw-parser-output .col29left td:nth-child(29){text-align:left}.mw-parser-output .col1center td:nth-child(1),.mw-parser-output .col2center td:nth-child(2),.mw-parser-output .col3center td:nth-child(3),.mw-parser-output .col4center td:nth-child(4),.mw-parser-output .col5center td:nth-child(5),.mw-parser-output .col6center td:nth-child(6),.mw-parser-output .col7center td:nth-child(7),.mw-parser-output .col8center td:nth-child(8),.mw-parser-output .col9center td:nth-child(9),.mw-parser-output .col10center td:nth-child(10),.mw-parser-output .col11center td:nth-child(11),.mw-parser-output .col12center td:nth-child(12),.mw-parser-output .col13center td:nth-child(13),.mw-parser-output .col14center td:nth-child(14),.mw-parser-output .col15center td:nth-child(15),.mw-parser-output .col16center td:nth-child(16),.mw-parser-output .col17center td:nth-child(17),.mw-parser-output .col18center td:nth-child(18),.mw-parser-output .col19center td:nth-child(19),.mw-parser-output .col20center td:nth-child(20),.mw-parser-output .col21center td:nth-child(21),.mw-parser-output .col22center td:nth-child(22),.mw-parser-output .col23center td:nth-child(23),.mw-parser-output .col24center td:nth-child(24),.mw-parser-output .col25center td:nth-child(25),.mw-parser-output .col26center td:nth-child(26),.mw-parser-output .col27center td:nth-child(27),.mw-parser-output .col28center td:nth-child(28),.mw-parser-output .col29center td:nth-child(29){text-align:center}.mw-parser-output .col1right td:nth-child(1),.mw-parser-output .col2right td:nth-child(2),.mw-parser-output .col3right td:nth-child(3),.mw-parser-output .col4right td:nth-child(4),.mw-parser-output .col5right td:nth-child(5),.mw-parser-output .col6right td:nth-child(6),.mw-parser-output .col7right td:nth-child(7),.mw-parser-output .col8right td:nth-child(8),.mw-parser-output .col9right td:nth-child(9),.mw-parser-output .col10right td:nth-child(10),.mw-parser-output .col11right td:nth-child(11),.mw-parser-output .col12right td:nth-child(12),.mw-parser-output .col13right td:nth-child(13),.mw-parser-output .col14right td:nth-child(14),.mw-parser-output .col15right td:nth-child(15),.mw-parser-output .col16right td:nth-child(16),.mw-parser-output .col17right td:nth-child(17),.mw-parser-output .col18right td:nth-child(18),.mw-parser-output .col19right td:nth-child(19),.mw-parser-output .col20right td:nth-child(20),.mw-parser-output .col21right td:nth-child(21),.mw-parser-output .col22right td:nth-child(22),.mw-parser-output .col23right td:nth-child(23),.mw-parser-output .col24right td:nth-child(24),.mw-parser-output .col25right td:nth-child(25),.mw-parser-output .col26right td:nth-child(26),.mw-parser-output .col27right td:nth-child(27),.mw-parser-output .col28right td:nth-child(28),.mw-parser-output .col29right td:nth-child(29){text-align:right}</style> </p> <table class="wikitable defaultright"> <tbody><tr> <th scope="col">Denomination </th> <th scope="col">pH range </th></tr> <tr> <td>Ultra acidic </td> <td>< 3.5 </td></tr> <tr> <td>Extremely acidic </td> <td>3.5–4.4 </td></tr> <tr> <td>Very strongly acidic </td> <td>4.5–5.0 </td></tr> <tr> <td>Strongly acidic </td> <td>5.1–5.5 </td></tr> <tr> <td>Moderately acidic </td> <td>5.6–6.0 </td></tr> <tr> <td>Slightly acidic </td> <td>6.1–6.5 </td></tr> <tr> <td>Neutral </td> <td>6.6–7.3 </td></tr> <tr> <td>Slightly alkaline </td> <td>7.4–7.8 </td></tr> <tr> <td>Moderately alkaline </td> <td>7.9–8.4 </td></tr> <tr> <td>Strongly alkaline </td> <td>8.5–9.0 </td></tr> <tr> <td>Very strongly alkaline </td> <td>9.0–10.5 </td></tr> <tr> <td>Hyper alkaline </td> <td>> 10.5 </td></tr></tbody></table> <p>Topsoil pH is influenced by soil parent material, erosional effects, climate and vegetation. A recent map<sup id="cite_ref-28" class="reference"><a href="#cite_note-28"><span class="cite-bracket">[</span>28<span class="cite-bracket">]</span></a></sup> of topsoil pH in Europe shows the alkaline soils in Mediterranean, Hungary, East Romania, North France. Scandinavian countries, Portugal, Poland and North Germany have more acid soils. </p> <div class="mw-heading mw-heading3"><h3 id="pH_in_plants">pH in plants</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=PH&action=edit&section=13" title="Edit section: pH in plants"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Lemon_-_whole_and_split.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/f/f7/Lemon_-_whole_and_split.jpg/220px-Lemon_-_whole_and_split.jpg" decoding="async" width="220" height="147" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/f/f7/Lemon_-_whole_and_split.jpg/330px-Lemon_-_whole_and_split.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/f/f7/Lemon_-_whole_and_split.jpg/440px-Lemon_-_whole_and_split.jpg 2x" data-file-width="6000" data-file-height="4000" /></a><figcaption><a href="/wiki/Lemon_juice" class="mw-redirect" title="Lemon juice">Lemon juice</a> tastes sour because it contains 5% to 6% <a href="/wiki/Citric_acid" title="Citric acid">citric acid</a> and has a pH of 2.2 (high acidity).</figcaption></figure> <p>Plants contain pH-dependent <a href="/wiki/Plant_pigment" class="mw-redirect" title="Plant pigment">pigments</a> that can be used as <a href="/wiki/PH_indicator" title="PH indicator">pH indicators</a>, such as those found in <a href="/wiki/Hibiscus" title="Hibiscus">hibiscus</a>, <a href="/wiki/Red_cabbage" title="Red cabbage">red cabbage</a> (<a href="/wiki/Anthocyanin" title="Anthocyanin">anthocyanin</a>), and grapes (<a href="/wiki/Red_wine" title="Red wine">red wine</a>). <a href="/wiki/Citrus" title="Citrus">Citrus</a> fruits have acidic juice primarily due to the presence of <a href="/wiki/Citric_acid" title="Citric acid">citric acid</a>, while other <a href="/wiki/Carboxylic_acid" title="Carboxylic acid">carboxylic acids</a> can be found in various living systems. The <a href="/wiki/Protonation" title="Protonation">protonation</a> state of <a href="/wiki/Phosphate" title="Phosphate">phosphate</a> derivatives, including <a href="/wiki/Adenosine_triphosphate" title="Adenosine triphosphate">ATP</a>, is pH-dependent. <a href="/wiki/Hemoglobin" title="Hemoglobin">Hemoglobin</a>, an oxygen-transport enzyme, is also affected by pH in a phenomenon known as the <a href="/wiki/Root_effect" title="Root effect">Root effect</a>. </p> <div class="mw-heading mw-heading3"><h3 id="pH_in_the_ocean">pH in the ocean</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=PH&action=edit&section=14" title="Edit section: pH in the ocean"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p><span class="anchor" id="Seawater"></span><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"></p><div role="note" class="hatnote navigation-not-searchable">See also: <a href="/wiki/Seawater#pH_value" title="Seawater">Seawater § pH value</a>, <a href="/wiki/Ocean#pH_and_alkalinity" title="Ocean">Ocean § pH and alkalinity</a>, and <a href="/wiki/Ocean_acidification" title="Ocean acidification">Ocean acidification</a></div> <p>The pH of <a href="/wiki/Seawater" title="Seawater">seawater</a> plays an important role in the ocean's <a href="/wiki/Carbon_cycle#Ocean" title="Carbon cycle">carbon cycle</a>. There is evidence of ongoing <a href="/wiki/Ocean_acidification" title="Ocean acidification">ocean acidification</a> (meaning a drop in pH value): Between 1950 and 2020, the average pH of the ocean surface fell from approximately 8.15 to 8.05.<sup id="cite_ref-29" class="reference"><a href="#cite_note-29"><span class="cite-bracket">[</span>29<span class="cite-bracket">]</span></a></sup> <a href="/wiki/Carbon_dioxide_emissions" class="mw-redirect" title="Carbon dioxide emissions">Carbon dioxide emissions</a> from human activities are the primary cause of ocean acidification, with <a href="/wiki/Carbon_dioxide_in_Earth%27s_atmosphere" title="Carbon dioxide in Earth's atmosphere">atmospheric carbon dioxide (CO<sub>2</sub>) levels</a> exceeding 410 ppm (in 2020). CO<sub>2</sub> from the <a href="/wiki/Atmosphere" title="Atmosphere">atmosphere</a> is absorbed by the oceans. This produces <a href="/wiki/Carbonic_acid" title="Carbonic acid">carbonic acid</a> (H<sub>2</sub>CO<sub>3</sub>) which dissociates into a <a href="/wiki/Bicarbonate_ion" class="mw-redirect" title="Bicarbonate ion">bicarbonate ion</a> (<span class="chemf nowrap">HCO<span class="nowrap"><span style="display:inline-block;margin-bottom:-0.3em;vertical-align:-0.4em;line-height:1em;font-size:80%;text-align:left"><sup style="font-size:inherit;line-height:inherit;vertical-align:baseline">−</sup><br /><sub style="font-size:inherit;line-height:inherit;vertical-align:baseline">3</sub></span></span></span>) and a <a href="/wiki/Hydrogen_ion" title="Hydrogen ion">hydrogen ion</a> (H<sup>+</sup>). The presence of free hydrogen ions (H<sup>+</sup>) lowers the pH of the ocean. </p> <div class="mw-heading mw-heading4"><h4 id="Three_pH_scales_in_oceanography">Three pH scales in oceanography</h4><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=PH&action=edit&section=15" title="Edit section: Three pH scales in oceanography"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The measurement of pH in seawater is complicated by the <a href="/wiki/Chemical_property" title="Chemical property">chemical properties</a> of seawater, and three distinct pH scales exist in <a href="/wiki/Chemical_oceanography" class="mw-redirect" title="Chemical oceanography">chemical oceanography</a>.<sup id="cite_ref-zeebe2_30-0" class="reference"><a href="#cite_note-zeebe2-30"><span class="cite-bracket">[</span>30<span class="cite-bracket">]</span></a></sup> In practical terms, the three seawater pH scales differ in their pH values up to 0.10, differences that are much larger than the accuracy of pH measurements typically required, in particular, in relation to the ocean's <a href="/wiki/Total_inorganic_carbon" title="Total inorganic carbon">carbonate system</a>.