Why Does Salt Melt Ice?

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Please refer to the appropriate style manual or other sources if you have any questions. </div> <div class="label mt-20 mb-10">Select Citation Style</div> <select class="js-citation-format-select form-select"> <option selected value="mla">MLA</option> <option value="apa">APA</option> <option value="chicago">Chicago Manual of Style</option> </select> <div class="citation font-serif border rounded p-15 mt-20" data-authors="Grannan, Cydney" data-authors-initial="Grannan, C." data-title="Why Does Salt Melt Ice?" data-published-date="24 Aug. 2016" data-url="https://www.britannica.com/story/why-does-salt-melt-ice" > <div class="citation-text"></div> </div> <button class="js-copy-citation-button mt-20 btn btn-xs btn-outline-blue border shadow-sm pr-10" > <em class="material-icons md-icon ml-n10 my-n5 mr-5" data-icon="file_copy"></em> <span class="js-citation-status-text">Copy Citation</span> </button> </div> </div> </div> <div> <button class="js-share-modal-button js-modal gtm-topic-tool btn btn-xs btn-outline-blue border shadow-sm pr-10" data-modal=".md-share-modal"> <em class="material-icons md-icon ml-n10 my-n5 mr-5" data-icon="share"></em> Share </button> <div class="md-share-modal size-lg d-none qa-share-modal"> <div class="md-modal-body"> <div class="h2 font-serif d-flex align-items-center pb-15 border-bottom"> <em class="material-icons text-blue mr-10" data-icon="share"></em> Share </div> <div class="label my-20">Share to social media</div> <div class="md-social-toolbar-circle d-flex align-items-start inverted" data-value="share" title="Why Does Salt Melt Ice?" data-url="https://www.britannica.com/story/why-does-salt-melt-ice" > <a class="social-icon facebook justify-content-center d-flex align-items-center align-self-center" data-provider="facebook" href="https://www.facebook.com/BRITANNICA/" target="_blank" rel="noopener"><span>Facebook</span></a> <a class="social-icon x justify-content-center d-flex align-items-center align-self-center" data-provider="x" href="https://x.com/britannica" target="_blank" rel="noopener"><span>X</span></a> </div> <div class="label pt-20 mt-20 mb-5 border-top">URL</div> <a class="font-serif text-truncate d-inline-block" href="https://www.britannica.com/story/why-does-salt-melt-ice">https://www.britannica.com/story/why-does-salt-melt-ice</a> </div> </div> </div> </div> <div class="md-byline module-spacing font-12"> <div class="font-serif font-12"> <span class="written-by text-gray-700"> Written by </span> <div class="editor-popover popover p-0"> <a class="d-block p-20 qa-editor-popup gtm-byline font-12 byline-contributor" href="/contributor/Cydney-Grannan/9781534" > <div class="editor-title font-16 font-weight-bold">Cydney Grannan</div> <div class="editor-description font-12 font-serif mt-5 clamp-description text-black">Cydney Grannan was an Editorial Intern at Encyclopædia Britannica. She received her B.A. in English from the University of Chicago in 2016.</div> </a> <div data-popper-arrow></div> </div> <span class="btn btn-link editor-link p-0 qa-byline-link gtm-byline font-12 byline-contributor text-decoration-underline"> Cydney Grannan</span></div> <div class="font-serif font-12 text-gray-700"> <span class="qa-fact-checked-by">Fact-checked by</span> <div class="editor-popover popover p-0"> <a class="d-block p-20 qa-editor-popup font-12" href="/editor/The-Editors-of-Encyclopaedia-Britannica/4419" > <div class="editor-title font-16 font-weight-bold">The Editors of Encyclopaedia Britannica</div> <div class="editor-description font-12 font-serif mt-5 text-black">Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree. They write new content and verify and edit content received from contributors.</div> </a> <div data-popper-arrow></div> </div> <span class="btn btn-link editor-link p-0 qa-byline-link font-12 "> The Editors of Encyclopaedia Britannica</span></div></div> </div> <article class="topic-content content mt-20"><figure class="md-assembly md-feature-assembly print-false" data-type="1" data-descid="1"><div class="md-assembly-wrapper card-media" data-type="image"><a href="https://cdn.britannica.com/15/191515-050-C5EE6821/winter-ice-salt-ground-background-pattern.jpg" target="_blank" class="gtm-assembly-link position-relative d-flex align-items-center justify-content-center " data-href="*"><img src="https://cdn.britannica.com/15/191515-050-C5EE6821/winter-ice-salt-ground-background-pattern.jpg?w=600&q=60" alt="winter ice melting salt on the ground, pattern as background" data-width="1600" data-height="1067" loading="eager"><button class="magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10" aria-label="Zoom in"><em class="material-icons link-blue" data-icon="zoom_in"></em></button></a></div><figcaption class=""><div class="md-assembly-caption text-muted font-14 font-serif line-clamp"><span><button class="js-more-btn d-none btn btn-unstyled font-12 bg-white js-content" aria-label="Toggle more/less fact data"><span class="link-blue">(more)</span></button></span></div><cite class="credit d-block mt-5">© nd700/Fotolia</cite></figcaption></figure><p class="topic-paragraph">More than 20 million tons of <a href="https://www.britannica.com/science/salt-acid-base-reactions" class="md-crosslink " data-show-preview="true">salt</a> are used every year to melt snow and ice in cold northern regions. But how does salt do it?