Substances | Chemistry | Visionlearning

<!DOCTYPE html> <html lang="en" dir="ltr"> <head>  <meta http-equiv="X-UA-Compatible" content="ie=edge"> <meta charset="utf-8"> <base href="https://www.visionlearning.com"> <title>Substances | Chemistry | Visionlearning</title> <link rel="canonical" href="https://www.visionlearning.com/en/library/chemistry/1/substances/280"> <meta name="description" content="This module explores substances through hypothetical and real-world examples. Substances are broadly classified as pure substances, such as elements and compounds, or mixtures, such as rainwater, but the classification system goes further. How a substance is classified depends on its makeup and properties, and understanding the differences helps scientists solve major issues, such as creating clean drinking water."> <meta name="keywords" content="substance, substances, molecule, molecules, element, elements, compound, compounds, mixture, mixtures, atom, atoms"> <meta name="viewport" content="width=device-width, initial-scale=1.0, shrink-to-fit=no"> <meta name="msvalidate.01" content="D8E20F39AD48052260032E56DE409970"> <script type="application/ld+json"> { "@context": "http://schema.org/", "@type": "Article", "mainEntityOfPage": { "@type": "WebPage", "@id": "https://visionlearning.com/en/library/chemistry/1/substances/280" }, "name": "Substances", "headline": "Substances: Pure substances and mixtures", "author": { "@type": "Person", "name": "Judi Luepke, PhD." }, "datePublished": "2022-08-26 14:16:32", "dateModified": "2017-02-12T08:30:00+05:00", "image": { "@type": "ImageObject", "url": "/img/library/moduleImages/featured_image_280-23061209064709.jpg", "width": 696, "height": 464 }, "publisher": { "@type": "Organization", "name": "Visionlearning, Inc.", "logo": { "@type": "ImageObject", "url": "http://visionlearning.com/images/logo.png", "width": 278, "height": 60 } }, "description": "This module explores substances through hypothetical and real-world examples. Substances are broadly classified as pure substances, such as elements and compounds, or mixtures, such as rainwater, but the classification system goes further. How a substance is classified depends on its makeup and properties, and understanding the differences helps scientists solve major issues, such as creating clean drinking water.", "keywords": "substance, substances, molecule, molecules, element, elements, compound, compounds, mixture, mixtures, atom, atoms", "inLanguage": { "@type": "Language", "name": "English", "alternateName": "en" }, "copyrightHolder": { "@type": "Organization", "name": "Visionlearning, Inc." }, "copyrightYear": "2022"} </script> <meta property="og:url" content="https://visionlearning.com/en/library/chemistry/1/substances/280"> <meta property="og:title" content="Substances | Chemistry | Visionlearning" /> <meta property="og:type" content="website"> <meta property="og:site_name" content="Visionlearning"> <meta property="og:description" content="This module explores substances through hypothetical and real-world examples. Substances are broadly classified as pure substances, such as elements and compounds, or mixtures, such as rainwater, but the classification system goes further. How a substance is classified depends on its makeup and properties, and understanding the differences helps scientists solve major issues, such as creating clean drinking water."> <meta property="og:image" content="https://visionlearning.com/images/logo.png"> <meta property="fb:admins" content="100000299664514"> <link rel="stylesheet" type="text/css" href="/css/visionlearning.css">  <link rel="stylesheet" type="text/css" href="/css/visionlearning-icons.css">  <link rel="preload" href="https://fonts.gstatic.com"> <link rel="preload" href="https://fonts.googleapis.com/css2?family=Open+Sans:ital,wght@0,400;0,700;1,400;1,700&family=Schoolbell&display=swap"> <style> textarea.myEditor { width: 90%; height: 350px; } </style> <script type="text/x-mathjax-config" src="/js/mathjax-config.js"></script> <script id="MathJax-script" async src="/js/mathjax/tex-svg.js"></script> <script async src="https://pagead2.googlesyndication.com/pagead/js/adsbygoogle.js?client=ca-pub-9561344156007092" 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<li><a href="/en/library/environmental-science/61/ecosystem-services/279">Ecosystem Services</a></li> <li><a href="/en/library/environmental-science/61/population-biology/287">Population Biology</a></li> </ul> </div> <button class="accordion__button" id="acc-button-earth-cycles" data-accordion="button" aria-controls="acc-panel-earth-cycles" aria-expanded="false"> <span class="accordion__button__label"> Earth Cycles </span> </button> <div class="accordion__panel" id="acc-panel-earth-cycles" data-accordion="panel" aria-labelledby="acc-button-earth-cycles" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/environmental-science/61/the-nitrogen-cycle/98">The Nitrogen Cycle</a></li> <li><a href="/en/library/environmental-science/61/the-carbon-cycle/95">The Carbon Cycle</a></li> <li><a href="/en/library/environmental-science/61/the-phosphorus-cycle/197">The Phosphorus Cycle</a></li> </ul> </div> <button class="accordion__button" id="acc-button-scientific-research" 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aria-labelledby="acc-button-measurement" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/general-science/3/the-metric-system/47">The