<sup id="cite_ref-zeebe2_30-1" class="reference"><a href="#cite_note-zeebe2-30"><span class="cite-bracket">[</span>30<span class="cite-bracket">]</span></a></sup> Since it omits consideration of sulfate and fluoride ions, the <i>free scale</i> is significantly different from both the total and seawater scales. Because of the relative unimportance of the fluoride ion, the total and seawater scales differ only very slightly. </p><p>As part of its <a href="/wiki/Operational_definition" title="Operational definition">operational definition</a> of the pH scale, the <a href="/wiki/IUPAC" class="mw-redirect" title="IUPAC">IUPAC</a> defines a series of <a href="/wiki/Buffer_solution" title="Buffer solution">Buffer solutions</a> across a range of pH values (often denoted with <a href="/wiki/National_Bureau_of_Standards" class="mw-redirect" title="National Bureau of Standards">National Bureau of Standards</a> (NBS) or <a href="/wiki/National_Institute_of_Standards_and_Technology" title="National Institute of Standards and Technology">National Institute of Standards and Technology</a> (NIST) designation). These solutions have a relatively low <a href="/wiki/Ionic_strength" title="Ionic strength">ionic strength</a> (≈ 0.1) compared to that of seawater (≈ 0.7), and, as a consequence, are not recommended for use in characterizing the pH of seawater, since the ionic strength differences cause changes in <a href="/wiki/Standard_electrode_potential" title="Standard electrode potential">electrode potential</a>. To resolve this problem, an alternative series of buffers based on <a href="/wiki/Artificial_seawater" title="Artificial seawater">artificial seawater</a> was developed.<sup id="cite_ref-31" class="reference"><a href="#cite_note-31"><span class="cite-bracket">[</span>31<span class="cite-bracket">]</span></a></sup> This new series resolves the problem of ionic strength differences between samples and the buffers, and the new pH scale is referred to as the <i>total scale</i>, often denoted as pH<sub>T</sub>. The total scale was defined using a medium containing <a href="/wiki/Sulfate" title="Sulfate">sulfate</a> ions. These ions experience <a href="/wiki/Protonation" title="Protonation">protonation</a>, <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">H<sup class="template-chem2-sup">+</sup></span> + <span class="chemf nowrap">SO<span class="nowrap"><span style="display:inline-block;margin-bottom:-0.3em;vertical-align:-0.4em;line-height:1em;font-size:80%;text-align:left"><sup style="font-size:inherit;line-height:inherit;vertical-align:baseline">2−</sup><br /><sub style="font-size:inherit;line-height:inherit;vertical-align:baseline">4</sub></span></span>↔ HSO<span class="nowrap"><span style="display:inline-block;margin-bottom:-0.3em;vertical-align:-0.4em;line-height:1em;font-size:80%;text-align:left"><sup style="font-size:inherit;line-height:inherit;vertical-align:baseline">−</sup><br /><sub style="font-size:inherit;line-height:inherit;vertical-align:baseline">4</sub></span></span></span>, such that the total scale includes the effect of both <a href="/wiki/Proton" title="Proton">protons</a> (free hydrogen ions) and hydrogen sulfate ions: </p> <dl><dd>[<link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">H<sup class="template-chem2-sup">+</sup></span>]<sub>T</sub> = [<link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">H<sup class="template-chem2-sup">+</sup></span>]<sub>F</sub> + [<span class="chemf nowrap">HSO<span class="nowrap"><span style="display:inline-block;margin-bottom:-0.3em;vertical-align:-0.4em;line-height:1em;font-size:80%;text-align:left"><sup style="font-size:inherit;line-height:inherit;vertical-align:baseline">−</sup><br /><sub style="font-size:inherit;line-height:inherit;vertical-align:baseline">4</sub></span></span></span>]</dd></dl> <p>An alternative scale, the <i>free scale</i>, often denoted pH<sub>F</sub>, omits this consideration and focuses solely on [<link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">H<sup class="template-chem2-sup">+</sup></span>]<sub>F</sub>, in principle making it a simpler representation of hydrogen ion concentration. Only [<link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">H<sup class="template-chem2-sup">+</sup></span>]<sub>T</sub> can be determined,<sup id="cite_ref-32" class="reference"><a href="#cite_note-32"><span class="cite-bracket">[</span>32<span class="cite-bracket">]</span></a></sup> therefore [<link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">H<sup class="template-chem2-sup">+</sup></span>]<sub>F</sub> must be estimated using the [<span class="chemf nowrap">SO<span class="nowrap"><span style="display:inline-block;margin-bottom:-0.3em;vertical-align:-0.4em;line-height:1em;font-size:80%;text-align:left"><sup style="font-size:inherit;line-height:inherit;vertical-align:baseline">2−</sup><br /><sub style="font-size:inherit;line-height:inherit;vertical-align:baseline">4</sub></span></span></span>] and the stability constant of <span class="chemf nowrap">HSO<span class="nowrap"><span style="display:inline-block;margin-bottom:-0.3em;vertical-align:-0.4em;line-height:1em;font-size:80%;text-align:left"><sup style="font-size:inherit;line-height:inherit;vertical-align:baseline">−</sup><br /><sub style="font-size:inherit;line-height:inherit;vertical-align:baseline">4</sub></span></span></span>, <span class="nowrap"><i>K</i><span class="nowrap"><span style="display:inline-block;margin-bottom:-0.3em;vertical-align:-0.4em;line-height:1.2em;font-size:80%;text-align:left"><sup style="font-size:inherit;line-height:inherit;vertical-align:baseline">*</sup><br /><sub style="font-size:inherit;line-height:inherit;vertical-align:baseline">S</sub></span></span></span>: </p> <dl><dd>[<link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">H<sup class="template-chem2-sup">+</sup></span>]<sub>F</sub> = [<link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">H<sup class="template-chem2-sup">+</sup></span>]<sub>T</sub> − [<span class="chemf nowrap">HSO<span class="nowrap"><span style="display:inline-block;margin-bottom:-0.3em;vertical-align:-0.4em;line-height:1em;font-size:80%;text-align:left"><sup style="font-size:inherit;line-height:inherit;vertical-align:baseline">−</sup><br /><sub style="font-size:inherit;line-height:inherit;vertical-align:baseline">4</sub></span></span></span>] = [<link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">H<sup class="template-chem2-sup">+</sup></span>]<sub>T</sub> ( 1 + [<span class="chemf nowrap">SO<span class="nowrap"><span style="display:inline-block;margin-bottom:-0.3em;vertical-align:-0.4em;line-height:1em;font-size:80%;text-align:left"><sup style="font-size:inherit;line-height:inherit;vertical-align:baseline">2−</sup><br /><sub style="font-size:inherit;line-height:inherit;vertical-align:baseline">4</sub></span></span></span>] / <i>K</i><span class="nowrap"><span style="display:inline-block;margin-bottom:-0.3em;vertical-align:-0.4em;line-height:1.2em;font-size:80%;text-align:left"><sup style="font-size:inherit;line-height:inherit;vertical-align:baseline">*</sup><br /><sub style="font-size:inherit;line-height:inherit;vertical-align:baseline">S</sub></span></span> )<sup>−1</sup></dd></dl> <p>However, it is difficult to estimate <i>K</i><span class="nowrap"><span style="display:inline-block;margin-bottom:-0.3em;vertical-align:-0.4em;line-height:1.2em;font-size:80%;text-align:left"><sup style="font-size:inherit;line-height:inherit;vertical-align:baseline">*</sup><br /><sub style="font-size:inherit;line-height:inherit;vertical-align:baseline">S</sub></span></span> in seawater, limiting the utility of the otherwise more straightforward free scale. </p><p>Another scale, known as the <i>seawater scale</i>, often denoted pH<sub>SWS</sub>, takes account of a further protonation relationship between hydrogen ions and <a href="/wiki/Fluoride" title="Fluoride">fluoride</a> ions, <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">H<sup class="template-chem2-sup">+</sup></span> + <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">F<sup class="template-chem2-sup">−</sup></span> ⇌ HF. Resulting in the following expression for [<link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">H<sup class="template-chem2-sup">+</sup></span>]<sub>SWS</sub>: </p> <dl><dd>[<link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">H<sup class="template-chem2-sup">+</sup></span>]<sub>SWS</sub> = [<link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">H<sup class="template-chem2-sup">+</sup></span>]<sub>F</sub> + [<span class="chemf nowrap">HSO<span class="nowrap"><span style="display:inline-block;margin-bottom:-0.3em;vertical-align:-0.4em;line-height:1em;font-size:80%;text-align:left"><sup style="font-size:inherit;line-height:inherit;vertical-align:baseline">−</sup><br /><sub style="font-size:inherit;line-height:inherit;vertical-align:baseline">4</sub></span></span></span>] + [HF]</dd></dl> <p>However, the advantage of considering this additional complexity is dependent upon the abundance of fluoride in the medium. In seawater, for instance, sulfate ions occur at much greater concentrations (> 400 times) than those of fluoride. As a consequence, for most practical purposes, the difference between the total and seawater scales is very small. </p><p>The following three equations summarize the three scales of pH: </p> <dl><dd>pH<sub>F</sub> = −log<sub>10</sub>[<link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">H<sup class="template-chem2-sup">+</sup></span>]<sub>F</sub></dd> <dd>pH<sub>T</sub> = −log<sub>10</sub>([<link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">H<sup class="template-chem2-sup">+</sup></span>]<sub>F</sub> + [<span class="chemf nowrap">HSO<span class="nowrap"><span style="display:inline-block;margin-bottom:-0.3em;vertical-align:-0.4em;line-height:1em;font-size:80%;text-align:left"><sup style="font-size:inherit;line-height:inherit;vertical-align:baseline">−</sup><br /><sub style="font-size:inherit;line-height:inherit;vertical-align:baseline">4</sub></span></span></span>]) = −log<sub>10</sub>[<link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">H<sup class="template-chem2-sup">+</sup></span>]<sub>T</sub></dd> <dd>pH<sub>SWS</sub> = −log<sub>10</sub>(<link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">H<sup class="template-chem2-sup">+</sup></span>]<sub>F</sub> + [<span class="chemf nowrap">HSO<span class="nowrap"><span style="display:inline-block;margin-bottom:-0.3em;vertical-align:-0.4em;line-height:1em;font-size:80%;text-align:left"><sup style="font-size:inherit;line-height:inherit;vertical-align:baseline">−</sup><br /><sub style="font-size:inherit;line-height:inherit;vertical-align:baseline">4</sub></span></span></span>] + [HF]) = −log<sub>10</sub>[v]<sub>SWS</sub></dd></dl> <div class="mw-heading mw-heading3"><h3 id="pH_in_food">pH in food</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=PH&action=edit&section=16" title="Edit section: pH in food"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The pH level of food influences its flavor, texture, and <a href="/wiki/Shelf_life" title="Shelf life">shelf life</a>.