</p><span class="MOD1"></span><p class="topic-paragraph">First, it’s important to understand a bit about H<sub>2</sub>O in the winter. Thirty-two degrees Fahrenheit (0 degrees Celsius) is its <a href="https://www.britannica.com/science/freezing-point" class="md-crosslink " data-show-preview="true">freezing point</a>—that is, when water reaches 32 °F, it turns into ice. At this temperature, your icy road generally has a thin layer of water on top of the ice, and the ice molecules and water molecules are interacting. This water is constantly melting some of the ice, while the ice beneath it is freezing some of the water. At this temperature, the exchange rate is pretty constant, meaning the amount of water and the amount of ice stay the same. If it gets colder, more water becomes ice. If it gets warmer, more ice becomes water. <strong>When the <a href="https://www.britannica.com/science/ionic-compound" class="md-crosslink " data-show-preview="true">ionic compound</a> salt is added to the equation, it lowers the freezing point of the water, which means the ice on the ground can’t freeze that layer of water at 32 °F anymore. The water, however, can still melt the ice at that temperature, which results in less ice on the roads.</strong> </p><span class="MOD2"></span><p class="topic-paragraph">But you may be asking how salt lowers the freezing point of water. This concept is called “freezing point depression.” Essentially, the salt makes it harder for the water molecules to bond together in their rigid structure. In water, salt is a solute, and it will break into its elements. So, if you’re using table salt, also known as <a href="https://www.britannica.com/science/salt" class="md-crosslink " data-show-preview="true">sodium chloride</a> (NaCl), to melt ice, the salt will dissolve into separate sodium <a href="https://www.britannica.com/science/ion-physics" class="md-crosslink " data-show-preview="true">ions</a> and chloride ions. Often, however, cities use calcium chloride (CaCl<sub>2</sub>), another type of salt, on their icy streets. Calcium chloride is more effective at melting ice because it can break down into three ions instead of two: one calcium ion and two chloride ions. More ions mean more ions getting in the way of those rigid ice bonds. </p><span class="MOD3"></span><p class="topic-paragraph">Unfortunately, chloride is superbad for the environment. It can kill aquatic animals, and that can thereby affect other animal populations in their <a href="https://www.britannica.com/science/food-web" class="md-crosslink " data-show-preview="true">food web</a>. Chloride also dehydrates and kills plants and can alter soil composition, making it harder for vegetation to grow. While some other compounds that can melt ice and snow don’t include chloride, they are much more expensive than sodium chloride or calcium chloride. </p><span class="MOD4"></span><span class="AM-END-OF-ARTICLE am-inline"></span></article> </div> </div> </div> <aside class="cm-rightrail d-none d-md-block ad-rail"></aside> </div> </div> </div> </div> </main> <div class="grid gx-0"> <div class="col"> <div class="md-loading hidden display-4 font-weight-normal"></div> <div class="text-center my-20 mb-100"> <button class="md-infinite-load-next btn btn-blue" data-value="next-page">Load More</button> </div> </div> <div class="col-md-da-320 hidden-xs"> </div> </div> </div> </div> </main> <div id="md-footer"></div> <noscript><iframe src="//www.googletagmanager.com/ns.html?id=GTM-5W6NC8" height="0" width="0" style="display:none;visibility:hidden"></iframe></noscript> <script type="text/javascript" id="_informizely_script_tag"> var IzWidget = IzWidget || {}; (function (d) { var scriptElement = d.createElement('script'); scriptElement.type = 'text/javascript'; scriptElement.async = true; scriptElement.src = "https://insitez.blob.core.windows.net/site/f780f33e-a610-4ac2-af81-3eb184037547.js"; var node = d.getElementById('_informizely_script_tag'); node.parentNode.insertBefore(scriptElement, node); } )(document); </script>  <script> window.ap3c = window.ap3c || {}; var ap3c = window.ap3c; ap3c.cmd = ap3c.cmd || []; ap3c.cmd.push(function() { ap3c.init('ZO4siT4cLwnykPnzZWJtd3Byb2Q', 'https://engage.email.britannica.com/'); ap3c.track({v: 0}); }); ap3c.activity = function(act) { ap3c.act = (ap3c.act || []); ap3c.act.push(act); }; var s, t; s = document.createElement('script'); s.type = 'text/javascript'; s.src = "https://engage.email.britannica.com/app.js"; t = document.getElementsByTagName('script')[0]; t.parentNode.insertBefore(s, t); </script> <script class="marketing-page-info" type="application/json"> {"pageType":"Story","templateName":"DEMYSTIFIED","pageNumber":1,"pagesTotal":11,"pageId":5881,"pageLength":null,"initialLoad":true,"lastPageOfScroll":false} </script> <script class="marketing-content-info" type="application/json"> [] </script> <script src="https://cdn.britannica.com/mendel-resources/3-133/js/libs/jquery-3.5.0.min.js?v=3.133.9"></script> <script type="text/javascript" data-type="Init Mendel Code Splitting"> (function() { $.ajax({ dataType: 'script', cache: true, url: 'https://cdn.britannica.com/mendel-resources/3-133/dist/story-page.js?v=3.133.9' }); })(); </script> <script class="analytics-metadata" type="application/json"> {"leg":"C","adLeg":"C","userType":"ANONYMOUS","pageType":"Story","pageSubtype":"DEMYSTIFIED","articleTemplateType":null,"gisted":false,"pageNumber":1,"hasSummarizeButton":false,"hasAskButton":false} </script> <script type="text/javascript"> EBStat={accountId:-1,hostnameOverride:'webstats.eb.com',domain:'www.britannica.com', json:''}; </script> <script type="text/javascript"> ( function() { $.ajax( { dataType: 'script', cache: true, url: '//www.britannica.com/webstats/mendelstats.js?v=1' } ) .done( function() { try {writeStat(null,EBStat);} catch(err){} } ); })(); </script> <div id="bc-fixed-dialogue"></div> </body> </html>

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Why Does Salt Melt Ice? | Britannica