Metric System</a></li> </ul> </div> <button class="accordion__button" id="acc-button-physical-properties" data-accordion="button" aria-controls="acc-panel-physical-properties" aria-expanded="false"> <span class="accordion__button__label"> Physical Properties </span> </button> <div class="accordion__panel" id="acc-panel-physical-properties" data-accordion="panel" aria-labelledby="acc-button-physical-properties" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/general-science/3/temperature/48">Temperature</a></li> <li><a href="/en/library/general-science/3/density-and-buoyancy/37">Density and Buoyancy</a></li> </ul> </div> </div> </div> <button class="accordion__button" id="acc-button-math-in-science" data-accordion="button" aria-controls="acc-panel-math-in-science" aria-expanded="false"> <span 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href="/en/library/math-in-science/62/exponential-equations-ii/210">Exponential Equations II</a></li> <li><a href="/en/library/math-in-science/62/scientific-notation/250">Scientific Notation</a></li> <li><a href="/en/library/math-in-science/62/measurement/257">Measurement</a></li> </ul> </div> <button class="accordion__button" id="acc-button-statistics" data-accordion="button" aria-controls="acc-panel-statistics" aria-expanded="false"> <span class="accordion__button__label"> Statistics </span> </button> <div class="accordion__panel" id="acc-panel-statistics" data-accordion="panel" aria-labelledby="acc-button-statistics" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/math-in-science/62/introduction-to-descriptive-statistics/218">Introduction to Descriptive Statistics</a></li> <li><a href="/en/library/math-in-science/62/introduction-to-inferential-statistics/224">Introduction to Inferential Statistics</a></li> <li><a href="/en/library/math-in-science/62/statistical-techniques/239">Statistical Techniques</a></li> </ul> </div> <button class="accordion__button" id="acc-button-trigonometric-functions" data-accordion="button" aria-controls="acc-panel-trigonometric-functions" aria-expanded="false"> <span class="accordion__button__label"> Trigonometric Functions </span> </button> <div class="accordion__panel" id="acc-panel-trigonometric-functions" data-accordion="panel" aria-labelledby="acc-button-trigonometric-functions" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/math-in-science/62/wave-mathematics/131">Wave Mathematics</a></li> </ul> </div> </div> </div> <button class="accordion__button" id="acc-button-physics" data-accordion="button" aria-controls="acc-panel-physics" aria-expanded="false"> <span class="accordion__button__label"> Physics </span> </button> <div class="accordion__panel" id="acc-panel-physics" data-accordion="panel" aria-labelledby="acc-button-physics" role="region"> <div class="accordion accordion--secondary"> <button class="accordion__button" id="acc-button-light-and-optics" data-accordion="button" aria-controls="acc-panel-light-and-optics" aria-expanded="false"> <span class="accordion__button__label"> Light and Optics </span> </button> <div class="accordion__panel" id="acc-panel-light-and-optics" data-accordion="panel" aria-labelledby="acc-button-light-and-optics" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/physics/24/the-nature-of-light/132">The Nature of Light</a></li> <li><a href="/en/library/physics/24/electromagnetism-and-light/138">Electromagnetism and Light</a></li> </ul> </div> <button class="accordion__button" id="acc-button-mechanics" data-accordion="button" aria-controls="acc-panel-mechanics" aria-expanded="false"> <span class="accordion__button__label"> Mechanics </span> </button> <div class="accordion__panel" id="acc-panel-mechanics" data-accordion="panel" aria-labelledby="acc-button-mechanics" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/physics/24/defining-energy/199">Defining Energy</a></li> <li><a href="/en/library/physics/24/waves-and-wave-motion/102">Waves and Wave Motion</a></li> <li><a href="/en/library/physics/24/gravity/118">Gravity</a></li> <li><a href="/en/library/physics/24/thermodynamics-i/200">Thermodynamics I</a></li> </ul> </div> </div> </div> <button class="accordion__button" id="acc-button-process-of-science" data-accordion="button" aria-controls="acc-panel-process-of-science" aria-expanded="false"> <span class="accordion__button__label"> Process of Science </span> </button> <div class="accordion__panel" id="acc-panel-process-of-science" data-accordion="panel" aria-labelledby="acc-button-process-of-science" role="region"> <div class="accordion accordion--secondary"> <button class="accordion__button" id="acc-button-introduction" data-accordion="button" aria-controls="acc-panel-introduction" aria-expanded="false"> <span class="accordion__button__label"> Introduction </span> </button> <div class="accordion__panel" id="acc-panel-introduction" data-accordion="panel" aria-labelledby="acc-button-introduction" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/process-of-science/49/the-process-of-science/176">The Process of Science</a></li> </ul> </div> <button class="accordion__button" id="acc-button-the-culture-of-science" data-accordion="button" aria-controls="acc-panel-the-culture-of-science" aria-expanded="false"> <span class="accordion__button__label"> The Culture of Science </span> </button> <div