<sup id="cite_ref-33" class="reference"><a href="#cite_note-33"><span class="cite-bracket">[</span>33<span class="cite-bracket">]</span></a></sup> Acidic foods, such as <a href="/wiki/Citrus_fruits" class="mw-redirect" title="Citrus fruits">citrus fruits</a>, tomatoes, and <a href="/wiki/Vinegar" title="Vinegar">vinegar</a>, typically have a pH below 4.6<sup id="cite_ref-okla_34-0" class="reference"><a href="#cite_note-okla-34"><span class="cite-bracket">[</span>34<span class="cite-bracket">]</span></a></sup> with sharp and tangy taste, while basic foods taste bitter or soapy.<sup id="cite_ref-35" class="reference"><a href="#cite_note-35"><span class="cite-bracket">[</span>35<span class="cite-bracket">]</span></a></sup> Maintaining the appropriate pH in foods is essential for preventing the growth of harmful <a href="/wiki/Microorganisms" class="mw-redirect" title="Microorganisms">microorganisms</a>.<sup id="cite_ref-okla_34-1" class="reference"><a href="#cite_note-okla-34"><span class="cite-bracket">[</span>34<span class="cite-bracket">]</span></a></sup> The alkalinity of vegetables such as <a href="/wiki/Spinach" title="Spinach">spinach</a> and <a href="/wiki/Kale" title="Kale">kale</a> can also influence their texture and color during cooking.<sup id="cite_ref-36" class="reference"><a href="#cite_note-36"><span class="cite-bracket">[</span>36<span class="cite-bracket">]</span></a></sup> The pH also influences the <a href="/wiki/Maillard_reaction" title="Maillard reaction">Maillard reaction</a>, which is responsible for the browning of food during cooking, impacting both flavor and appearance.<sup id="cite_ref-37" class="reference"><a href="#cite_note-37"><span class="cite-bracket">[</span>37<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="pH_of_various_body_fluids">pH of various body fluids</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=PH&action=edit&section=17" title="Edit section: pH of various body fluids"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <dl><dd><table class="wikitable"> <caption>pH of various body fluids<sup id="cite_ref-Boron2012_38-0" class="reference"><a href="#cite_note-Boron2012-38"><span class="cite-bracket">[</span>38<span class="cite-bracket">]</span></a></sup> </caption> <tbody><tr> <th>Compartment </th> <th>pH </th></tr> <tr> <td><a href="/wiki/Gastric_acid" title="Gastric acid">Gastric acid</a></td> <td>1.5–3.5<sup id="cite_ref-39" class="reference"><a href="#cite_note-39"><span class="cite-bracket">[</span>39<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-40" class="reference"><a href="#cite_note-40"><span class="cite-bracket">[</span>40<span class="cite-bracket">]</span></a></sup> </td></tr> <tr> <td><a href="/wiki/Lysosome" title="Lysosome">Lysosomes</a></td> <td>4.5<sup id="cite_ref-Boron2012_38-1" class="reference"><a href="#cite_note-Boron2012-38"><span class="cite-bracket">[</span>38<span class="cite-bracket">]</span></a></sup> </td></tr> <tr> <td><a href="/wiki/Human_skin" title="Human skin">Human skin</a></td> <td>4.7<sup id="cite_ref-41" class="reference"><a href="#cite_note-41"><span class="cite-bracket">[</span>41<span class="cite-bracket">]</span></a></sup> </td></tr> <tr> <td>Granules of <a href="/wiki/Chromaffin_cell" title="Chromaffin cell">chromaffin cells</a></td> <td>5.5 </td></tr> <tr> <td><a href="/wiki/Urine" title="Urine">Urine</a></td> <td>6.0 </td></tr> <tr> <td><a href="/wiki/Breast_milk" title="Breast milk">Breast milk</a></td> <td>7.0–7.45<sup id="cite_ref-42" class="reference"><a href="#cite_note-42"><span class="cite-bracket">[</span>42<span class="cite-bracket">]</span></a></sup> </td></tr> <tr> <td><a href="/wiki/Cytosol" title="Cytosol">Cytosol</a></td> <td>7.2 </td></tr> <tr> <td><a href="/wiki/Blood" title="Blood">Blood</a> (natural pH)</td> <td>7.34–7.45<sup id="cite_ref-Boron2012_38-2" class="reference"><a href="#cite_note-Boron2012-38"><span class="cite-bracket">[</span>38<span class="cite-bracket">]</span></a></sup> </td></tr> <tr> <td><a href="/wiki/Cerebrospinal_fluid" title="Cerebrospinal fluid">Cerebrospinal fluid</a> (CSF)</td> <td>7.5 </td></tr> <tr> <td><a href="/wiki/Mitochondrial_matrix" title="Mitochondrial matrix">Mitochondrial matrix</a></td> <td>7.5 </td></tr> <tr> <td><a href="/wiki/Pancreas" title="Pancreas">Pancreas</a> secretions</td> <td>8.1 </td></tr></tbody></table></dd></dl> <p>In living organisms, the pH of various <a href="/wiki/Body_fluid" title="Body fluid">Body fluids</a>, cellular compartments, and organs is tightly regulated to maintain a state of acid-base balance known as <a href="/wiki/Acid%E2%80%93base_homeostasis" title="Acid–base homeostasis">acid–base homeostasis</a>. <a href="/wiki/Acidosis" title="Acidosis">Acidosis</a>, defined by blood pH below 7.35, is the most common disorder of acid–base homeostasis and occurs when there is an excess of acid in the body. In contrast, <a href="/wiki/Alkalosis" title="Alkalosis">alkalosis</a> is characterized by excessively high blood pH. </p><p>Blood pH is usually slightly basic, with a pH of 7.365, referred to as physiological pH in biology and medicine. <a href="/wiki/Dental_plaque" title="Dental plaque">Plaque</a> formation in teeth can create a local acidic environment that results in <a href="/wiki/Tooth_decay" title="Tooth decay">tooth decay</a> through demineralization. <a href="/wiki/Enzyme" title="Enzyme">Enzymes</a> and other <a href="/wiki/Protein" title="Protein">Proteins</a> have an optimal pH range for function and can become inactivated or <a href="/wiki/Denaturation_(biochemistry)" title="Denaturation (biochemistry)">denatured</a> outside this range. </p> <div class="mw-heading mw-heading2"><h2 id="pH_calculations">pH calculations</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=PH&action=edit&section=18" title="Edit section: pH calculations"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>When calculating the pH of a solution containing acids and/or bases, a <a href="/wiki/Determination_of_equilibrium_constants#Speciation_calculations" title="Determination of equilibrium constants">chemical speciation calculation</a> is used to determine the concentration of all chemical species present in the solution. The complexity of the procedure depends on the nature of the solution. Strong acids and bases are compounds that are almost completely dissociated in water, which simplifies the calculation. However, for weak acids, a <a href="/wiki/Quadratic_equation" title="Quadratic equation">quadratic equation</a> must be solved, and for weak bases, a cubic equation is required. In general, a set of <a href="/wiki/Non-linear" class="mw-redirect" title="Non-linear">non-linear</a> <a href="/wiki/Simultaneous_equation" class="mw-redirect" title="Simultaneous equation">simultaneous equations</a> must be solved. </p><p>Water itself is a weak acid and a weak base, so its dissociation must be taken into account at high pH and low solute concentration (see <i><a href="/wiki/Amphoterism" title="Amphoterism">Amphoterism</a></i>). It <a href="/wiki/Self-ionization_of_water" title="Self-ionization of water">dissociates</a> according to the equilibrium </p> <dl><dd><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">2 H<sub class="template-chem2-sub">2</sub>O ⇌ H<sub class="template-chem2-sub">3</sub>O<sup class="template-chem2-sup">+</sup> (aq) + OH<sup class="template-chem2-sup">−</sup> (aq)</span></dd></dl> <p>with a <a href="/wiki/Acid_dissociation_constant" title="Acid dissociation constant">dissociation constant</a>, <span class="texhtml"><i>K</i><sub>w</sub></span> defined as </p> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle K_{\text{w}}={\ce {[H+][OH^{-}]}}}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <msub> <mi>K</mi> <mrow class="MJX-TeXAtom-ORD"> <mtext>w</mtext> </mrow> </msub> <mo>=</mo> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-ORD"> <mo stretchy="false">[</mo> <msup> <mtext>H</mtext> <mrow class="MJX-TeXAtom-ORD"> <mo>+</mo> </mrow> </msup> <mo stretchy="false">]</mo> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mo stretchy="false">[</mo> <msup> <mtext>OH</mtext> <mrow class="MJX-TeXAtom-ORD"> <mo>−</mo> </mrow> </msup> <mo stretchy="false">]</mo> </mrow> </mrow> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle K_{\text{w}}={\ce {[H+][OH^{-}]}}}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/b3cd9093573ebd180683045ee786fc8c3fd2260c" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:17.394ex; height:3.009ex;" alt="{\displaystyle K_{\text{w}}={\ce {[H+][OH^{-}]}}}"></span></dd></dl> <p>where [H<sup>+</sup>] stands for the concentration of the aqueous <a href="/wiki/Hydronium_ion" class="mw-redirect" title="Hydronium ion">hydronium ion</a> and [OH<sup>−</sup>] represents the concentration of the <a href="/wiki/Hydroxide_ion" class="mw-redirect" title="Hydroxide ion">hydroxide ion</a>. This equilibrium needs to be taken into account at high pH and when the solute concentration is extremely low. </p> <div class="mw-heading mw-heading3"><h3 id="Strong_acids_and_bases">Strong acids and bases</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=PH&action=edit&section=19" title="Edit section: Strong acids and bases"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p><a href="/wiki/Strong_acid" class="mw-redirect" title="Strong acid">Strong acids</a> and <a href="/wiki/Strong_base" class="mw-redirect" title="Strong base">bases</a> are compounds that are essentially fully dissociated in water. This means that in an acidic solution, the concentration of hydrogen ions (H+) can be considered equal to the concentration of the acid. Similarly, in a basic solution, the concentration of hydroxide ions (OH-) can be considered equal to the concentration of the base. The pH of a solution is defined as the negative logarithm of the concentration of H<sup>+</sup>, and the pOH is defined as the negative logarithm of the concentration of OH<sup>−</sup>. For example, the pH of a 0.01 in <a href="/wiki/Mole_(unit)" title="Mole (unit)">moles</a> per litreM solution of hydrochloric acid (HCl) is equal to 2 (pH = −log<sub>10</sub>(0.01)), while the pOH of a 0.01 M solution of sodium hydroxide (NaOH) is equal to 2 (pOH = −log<sub>10</sub>(0.01)), which corresponds to a pH of about 12. </p><p>However, self-ionization of water must also be considered when concentrations of a strong acid or base is very low or high. For instance, a <span class="nowrap"><span data-sort-value="6992500000000000000♠"></span>5<span style="margin-left:0.25em;margin-right:0.15em;">×</span>10<sup>−8</sup> M</span> solution of HCl would be expected to have a pH of 7.3 based on the above procedure, which is incorrect as it is acidic and should have a pH of less than 7. In such cases, the system can be treated as a mixture of the acid or base and water, which is an <a href="/wiki/Amphoteric" class="mw-redirect" title="Amphoteric">amphoteric</a> substance. By accounting for the self-ionization of water, the true pH of the solution can be calculated. For example, a <span class="nowrap"><span data-sort-value="6992500000000000000♠"></span>5<span style="margin-left:0.25em;margin-right:0.15em;">×</span>10<sup>−8</sup> M</span> solution of HCl would have a pH of 6.89 when treated as a mixture of HCl and water. The self-ionization equilibrium of solutions of sodium hydroxide at higher concentrations must also be considered.<sup id="cite_ref-43" class="reference"><a href="#cite_note-43"><span class="cite-bracket">[</span>43<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Weak_acids_and_bases">Weak acids and bases</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=PH&action=edit&section=20" title="Edit section: Weak acids and bases"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>A <a href="/wiki/Weak_acid" class="mw-redirect" title="Weak acid">weak acid</a> or the conjugate acid of a weak base can be treated using the same formalism. </p> <ul><li>Acid HA: <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">HA ⇌ H<sup class="template-chem2-sup">+</sup> + A<sup class="template-chem2-sup">−</sup></span></li> <li>Base A: <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">HA<sup class="template-chem2-sup">+</sup> ⇌ H<sup class="template-chem2-sup">+</sup> + A</span></li></ul> <p>First, an acid dissociation constant is defined as follows. Electrical charges are omitted from subsequent equations for the sake of generality </p> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle K_{a}={\frac {{\ce {[H] [A]}}}{{\ce {[HA]}}}}}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <msub> <mi>K</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>a</mi> </mrow> </msub> <mo>=</mo> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-ORD"> <mo stretchy="false">[</mo> <mtext>H</mtext> <mo stretchy="false">]</mo> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mo stretchy="false">[</mo> <mtext>A</mtext> <mo stretchy="false">]</mo> </mrow> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-ORD"> <mo stretchy="false">[</mo> <mtext>HA</mtext> <mo stretchy="false">]</mo> </mrow> </mrow> </mfrac> </mrow> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle K_{a}={\frac {{\ce {[H] [A]}}}{{\ce {[HA]}}}}}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/f29a403e204523dcc5d4345e9da4125d6bccc8e0" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -2.671ex; width:13.083ex; height:6.509ex;" alt="{\displaystyle K_{a}={\frac {{\ce {[H] [A]}}}{{\ce {[HA]}}}}}"></span></dd></dl> <p>and its value is assumed to have been determined by experiment. This being so, there are three unknown concentrations, [HA], [H<sup>+</sup>] and [A<sup>−</sup>] to determine by calculation. Two additional equations are needed. One way to provide them is to apply the law of <a href="/wiki/Mass_conservation" class="mw-redirect" title="Mass conservation">mass conservation</a> in terms of the two "reagents" H and A. </p> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle C_{{\ce {A}}}={\ce {[A]}}+{\ce {[HA]}}}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <msub> <mi>C</mi> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-ORD"> <mtext>A</mtext> </mrow> </mrow> </msub> <mo>=</mo> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-ORD"> <mo stretchy="false">[</mo> <mtext>A</mtext> <mo stretchy="false">]</mo> </mrow> </mrow> <mo>+</mo> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-ORD"> <mo stretchy="false">[</mo> <mtext>HA</mtext> <mo stretchy="false">]</mo> </mrow> </mrow> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle C_{{\ce {A}}}={\ce {[A]}}+{\ce {[HA]}}}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/9ebde93fda69a21943e8842a9a32da905b2f645e" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:16.882ex; height:2.843ex;" alt="{\displaystyle C_{{\ce {A}}}={\ce {[A]}}+{\ce {[HA]}}}"></span></dd> <dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle C_{{\ce {H}}}={\ce {[H]}}+{\ce {[HA]}}}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <msub> <mi>C</mi> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-ORD"> <mtext>H</mtext> </mrow> </mrow> </msub> <mo>=</mo> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-ORD"> <mo stretchy="false">[</mo> <mtext>H</mtext> <mo stretchy="false">]</mo> </mrow> </mrow> <mo>+</mo> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-ORD"> <mo stretchy="false">[</mo> <mtext>HA</mtext> <mo stretchy="false">]</mo> </mrow> </mrow> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle C_{{\ce {H}}}={\ce {[H]}}+{\ce {[HA]}}}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/920b90697a63b1c14c8302e733fc525ba0d9585b" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:16.882ex; height:2.843ex;" alt="{\displaystyle C_{{\ce {H}}}={\ce {[H]}}+{\ce {[HA]}}}"></span></dd></dl> <p><i>C</i> stands for <a href="/wiki/Analytical_concentration" class="mw-redirect" title="Analytical concentration">analytical concentration</a>. In some texts, one mass balance equation is replaced by an equation of charge balance. This is satisfactory for simple cases like this one, but is more difficult to apply to more complicated cases as those below. Together with the equation defining <i>K</i><sub>a</sub>, there are now three equations in three unknowns. When an acid is dissolved in water <i>C</i><sub>A</sub> = <i>C</i><sub>H</sub> = <i>C</i><sub>a</sub>, the concentration of the acid, so [A] = [H]. After some further algebraic manipulation an equation in the hydrogen ion concentration may be obtained. </p> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle [{\ce {H}}]^{2}+K_{a}[{\ce {H}}]-K_{a}C_{a}=0}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mo stretchy="false">[</mo> <mrow class="MJX-TeXAtom-ORD"> <mtext>H</mtext> </mrow> <msup> <mo stretchy="false">]</mo> <mrow class="MJX-TeXAtom-ORD"> <mn>2</mn> </mrow> </msup> <mo>+</mo> <msub> <mi>K</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>a</mi> </mrow> </msub> <mo stretchy="false">[</mo> <mrow class="MJX-TeXAtom-ORD"> <mtext>H</mtext> </mrow> <mo stretchy="false">]</mo> <mo>−</mo> <msub> <mi>K</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>a</mi> </mrow> </msub> <msub> <mi>C</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>a</mi> </mrow> </msub> <mo>=</mo> <mn>0</mn> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle [{\ce {H}}]^{2}+K_{a}[{\ce {H}}]-K_{a}C_{a}=0}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/46348613cafd9be4dcf2b772575b5af47f080d54" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:25.983ex; height:3.176ex;" alt="{\displaystyle [{\ce {H}}]^{2}+K_{a}[{\ce {H}}]-K_{a}C_{a}=0}"></span></dd></dl> <p>Solution of this <a href="/wiki/Quadratic_equation" title="Quadratic equation">quadratic equation</a> gives the hydrogen ion concentration and hence p[H] or, more loosely, pH. This procedure is illustrated in an <a href="/wiki/ICE_table" class="mw-redirect" title="ICE table">ICE table</a> which can also be used to calculate the pH when some additional (strong) acid or alkaline has been added to the system, that is, when <i>C</i><sub>A</sub> ≠ <i>C</i><sub>H</sub>. </p><p>For example, what is the pH of a 0.01 M solution of <a href="/wiki/Benzoic_acid" title="Benzoic acid">benzoic acid</a>, p<i>K</i><sub>a</sub> = 4.19? </p> <ul><li>Step 1: <span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle K_{a}=10^{-4.19}=6.46\times 10^{-5}}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <msub> <mi>K</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>a</mi> </mrow> </msub> <mo>=</mo> <msup> <mn>10</mn> <mrow class="MJX-TeXAtom-ORD"> <mo>−</mo> <mn>4.19</mn> </mrow> </msup> <mo>=</mo> <mn>6.46</mn> <mo>×</mo> <msup> <mn>10</mn> <mrow class="MJX-TeXAtom-ORD"> <mo>−</mo> <mn>5</mn> </mrow> </msup> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle K_{a}=10^{-4.19}=6.46\times 10^{-5}}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/8ba5721f63f313ffed3e2d4f1c4c0470276b2445" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.671ex; width:27.663ex; height:3.009ex;" alt="{\displaystyle K_{a}=10^{-4.19}=6.46\times 10^{-5}}"></span></li> <li>Step 2: Set up the quadratic equation. <span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle [{\ce {H}}]^{2}+6.46\times 10^{-5}[{\ce {H}}]-6.46\times 10^{-7}=0}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mo stretchy="false">[</mo> <mrow class="MJX-TeXAtom-ORD"> <mtext>H</mtext> </mrow> <msup> <mo stretchy="false">]</mo> <mrow class="MJX-TeXAtom-ORD"> <mn>2</mn> </mrow> </msup> <mo>+</mo> <mn>6.46</mn> <mo>×</mo> <msup> <mn>10</mn> <mrow class="MJX-TeXAtom-ORD"> <mo>−</mo> <mn>5</mn> </mrow> </msup> <mo stretchy="false">[</mo> <mrow class="MJX-TeXAtom-ORD"> <mtext>H</mtext> </mrow> <mo stretchy="false">]</mo> <mo>−</mo> <mn>6.46</mn> <mo>×</mo> <msup> <mn>10</mn> <mrow class="MJX-TeXAtom-ORD"> <mo>−</mo> <mn>7</mn> </mrow> </msup> <mo>=</mo> <mn>0</mn> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle [{\ce {H}}]^{2}+6.46\times 10^{-5}[{\ce {H}}]-6.46\times 10^{-7}=0}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/3b00dbc68e7860d66750e413f778916b6b915cd9" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:40.334ex; height:3.176ex;" alt="{\displaystyle [{\ce {H}}]^{2}+6.46\times 10^{-5}[{\ce {H}}]-6.46\times 10^{-7}=0}"></span></li> <li>Step 3: Solve the quadratic equation. <span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle [{\ce {H+}}]=7.74\times 10^{-4};\quad \mathrm {pH} =3.11}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mo stretchy="false">[</mo> <mrow class="MJX-TeXAtom-ORD"> <msup> <mtext>H</mtext> <mrow class="MJX-TeXAtom-ORD"> <mo>+</mo> </mrow> </msup> </mrow> <mo stretchy="false">]</mo> <mo>=</mo> <mn>7.74</mn> <mo>×</mo> <msup> <mn>10</mn> <mrow class="MJX-TeXAtom-ORD"> <mo>−</mo> <mn>4</mn> </mrow> </msup> <mo>;</mo> <mspace width="1em" /> <mrow class="MJX-TeXAtom-ORD"> <mi mathvariant="normal">p</mi> <mi mathvariant="normal">H</mi> </mrow> <mo>=</mo> <mn>3.11</mn> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle [{\ce {H+}}]=7.74\times 10^{-4};\quad \mathrm {pH} =3.11}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/d23e6dd79b1f843749965771698d8a5403a236a4" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:32.903ex; height:3.176ex;" alt="{\displaystyle [{\ce {H+}}]=7.74\times 10^{-4};\quad \mathrm {pH} =3.11}"></span></li></ul> <p>For alkaline solutions, an additional term is added to the mass-balance equation for hydrogen. Since the addition of hydroxide reduces the hydrogen ion concentration, and the hydroxide ion concentration is constrained by the self-ionization equilibrium to be equal to <span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle {\frac {K_{w}}{{\ce {[H+]}}}}}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <msub> <mi>K</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>w</mi> </mrow> </msub> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-ORD"> <mo stretchy="false">[</mo> <msup> <mtext>H</mtext> <mrow class="MJX-TeXAtom-ORD"> <mo>+</mo> </mrow> </msup> <mo stretchy="false">]</mo> </mrow> </mrow> </mfrac> </mrow> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle {\frac {K_{w}}{{\ce {[H+]}}}}}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/671c1d10d6bce20ed4de57be093835a6aad5019f" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -2.838ex; width:5.384ex; height:6.176ex;" alt="{\displaystyle {\frac {K_{w}}{{\ce {[H+]}}}}}"></span>, the resulting equation is: </p> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle C_{\ce {H}}={\frac {[{\ce {H}}]+[{\ce {HA}}]-K_{w}}{\ce {[H]}}}}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <msub> <mi>C</mi> <mrow class="MJX-TeXAtom-ORD"> <mtext>H</mtext> </mrow> </msub> <mo>=</mo> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <mrow> <mo stretchy="false">[</mo> <mrow class="MJX-TeXAtom-ORD"> <mtext>H</mtext> </mrow> <mo stretchy="false">]</mo> <mo>+</mo> <mo stretchy="false">[</mo> <mrow class="MJX-TeXAtom-ORD"> <mtext>HA</mtext> </mrow> <mo stretchy="false">]</mo> <mo>−</mo> <msub> <mi>K</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>w</mi> </mrow> </msub> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mo stretchy="false">[</mo> <mtext>H</mtext> <mo stretchy="false">]</mo> </mrow> </mfrac> </mrow> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle C_{\ce {H}}={\frac {[{\ce {H}}]+[{\ce {HA}}]-K_{w}}{\ce {[H]}}}}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/e4eaeb404231cb0a9a118cd2972dc991b67adaab" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -2.671ex; width:23.941ex; height:6.509ex;" alt="{\displaystyle C_{\ce {H}}={\frac {[{\ce {H}}]+[{\ce {HA}}]-K_{w}}{\ce {[H]}}}}"></span></dd></dl> <div class="mw-heading mw-heading3"><h3 id="General_method">General method</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=PH&action=edit&section=21" title="Edit section: General method"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Some systems, such as with <a href="/wiki/Polyprotic" class="mw-redirect" title="Polyprotic">polyprotic</a> acids, are amenable to spreadsheet calculations.<sup id="cite_ref-44" class="reference"><a href="#cite_note-44"><span class="cite-bracket">[</span>44<span class="cite-bracket">]</span></a></sup> With three or more reagents or when many complexes are formed with general formulae such as A<sub>p</sub>B<sub>q</sub>H<sub>r</sub>, the following general method can be used to calculate the pH of a solution. For example, with three reagents, each equilibrium is characterized by an equilibrium constant, <i>β</i>. </p> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle [{\ce {A}}_{p}{\ce {B}}_{q}{\ce {H}}_{r}]=\beta _{pqr}[{\ce {A}}]^{p}[{\ce {B}}]^{q}[{\ce {H}}]^{r}}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mo stretchy="false">[</mo> <msub> <mrow class="MJX-TeXAtom-ORD"> <mtext>A</mtext> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mi>p</mi> </mrow> </msub> <msub> <mrow class="MJX-TeXAtom-ORD"> <mtext>B</mtext> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mi>q</mi> </mrow> </msub> <msub> <mrow class="MJX-TeXAtom-ORD"> <mtext>H</mtext> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mi>r</mi> </mrow> </msub> <mo stretchy="false">]</mo> <mo>=</mo> <msub> <mi>β</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>p</mi> <mi>q</mi> <mi>r</mi> </mrow> </msub> <mo stretchy="false">[</mo> <mrow class="MJX-TeXAtom-ORD"> <mtext>A</mtext> </mrow> <msup> <mo stretchy="false">]</mo> <mrow class="MJX-TeXAtom-ORD"> <mi>p</mi> </mrow> </msup> <mo stretchy="false">[</mo> <mrow class="MJX-TeXAtom-ORD"> <mtext>B</mtext> </mrow> <msup> <mo stretchy="false">]</mo> <mrow class="MJX-TeXAtom-ORD"> <mi>q</mi> </mrow> </msup> <mo stretchy="false">[</mo> <mrow class="MJX-TeXAtom-ORD"> <mtext>H</mtext> </mrow> <msup> <mo stretchy="false">]</mo> <mrow class="MJX-TeXAtom-ORD"> <mi>r</mi> </mrow> </msup> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle [{\ce {A}}_{p}{\ce {B}}_{q}{\ce {H}}_{r}]=\beta _{pqr}[{\ce {A}}]^{p}[{\ce {B}}]^{q}[{\ce {H}}]^{r}}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/0116cc100cbe49e89c845e94bfb7cfa9d41efdf4" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -1.005ex; width:28.452ex; height:3.009ex;" alt="{\displaystyle [{\ce {A}}_{p}{\ce {B}}_{q}{\ce {H}}_{r}]=\beta _{pqr}[{\ce {A}}]^{p}[{\ce {B}}]^{q}[{\ce {H}}]^{r}}"></span></dd></dl> <p>Next, write down the mass-balance equations for each reagent: </p> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle {\begin{aligned}C_{\ce {A}}&=[{\ce {A}}]+\Sigma p\beta _{pqr}[{\ce {A}}]^{p}[{\ce {B}}]^{q}[{\ce {H}}]^{r}\\C_{\ce {B}}&=[{\ce {B}}]+\Sigma q\beta _{pqr}[{\ce {A}}]^{p}[{\ce {B}}]^{q}[{\ce {H}}]^{r}\\C_{\ce {H}}&=[{\ce {H}}]+\Sigma r\beta _{pqr}[{\ce {A}}]^{p}[{\ce {B}}]^{q}[{\ce {H}}]^{r}-K_{w}[{\ce {H}}]^{-1}\end{aligned}}}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mrow class="MJX-TeXAtom-ORD"> <mtable columnalign="right left right left right left right left right left right left" rowspacing="3pt" columnspacing="0em 2em 0em 2em 0em 2em 0em 2em 0em 2em 0em" displaystyle="true"> <mtr> <mtd> <msub> <mi>C</mi> <mrow class="MJX-TeXAtom-ORD"> <mtext>A</mtext> </mrow> </msub> </mtd> <mtd> <mi></mi> <mo>=</mo> <mo stretchy="false">[</mo> <mrow class="MJX-TeXAtom-ORD"> <mtext>A</mtext> </mrow> <mo stretchy="false">]</mo> <mo>+</mo> <mi mathvariant="normal">Σ</mi> <mi>p</mi> <msub> <mi>β</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>p</mi> <mi>q</mi> <mi>r</mi> </mrow> </msub> <mo stretchy="false">[</mo> <mrow class="MJX-TeXAtom-ORD"> <mtext>A</mtext> </mrow> <msup> <mo stretchy="false">]</mo> <mrow class="MJX-TeXAtom-ORD"> <mi>p</mi> </mrow> </msup> <mo stretchy="false">[</mo> <mrow class="MJX-TeXAtom-ORD"> <mtext>B</mtext> </mrow> <msup> <mo stretchy="false">]</mo> <mrow class="MJX-TeXAtom-ORD"> <mi>q</mi> </mrow> </msup> <mo stretchy="false">[</mo> <mrow class="MJX-TeXAtom-ORD"> <mtext>H</mtext> </mrow> <msup> <mo stretchy="false">]</mo> <mrow class="MJX-TeXAtom-ORD"> <mi>r</mi> </mrow> </msup> </mtd> </mtr> <mtr> <mtd> <msub> <mi>C</mi> <mrow class="MJX-TeXAtom-ORD"> <mtext>B</mtext> </mrow> </msub> </mtd> <mtd> <mi></mi> <mo>=</mo> <mo stretchy="false">[</mo> <mrow class="MJX-TeXAtom-ORD"> <mtext>B</mtext> </mrow> <mo stretchy="false">]</mo> <mo>+</mo> <mi mathvariant="normal">Σ</mi> <mi>q</mi> <msub> <mi>β</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>p</mi> <mi>q</mi> <mi>r</mi> </mrow> </msub> <mo stretchy="false">[</mo> <mrow class="MJX-TeXAtom-ORD"> <mtext>A</mtext> </mrow> <msup> <mo stretchy="false">]</mo> <mrow class="MJX-TeXAtom-ORD"> <mi>p</mi> </mrow> </msup> <mo stretchy="false">[</mo> <mrow class="MJX-TeXAtom-ORD"> <mtext>B</mtext> </mrow> <msup> <mo stretchy="false">]</mo> <mrow class="MJX-TeXAtom-ORD"> <mi>q</mi> </mrow> </msup> <mo stretchy="false">[</mo> <mrow class="MJX-TeXAtom-ORD"> <mtext>H</mtext> </mrow> <msup> <mo stretchy="false">]</mo> <mrow class="MJX-TeXAtom-ORD"> <mi>r</mi> </mrow> </msup> </mtd> </mtr> <mtr> <mtd> <msub> <mi>C</mi> <mrow class="MJX-TeXAtom-ORD"> <mtext>H</mtext> </mrow> </msub> </mtd> <mtd> <mi></mi> <mo>=</mo> <mo stretchy="false">[</mo> <mrow class="MJX-TeXAtom-ORD"> <mtext>H</mtext> </mrow> <mo stretchy="false">]</mo> <mo>+</mo> <mi mathvariant="normal">Σ</mi> <mi>r</mi> <msub> <mi>β</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>p</mi> <mi>q</mi> <mi>r</mi> </mrow> </msub> <mo stretchy="false">[</mo> <mrow class="MJX-TeXAtom-ORD"> <mtext>A</mtext> </mrow> <msup> <mo stretchy="false">]</mo> <mrow class="MJX-TeXAtom-ORD"> <mi>p</mi> </mrow> </msup> <mo stretchy="false">[</mo> <mrow class="MJX-TeXAtom-ORD"> <mtext>B</mtext> </mrow> <msup> <mo stretchy="false">]</mo> <mrow class="MJX-TeXAtom-ORD"> <mi>q</mi> </mrow> </msup> <mo stretchy="false">[</mo> <mrow class="MJX-TeXAtom-ORD"> <mtext>H</mtext> </mrow> <msup> <mo stretchy="false">]</mo> <mrow class="MJX-TeXAtom-ORD"> <mi>r</mi> </mrow> </msup> <mo>−</mo> <msub> <mi>K</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>w</mi> </mrow> </msub> <mo stretchy="false">[</mo> <mrow class="MJX-TeXAtom-ORD"> <mtext>H</mtext> </mrow> <msup> <mo stretchy="false">]</mo> <mrow class="MJX-TeXAtom-ORD"> <mo>−</mo> <mn>1</mn> </mrow> </msup> </mtd> </mtr> </mtable> </mrow> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle {\begin{aligned}C_{\ce {A}}&=[{\ce {A}}]+\Sigma p\beta _{pqr}[{\ce {A}}]^{p}[{\ce {B}}]^{q}[{\ce {H}}]^{r}\\C_{\ce {B}}&=[{\ce {B}}]+\Sigma q\beta _{pqr}[{\ce {A}}]^{p}[{\ce {B}}]^{q}[{\ce {H}}]^{r}\\C_{\ce {H}}&=[{\ce {H}}]+\Sigma r\beta _{pqr}[{\ce {A}}]^{p}[{\ce {B}}]^{q}[{\ce {H}}]^{r}-K_{w}[{\ce {H}}]^{-1}\end{aligned}}}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/3d204f0d1baca5254f67602e86ba0091a004b673" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -4.338ex; width:43.079ex; height:9.676ex;" alt="{\displaystyle {\begin{aligned}C_{\ce {A}}&=[{\ce {A}}]+\Sigma p\beta _{pqr}[{\ce {A}}]^{p}[{\ce {B}}]^{q}[{\ce {H}}]^{r}\\C_{\ce {B}}&=[{\ce {B}}]+\Sigma q\beta _{pqr}[{\ce {A}}]^{p}[{\ce {B}}]^{q}[{\ce {H}}]^{r}\\C_{\ce {H}}&=[{\ce {H}}]+\Sigma r\beta _{pqr}[{\ce {A}}]^{p}[{\ce {B}}]^{q}[{\ce {H}}]^{r}-K_{w}[{\ce {H}}]^{-1}\end{aligned}}}"></span></dd></dl> <p>There are no approximations involved in these equations, except that each stability constant is defined as a quotient of concentrations, not activities. Much more complicated expressions are required if activities are to be used. </p><p>There are three <a href="/wiki/Simultaneous_equation" class="mw-redirect" title="Simultaneous equation">simultaneous equations</a> in the three unknowns, [A], [B] and [H]. Because the equations are non-linear and their concentrations may range over many powers of 10, the solution of these equations is not straightforward. However, many computer programs are available which can be used to perform these calculations. There may be more than three reagents. The calculation of hydrogen ion concentrations, using this approach, is a key element in the <a href="/wiki/Determination_of_equilibrium_constants" title="Determination of equilibrium constants">determination of equilibrium constants</a> by <a href="/wiki/Potentiometric_titration" title="Potentiometric titration">potentiometric titration</a>. </p> <div class="mw-heading mw-heading2"><h2 id="See_also">See also</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=PH&action=edit&section=22" title="Edit section: See also"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li><a href="/wiki/PH_indicator" title="PH indicator">pH indicator</a></li> <li><a href="/wiki/Arterial_blood_gas" class="mw-redirect" title="Arterial blood gas">Arterial blood gas</a></li> <li><a href="/wiki/Chemical_equilibrium" title="Chemical equilibrium">Chemical equilibrium</a></li> <li><a href="/wiki/Acid_dissociation_constant" title="Acid dissociation constant">p<i>K</i><sub>a</sub></a></li></ul> <div class="mw-heading mw-heading2"><h2 id="References">References</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=PH&action=edit&section=23" title="Edit section: References"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <style data-mw-deduplicate="TemplateStyles:r1239543626">.mw-parser-output .reflist{margin-bottom:0.5em;list-style-type:decimal}@media screen{.mw-parser-output .reflist{font-size:90%}}.mw-parser-output .reflist .references{font-size:100%;margin-bottom:0;list-style-type:inherit}.mw-parser-output .reflist-columns-2{column-width:30em}.mw-parser-output .reflist-columns-3{column-width:25em}.mw-parser-output .reflist-columns{margin-top:0.3em}.mw-parser-output .reflist-columns ol{margin-top:0}.mw-parser-output .reflist-columns li{page-break-inside:avoid;break-inside:avoid-column}.mw-parser-output .reflist-upper-alpha{list-style-type:upper-alpha}.mw-parser-output .reflist-upper-roman{list-style-type:upper-roman}.mw-parser-output .reflist-lower-alpha{list-style-type:lower-alpha}.mw-parser-output .reflist-lower-greek{list-style-type:lower-greek}.mw-parser-output .reflist-lower-roman{list-style-type:lower-roman}</style><div class="reflist"> <div class="mw-references-wrap mw-references-columns"><ol class="references"> <li id="cite_note-1"><span class="mw-cite-backlink"><b><a href="#cite_ref-1">^</a></b></span> <span class="reference-text"><style data-mw-deduplicate="TemplateStyles:r1238218222">.mw-parser-output cite.citation{font-style:inherit;word-wrap:break-word}.mw-parser-output .citation q{quotes:"\"""\"""'""'"}.mw-parser-output .citation:target{background-color:rgba(0,127,255,0.133)}.mw-parser-output .id-lock-free.id-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/6/65/Lock-green.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-limited.id-lock-limited a,.mw-parser-output .id-lock-registration.id-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/d/d6/Lock-gray-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-subscription.id-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/a/aa/Lock-red-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .cs1-ws-icon a{background:url("//upload.wikimedia.org/wikipedia/commons/4/4c/Wikisource-logo.svg")right 0.1em center/12px no-repeat}body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-free a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-limited a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-registration a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-subscription a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .cs1-ws-icon a{background-size:contain;padding:0 1em 0 0}.mw-parser-output .cs1-code{color:inherit;background:inherit;border:none;padding:inherit}.mw-parser-output .cs1-hidden-error{display:none;color:var(--color-error,#d33)}.mw-parser-output .cs1-visible-error{color:var(--color-error,#d33)}.mw-parser-output .cs1-maint{display:none;color:#085;margin-left:0.3em}.mw-parser-output .cs1-kern-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right{padding-right:0.2em}.mw-parser-output .citation .mw-selflink{font-weight:inherit}@media screen{.mw-parser-output .cs1-format{font-size:95%}html.skin-theme-clientpref-night .mw-parser-output .cs1-maint{color:#18911f}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .cs1-maint{color:#18911f}}</style><cite id="CITEREFJensen2004" class="citation journal cs1"><a href="/wiki/William_B._Jensen" title="William B. Jensen">Jensen, William B.</a> (2004). <a rel="nofollow" class="external text" href="http://www.che.uc.edu/jensen/W.%20B.%20Jensen/Reprints/102.%20pH.pdf">"The Symbol for pH"</a> <span class="cs1-format">(PDF)</span>. <i>Journal of Chemical Education</i>. <b>81</b> (1): 21. <a href="/wiki/Bibcode_(identifier)" class="mw-redirect" title="Bibcode (identifier)">Bibcode</a>:<a rel="nofollow" class="external text" href="https://ui.adsabs.harvard.edu/abs/2004JChEd..81...21J">2004JChEd..81...21J</a>. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1021%2Fed081p21">10.1021/ed081p21</a>. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20191214110759/http://www.che.uc.edu/jensen/w.%20b.%20jensen/reprints/102.%20ph.pdf">Archived</a> <span class="cs1-format">(PDF)</span> from the original on 14 December 2019<span class="reference-accessdate">. Retrieved <span class="nowrap">15 July</span> 2020</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Journal+of+Chemical+Education&rft.atitle=The+Symbol+for+pH&rft.volume=81&rft.issue=1&rft.pages=21&rft.date=2004&rft_id=info%3Adoi%2F10.1021%2Fed081p21&rft_id=info%3Abibcode%2F2004JChEd..81...21J&rft.aulast=Jensen&rft.aufirst=William+B.&rft_id=http%3A%2F%2Fwww.che.uc.edu%2Fjensen%2FW.%2520B.%2520Jensen%2FReprints%2F102.%2520pH.pdf&rfr_id=info%3Asid%2Fen.wikipedia.org%3APH" class="Z3988"></span></span> </li> <li id="cite_note-2"><span class="mw-cite-backlink"><b><a href="#cite_ref-2">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFLim2006" class="citation journal cs1">Lim, Kieran F. (2006). 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(13 January 2012). <a rel="nofollow" class="external text" href="https://books.google.com/books?id=54mxMgO5H_YC&dq=pH%20in%20living%20systems&pg=PA652"><i>Medical Physiology: A Cellular And Molecular Approach</i></a> (2nd ed.). <a href="/wiki/Elsevier_Health_Sciences" class="mw-redirect" title="Elsevier Health Sciences">Elsevier Health Sciences</a>, Saunders. pp. <span class="nowrap">652–</span>671. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/9781455711819" title="Special:BookSources/9781455711819"><bdi>9781455711819</bdi></a>. <a href="/wiki/OCLC_(identifier)" class="mw-redirect" title="OCLC (identifier)">OCLC</a> <a rel="nofollow" class="external text" href="https://search.worldcat.org/oclc/1017876653">1017876653</a>. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20220508051939/https://www.google.co.in/books/edition/_/54mxMgO5H_YC?hl=en&gbpv=1&dq=pH+in+living+systems&pg=PA652">Archived</a> from the original on 8 May 2022<span class="reference-accessdate">. Retrieved <span class="nowrap">8 May</span> 2022</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Medical+Physiology%3A+A+Cellular+And+Molecular+Approach&rft.pages=%3Cspan+class%3D%22nowrap%22%3E652-%3C%2Fspan%3E671&rft.edition=2nd&rft.pub=Elsevier+Health+Sciences%2C+Saunders&rft.date=2012-01-13&rft_id=info%3Aoclcnum%2F1017876653&rft.isbn=9781455711819&rft.aulast=Boron&rft.aufirst=Walter+F.&rft.au=Boulpaep%2C+Emile+L.&rft_id=https%3A%2F%2Fbooks.google.com%2Fbooks%3Fid%3D54mxMgO5H_YC%26dq%3DpH%2520in%2520living%2520systems%26pg%3DPA652&rfr_id=info%3Asid%2Fen.wikipedia.org%3APH" class="Z3988"></span></span> </li> <li id="cite_note-39"><span class="mw-cite-backlink"><b><a href="#cite_ref-39">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation news cs1"><a rel="nofollow" class="external text" href="https://www.ucsfhealth.org/medical-tests/stomach-acid-test">"Stomach acid test"</a>. University of California San Francisco<span class="reference-accessdate">. Retrieved <span class="nowrap">21 February</span> 2024</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.atitle=Stomach+acid+test&rft_id=https%3A%2F%2Fwww.ucsfhealth.org%2Fmedical-tests%2Fstomach-acid-test&rfr_id=info%3Asid%2Fen.wikipedia.org%3APH" class="Z3988"></span></span> </li> <li id="cite_note-40"><span class="mw-cite-backlink"><b><a href="#cite_ref-40">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFMariebMitchell2011" class="citation book cs1">Marieb, Elaine N.; Mitchell, Susan J. (30 June 2011). <a rel="nofollow" class="external text" href="https://books.google.com/books?id=BxDfnQEACAAJ"><i>Human anatomy & physiology</i></a>. San Francisco: <a href="/wiki/Benjamin_Cummings" title="Benjamin Cummings">Benjamin Cummings</a>. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/9780321735287" title="Special:BookSources/9780321735287"><bdi>9780321735287</bdi></a>. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20220508051937/https://www.google.co.in/books/edition/_/BxDfnQEACAAJ?hl=en">Archived</a> from the original on 8 May 2022<span class="reference-accessdate">. Retrieved <span class="nowrap">8 May</span> 2022</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Human+anatomy+%26+physiology&rft.place=San+Francisco&rft.pub=Benjamin+Cummings&rft.date=2011-06-30&rft.isbn=9780321735287&rft.aulast=Marieb&rft.aufirst=Elaine+N.&rft.au=Mitchell%2C+Susan+J.&rft_id=https%3A%2F%2Fbooks.google.com%2Fbooks%3Fid%3DBxDfnQEACAAJ&rfr_id=info%3Asid%2Fen.wikipedia.org%3APH" class="Z3988"></span></span> </li> <li id="cite_note-41"><span class="mw-cite-backlink"><b><a href="#cite_ref-41">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFLambersPiessensBloemPronk2006" class="citation journal cs1">Lambers, H.; Piessens, S.; Bloem, A.; Pronk, H.; Finkel, P. (1 October 2006). <a rel="nofollow" class="external text" href="https://onlinelibrary.wiley.com/doi/10.1111/j.1467-2494.2006.00344.x">"Natural skin surface pH is on average below 5, which is beneficial for its resident flora"</a>. <i>International Journal of Cosmetic Science</i>. <b>28</b> (5): <span class="nowrap">359–</span>370. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1111%2Fj.1467-2494.2006.00344.x">10.1111/j.1467-2494.2006.00344.x</a>. <a href="/wiki/ISSN_(identifier)" class="mw-redirect" title="ISSN (identifier)">ISSN</a> <a rel="nofollow" class="external text" href="https://search.worldcat.org/issn/1468-2494">1468-2494</a>. <a href="/wiki/PMID_(identifier)" class="mw-redirect" title="PMID (identifier)">PMID</a> <a rel="nofollow" class="external text" href="https://pubmed.ncbi.nlm.nih.gov/18489300">18489300</a>. <a href="/wiki/S2CID_(identifier)" class="mw-redirect" title="S2CID (identifier)">S2CID</a> <a rel="nofollow" class="external text" href="https://api.semanticscholar.org/CorpusID:25191984">25191984</a>. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20220321033318/https://onlinelibrary.wiley.com/doi/10.1111/j.1467-2494.2006.00344.x">Archived</a> from the original on 21 March 2022<span class="reference-accessdate">. Retrieved <span class="nowrap">8 May</span> 2022</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=International+Journal+of+Cosmetic+Science&rft.atitle=Natural+skin+surface+pH+is+on+average+below+5%2C+which+is+beneficial+for+its+resident+flora&rft.volume=28&rft.issue=5&rft.pages=%3Cspan+class%3D%22nowrap%22%3E359-%3C%2Fspan%3E370&rft.date=2006-10-01&rft.issn=1468-2494&rft_id=https%3A%2F%2Fapi.semanticscholar.org%2FCorpusID%3A25191984%23id-name%3DS2CID&rft_id=info%3Apmid%2F18489300&rft_id=info%3Adoi%2F10.1111%2Fj.1467-2494.2006.00344.x&rft.aulast=Lambers&rft.aufirst=H.&rft.au=Piessens%2C+S.&rft.au=Bloem%2C+A.&rft.au=Pronk%2C+H.&rft.au=Finkel%2C+P.&rft_id=https%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1111%2Fj.1467-2494.2006.00344.x&rfr_id=info%3Asid%2Fen.wikipedia.org%3APH" class="Z3988"></span></span> </li> <li id="cite_note-42"><span class="mw-cite-backlink"><b><a href="#cite_ref-42">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFMorriss_JrBrewerSpedaleRiddle1986" class="citation journal cs1">Morriss Jr, F. H.; Brewer, E. D.; Spedale, S. B.; Riddle, L.; Temple, D. M.; Caprioli, R. M.; West, M. S. (1986). <a rel="nofollow" class="external text" href="https://pubmed.ncbi.nlm.nih.gov/3748680/#:~:text=Thereafter%2C%20the%20pH%20of%20milk,with%20the%20concentration%20of%20lactose">"Relationship of human milk pH during course of lactation to concentrations of citrate and fatty acids"</a>. <i>Pediatrics</i>. <b>78</b> (3): <span class="nowrap">458–</span>464. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1542%2Fpeds.78.3.458">10.1542/peds.78.3.458</a>. <a href="/wiki/PMID_(identifier)" class="mw-redirect" title="PMID (identifier)">PMID</a> <a rel="nofollow" class="external text" href="https://pubmed.ncbi.nlm.nih.gov/3748680">3748680</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Pediatrics&rft.atitle=Relationship+of+human+milk+pH+during+course+of+lactation+to+concentrations+of+citrate+and+fatty+acids&rft.volume=78&rft.issue=3&rft.pages=%3Cspan+class%3D%22nowrap%22%3E458-%3C%2Fspan%3E464&rft.date=1986&rft_id=info%3Adoi%2F10.1542%2Fpeds.78.3.458&rft_id=info%3Apmid%2F3748680&rft.aulast=Morriss+Jr&rft.aufirst=F.+H.&rft.au=Brewer%2C+E.+D.&rft.au=Spedale%2C+S.+B.&rft.au=Riddle%2C+L.&rft.au=Temple%2C+D.+M.&rft.au=Caprioli%2C+R.+M.&rft.au=West%2C+M.+S.&rft_id=https%3A%2F%2Fpubmed.ncbi.nlm.nih.gov%2F3748680%2F%23%3A~%3Atext%3DThereafter%252C%2520the%2520pH%2520of%2520milk%2Cwith%2520the%2520concentration%2520of%2520lactose&rfr_id=info%3Asid%2Fen.wikipedia.org%3APH" class="Z3988"></span></span> </li> <li id="cite_note-43"><span class="mw-cite-backlink"><b><a href="#cite_ref-43">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFMaloney" class="citation web cs1">Maloney, Chris. <a rel="nofollow" class="external text" href="http://sinophibe.blogspot.com/2011/03/ph-calculation-of-very-small.html">"pH calculation of a very small concentration of a strong acid"</a>. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20110708062942/http://sinophibe.blogspot.com/2011/03/ph-calculation-of-very-small.html">Archived</a> from the original on 8 July 2011<span class="reference-accessdate">. Retrieved <span class="nowrap">13 March</span> 2011</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=pH+calculation+of+a+very+small+concentration+of+a+strong+acid.&rft.aulast=Maloney&rft.aufirst=Chris&rft_id=http%3A%2F%2Fsinophibe.blogspot.com%2F2011%2F03%2Fph-calculation-of-very-small.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3APH" class="Z3988"></span></span> </li> <li id="cite_note-44"><span class="mw-cite-backlink"><b><a href="#cite_ref-44">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFBillo2011" class="citation book cs1">Billo, E.J. (2011). <i>EXCEL for Chemists</i> (3rd ed.). Wiley-VCH. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/978-0-470-38123-6" title="Special:BookSources/978-0-470-38123-6"><bdi>978-0-470-38123-6</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=EXCEL+for+Chemists&rft.edition=3rd&rft.pub=Wiley-VCH&rft.date=2011&rft.isbn=978-0-470-38123-6&rft.aulast=Billo&rft.aufirst=E.J.&rfr_id=info%3Asid%2Fen.wikipedia.org%3APH" class="Z3988"></span></span> </li> </ol></div></div> <div class="mw-heading mw-heading2"><h2 id="External_links">External links</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=PH&action=edit&section=24" title="Edit section: External links"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <style data-mw-deduplicate="TemplateStyles:r1235681985">.mw-parser-output .side-box{margin:4px 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.plainlist ol li,.mw-parser-output .plainlist ul li{margin-bottom:0}</style> <div class="side-box-flex"> <div class="side-box-image"><span class="noviewer" typeof="mw:File"><span><img alt="" src="//upload.wikimedia.org/wikipedia/commons/thumb/3/32/Scholia_logo.svg/40px-Scholia_logo.svg.png" decoding="async" width="40" height="39" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/3/32/Scholia_logo.svg/60px-Scholia_logo.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/3/32/Scholia_logo.svg/80px-Scholia_logo.svg.png 2x" data-file-width="107" data-file-height="104" /></span></span></div> <div class="side-box-text plainlist"><a href="https://www.wikidata.org/wiki/Wikidata:Scholia" class="extiw" title="d:Wikidata:Scholia">Scholia</a> has a profile for <a href="https://iw.toolforge.org/scholia/Q40936" class="extiw" title="toolforge:scholia/Q40936"><b>pH <small>(Q40936)</small></b></a>.</div></div> </div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1235681985"><style data-mw-deduplicate="TemplateStyles:r1237033735">@media print{body.ns-0 .mw-parser-output .sistersitebox{display:none!important}}@media screen{html.skin-theme-clientpref-night .mw-parser-output .sistersitebox img[src*="Wiktionary-logo-en-v2.svg"]{background-color:white}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .sistersitebox img[src*="Wiktionary-logo-en-v2.svg"]{background-color:white}}</style><div class="side-box side-box-right plainlinks sistersitebox"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1126788409"> <div class="side-box-flex"> <div class="side-box-image"><span class="noviewer" typeof="mw:File"><a href="/wiki/File:Wikidata-logo.svg" class="mw-file-description"><img alt="" src="//upload.wikimedia.org/wikipedia/commons/thumb/f/ff/Wikidata-logo.svg/40px-Wikidata-logo.svg.png" decoding="async" width="40" height="22" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/f/ff/Wikidata-logo.svg/60px-Wikidata-logo.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/f/ff/Wikidata-logo.svg/80px-Wikidata-logo.svg.png 2x" data-file-width="1050" data-file-height="590" /></a></span></div> <div class="side-box-text plainlist"><a href="/wiki/Wikidata" title="Wikidata">Wikidata</a> has the property: <ul><li><span class="mw-valign-middle" typeof="mw:File"><span><img alt="" src="//upload.wikimedia.org/wikipedia/commons/thumb/a/a8/Disc_Plain_blue_dark.svg/4px-Disc_Plain_blue_dark.svg.png" decoding="async" width="4" height="4" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/a/a8/Disc_Plain_blue_dark.svg/6px-Disc_Plain_blue_dark.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/a/a8/Disc_Plain_blue_dark.svg/8px-Disc_Plain_blue_dark.svg.png 2x" data-file-width="460" data-file-height="460" /></span></span> <b><i><a href="https://www.wikidata.org/wiki/Property_talk:P9440" class="extiw" title="d:Property talk:P9440">pH value (P9440)</a></i></b> (see <span class="plainlinks"><a class="external text" href="https://query.wikidata.org/embed.html#SELECT%20%3FWikidata_item_%20%3FWikidata_item_Label%20%3Fvalue%20%3FvalueLabel%20%3FEnglish_Wikipedia_article%20%23Show%20data%20in%20this%20order%0A%7B%0A%09%3FWikidata_item_%20wdt%3AP9440%20%3Fvalue%20.%20%23Collecting%20all%20items%20which%20have%20P9440%20data%2C%20from%20whole%20Wikidata%20item%20pages%0A%09OPTIONAL%20%7B%3FEnglish_Wikipedia_article%20schema%3Aabout%20%3FWikidata_item_%3B%20schema%3AisPartOf%20%3Chttps%3A%2F%2Fen.wikipedia.org%2F%3E%20.%7D%20%23If%20collected%20item%20has%20link%20to%20English%20Wikipedia%2C%20show%20that%0A%09SERVICE%20wikibase%3Alabel%20%7B%20bd%3AserviceParam%20wikibase%3Alanguage%20%22en%22%20%20%7D%20%23Show%20label%20in%20this%20language.%20%22en%22%20is%20English.%20%20%20%0A%7D%0ALIMIT%201000">uses</a></span>)</li></ul></div></div> </div> <ul><li><span class="noviewer" typeof="mw:File"><a href="/wiki/File:Wiktionary-logo-en-v2.svg" class="mw-file-description"><img alt="" src="//upload.wikimedia.org/wikipedia/commons/thumb/9/99/Wiktionary-logo-en-v2.svg/16px-Wiktionary-logo-en-v2.svg.png" decoding="async" width="16" height="16" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/9/99/Wiktionary-logo-en-v2.svg/24px-Wiktionary-logo-en-v2.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/9/99/Wiktionary-logo-en-v2.svg/32px-Wiktionary-logo-en-v2.svg.png 2x" data-file-width="512" data-file-height="512" /></a></span> The dictionary definition of <a href="https://en.wiktionary.org/wiki/%E3%8F%97" class="extiw" title="wiktionary:㏗"><i>pH</i></a> at Wiktionary</li> <li><span class="noviewer" typeof="mw:File"><a href="/wiki/File:Commons-logo.svg" class="mw-file-description"><img alt="" src="//upload.wikimedia.org/wikipedia/en/thumb/4/4a/Commons-logo.svg/12px-Commons-logo.svg.png" decoding="async" width="12" height="16" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/4/4a/Commons-logo.svg/18px-Commons-logo.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/4/4a/Commons-logo.svg/24px-Commons-logo.svg.png 2x" data-file-width="1024" data-file-height="1376" /></a></span> Media related to <a href="https://commons.wikimedia.org/wiki/Category:%E3%8F%97" class="extiw" title="commons:Category:㏗">pH</a> at Wikimedia Commons</li> <li><span class="noviewer" typeof="mw:File"><a href="/wiki/File:Wikiversity_logo_2017.svg" class="mw-file-description"><img alt="" src="//upload.wikimedia.org/wikipedia/commons/thumb/0/0b/Wikiversity_logo_2017.svg/16px-Wikiversity_logo_2017.svg.png" decoding="async" width="16" height="13" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/0/0b/Wikiversity_logo_2017.svg/24px-Wikiversity_logo_2017.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/0/0b/Wikiversity_logo_2017.svg/32px-Wikiversity_logo_2017.svg.png 2x" data-file-width="626" data-file-height="512" /></a></span> Learning materials related to <a href="https://en.wikiversity.org/wiki/Special:Search/PH" class="extiw" title="v:Special:Search/PH">PH</a> at Wikiversity</li></ul> <div class="navbox-styles"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374"><style data-mw-deduplicate="TemplateStyles:r1236075235">.mw-parser-output .navbox{box-sizing:border-box;border:1px solid #a2a9b1;width:100%;clear:both;font-size:88%;text-align:center;padding:1px;margin:1em auto 0}.mw-parser-output .navbox .navbox{margin-top:0}.mw-parser-output .navbox+.navbox,.mw-parser-output .navbox+.navbox-styles+.navbox{margin-top:-1px}.mw-parser-output .navbox-inner,.mw-parser-output .navbox-subgroup{width:100%}.mw-parser-output .navbox-group,.mw-parser-output .navbox-title,.mw-parser-output .navbox-abovebelow{padding:0.25em 1em;line-height:1.5em;text-align:center}.mw-parser-output .navbox-group{white-space:nowrap;text-align:right}.mw-parser-output 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href="/wiki/Bathroom" title="Bathroom">Bathroom</a></li> <li><a href="/wiki/Blackwater_(coal)" title="Blackwater (coal)">Blackwater (coal)</a></li> <li><a href="/wiki/Blackwater_(waste)" title="Blackwater (waste)">Blackwater (waste)</a></li> <li><a href="/wiki/Boiler_blowdown" title="Boiler blowdown">Boiler blowdown</a></li> <li><a href="/wiki/Brine" title="Brine">Brine</a></li> <li><a href="/wiki/Combined_sewer" title="Combined sewer">Combined sewer</a></li> <li><a href="/wiki/Cooling_tower#Wet_cooling_tower_material_balance" title="Cooling tower">Cooling tower</a></li> <li><a href="/wiki/Water_cooling" title="Water cooling">Cooling water</a></li> <li><a href="/wiki/Fecal_sludge_management" title="Fecal sludge management">Fecal sludge</a></li> <li><a href="/wiki/Greywater" title="Greywater">Greywater</a></li> <li><a href="/wiki/Infiltration/Inflow" title="Infiltration/Inflow">Infiltration/Inflow</a></li> <li><a href="/wiki/Industrial_wastewater_treatment#Sources_of_industrial_wastewater" title="Industrial wastewater treatment">Industrial wastewater</a></li> <li><a href="/wiki/Ion_exchange#Regeneration_wastewater" title="Ion exchange">Ion exchange</a></li> <li><a href="/wiki/Leachate" title="Leachate">Leachate</a></li> <li><a href="/wiki/Concentrated_animal_feeding_operation" title="Concentrated animal feeding operation">Manure</a></li> <li><a href="/wiki/Environmental_effects_of_paper#Water_pollution" class="mw-redirect" title="Environmental effects of paper">Papermaking</a></li> <li><a href="/wiki/Produced_water" title="Produced water">Produced water</a></li> <li><a href="/wiki/Return_flow" title="Return flow">Return flow</a></li> <li><a href="/wiki/Reverse_osmosis#Waste_stream_considerations" title="Reverse osmosis">Reverse osmosis</a></li> <li><a href="/wiki/Sanitary_sewer" title="Sanitary sewer">Sanitary sewer</a></li> <li><a href="/wiki/Septage" class="mw-redirect" title="Septage">Septage</a></li> <li><a href="/wiki/Sewage" title="Sewage">Sewage</a></li> <li><a href="/wiki/Sewage_sludge" title="Sewage sludge">Sewage sludge</a></li> <li><a href="/wiki/Toilet" title="Toilet">Toilet</a></li> <li><a href="/wiki/Urban_runoff" title="Urban runoff">Urban runoff</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Wastewater_quality_indicators" title="Wastewater quality indicators">Quality indicators</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Adsorbable_organic_halides" title="Adsorbable organic halides">Adsorbable organic halides</a></li> <li><a href="/wiki/Biochemical_oxygen_demand" title="Biochemical oxygen demand">Biochemical oxygen demand</a></li> <li><a href="/wiki/Chemical_oxygen_demand" title="Chemical oxygen demand">Chemical oxygen demand</a></li> <li><a href="/wiki/Coliform_index" title="Coliform index">Coliform index</a></li> <li><a href="/wiki/Oxygen_saturation" title="Oxygen saturation">Oxygen saturation</a></li> <li><a href="/wiki/Heavy_metals" title="Heavy metals">Heavy metals</a></li> <li><a class="mw-selflink selflink">pH</a></li> <li><a href="/wiki/Salinity" title="Salinity">Salinity</a></li> <li><a href="/wiki/Temperature" title="Temperature">Temperature</a></li> <li><a href="/wiki/Total_dissolved_solids" title="Total dissolved solids">Total dissolved solids</a></li> <li><a href="/wiki/Total_suspended_solids" title="Total suspended solids">Total suspended solids</a></li> <li><a href="/wiki/Turbidity" title="Turbidity">Turbidity</a></li> <li><a href="/wiki/Wastewater_surveillance" title="Wastewater surveillance">Wastewater surveillance</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Wastewater_treatment" title="Wastewater treatment">Treatment options</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Activated_sludge" title="Activated sludge">Activated sludge</a></li> <li><a href="/wiki/Aerated_lagoon" title="Aerated lagoon">Aerated lagoon</a></li> <li><a href="/wiki/Agricultural_wastewater_treatment" title="Agricultural wastewater treatment">Agricultural wastewater treatment</a></li> <li><a href="/wiki/API_oil%E2%80%93water_separator" title="API oil–water separator">API oil–water separator</a></li> <li><a href="/wiki/Carbon_filtering" title="Carbon filtering">Carbon filtering</a></li> <li><a href="/wiki/Water_chlorination" title="Water chlorination">Chlorination</a></li> <li><a href="/wiki/Clarifier" title="Clarifier">Clarifier</a></li> <li><a href="/wiki/Constructed_wetland" title="Constructed wetland">Constructed wetland</a></li> <li><a href="/wiki/Decentralized_wastewater_system" title="Decentralized wastewater system">Decentralized wastewater system</a></li> <li><a href="/wiki/Extended_aeration" title="Extended aeration">Extended aeration</a></li> <li><a href="/wiki/Facultative_lagoon" title="Facultative lagoon">Facultative lagoon</a></li> <li><a href="/wiki/Fecal_sludge_management" title="Fecal sludge management">Fecal sludge management</a></li> <li><a href="/wiki/Filtration" title="Filtration">Filtration</a></li> <li><a href="/wiki/Imhoff_tank" title="Imhoff tank">Imhoff tank</a></li> <li><a href="/wiki/Industrial_wastewater_treatment" title="Industrial wastewater treatment">Industrial wastewater treatment</a></li> <li><a href="/wiki/Ion_exchange" title="Ion exchange">Ion exchange</a></li> <li><a href="/wiki/Membrane_bioreactor" title="Membrane bioreactor">Membrane bioreactor</a></li> <li><a href="/wiki/Reverse_osmosis" title="Reverse osmosis">Reverse osmosis</a></li> <li><a href="/wiki/Rotating_biological_contactor" title="Rotating biological contactor">Rotating biological contactor</a></li> <li><a href="/wiki/Secondary_treatment" title="Secondary treatment">Secondary treatment</a></li> <li><a href="/wiki/Sedimentation_(water_treatment)" title="Sedimentation (water treatment)">Sedimentation</a></li> <li><a href="/wiki/Septic_tank" title="Septic tank">Septic tank</a></li> <li><a href="/wiki/Settling_basin" title="Settling basin">Settling basin</a></li> <li><a href="/wiki/Sewage_sludge_treatment" title="Sewage sludge treatment">Sewage sludge treatment</a></li> <li><a href="/wiki/Sewage_treatment" title="Sewage treatment">Sewage treatment</a></li> <li><a href="/wiki/Sewer_mining" title="Sewer mining">Sewer mining</a></li> <li><a href="/wiki/Stabilization_pond" class="mw-redirect" title="Stabilization pond">Stabilization pond</a></li> <li><a href="/wiki/Trickling_filter" title="Trickling filter">Trickling filter</a></li> <li><a href="/wiki/Ultraviolet_germicidal_irradiation" title="Ultraviolet germicidal irradiation">Ultraviolet germicidal irradiation</a></li> <li><a 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