class="accordion__panel" id="acc-panel-the-culture-of-science" data-accordion="panel" aria-labelledby="acc-button-the-culture-of-science" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/process-of-science/49/the-nature-of-scientific-knowledge/185">The Nature of Scientific Knowledge</a></li> <li><a href="/en/library/process-of-science/49/scientists-and-the-scientific-community/172">Scientists and the Scientific Community</a></li> <li><a href="/en/library/process-of-science/49/scientific-ethics/161">Scientific Ethics</a></li> <li><a href="/en/library/process-of-science/49/scientific-institutions-and-societies/162">Scientific Institutions and Societies</a></li> </ul> </div> <button class="accordion__button" id="acc-button-ideas-in-science" data-accordion="button" aria-controls="acc-panel-ideas-in-science" aria-expanded="false"> <span class="accordion__button__label"> Ideas in Science </span> </button> <div class="accordion__panel" id="acc-panel-ideas-in-science" data-accordion="panel" aria-labelledby="acc-button-ideas-in-science" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/process-of-science/49/theories-hypotheses-and-laws/177">Theories, Hypotheses, and Laws</a></li> <li><a href="/en/library/process-of-science/49/scientific-controversy/181">Scientific Controversy</a></li> <li><a href="/en/library/process-of-science/49/creativity-in-science/182">Creativity in Science</a></li> </ul> </div> <button class="accordion__button" id="acc-button-research-methods" data-accordion="button" aria-controls="acc-panel-research-methods" aria-expanded="false"> <span class="accordion__button__label"> Research Methods </span> </button> <div class="accordion__panel" id="acc-panel-research-methods" data-accordion="panel" aria-labelledby="acc-button-research-methods" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/process-of-science/49/the-practice-of-science/148">The Practice of Science</a></li> <li><a href="/en/library/process-of-science/49/experimentation-in-scientific-research/150">Experimentation in Scientific Research</a></li> <li><a href="/en/library/process-of-science/49/description-in-scientific-research/151">Description in Scientific Research</a></li> <li><a href="/en/library/process-of-science/49/comparison-in-scientific-research/152">Comparison in Scientific Research</a></li> <li><a href="/en/library/process-of-science/49/modeling-in-scientific-research/153">Modeling in Scientific Research</a></li> </ul> </div> <button class="accordion__button" id="acc-button-data" data-accordion="button" aria-controls="acc-panel-data" aria-expanded="false"> <span class="accordion__button__label"> Data </span> </button> <div class="accordion__panel" id="acc-panel-data" data-accordion="panel" aria-labelledby="acc-button-data" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/process-of-science/49/data-analysis-and-interpretation/154">Data Analysis and Interpretation</a></li> <li><a href="/en/library/process-of-science/49/uncertainty-error-and-confidence/157">Uncertainty, Error, and Confidence</a></li> <li><a href="/en/library/process-of-science/49/statistics-in-science/155">Statistics in Science</a></li> <li><a href="/en/library/process-of-science/49/using-graphs-and-visual-data-in-science/156">Using Graphs and Visual Data in Science</a></li> </ul> </div> <button class="accordion__button" id="acc-button-scientific-communication" data-accordion="button" aria-controls="acc-panel-scientific-communication" aria-expanded="false"> <span class="accordion__button__label"> Scientific Communication </span> </button> <div class="accordion__panel" id="acc-panel-scientific-communication" data-accordion="panel" aria-labelledby="acc-button-scientific-communication" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/process-of-science/49/understanding-scientific-journals-and-articles/158">Understanding Scientific Journals and Articles</a></li> <li><a href="/en/library/process-of-science/49/utilizing-the-scientific-literature/173">Utilizing the Scientific Literature</a></li> <li><a href="/en/library/process-of-science/49/peer-review-in-scientific-publishing/159">Peer Review in Scientific Publishing</a></li> <li><a href="/en/library/process-of-science/49/the-how-and-why-of-scientific-meetings/186">The How and Why of Scientific Meetings</a></li> </ul> </div> </div> </div> <button class="accordion__button" id="acc-button-scientists-and-research" data-accordion="button" aria-controls="acc-panel-scientists-and-research" aria-expanded="false"> <span class="accordion__button__label"> Scientists and Research </span> </button> <div class="accordion__panel" id="acc-panel-scientists-and-research" data-accordion="panel" aria-labelledby="acc-button-scientists-and-research" role="region"> <div class="accordion accordion--secondary"> <button class="accordion__button" id="acc-button-scientific-research" data-accordion="button" aria-controls="acc-panel-scientific-research" aria-expanded="false"> <span class="accordion__button__label"> Scientific Research </span> </button> <div class="accordion__panel" id="acc-panel-scientific-research" data-accordion="panel" aria-labelledby="acc-button-scientific-research" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/scientists-and-research/58/collaborative-research-in-the-arctic-towards-understanding-climate-change/183">Collaborative Research in the Arctic Towards Understanding Climate Change</a></li> <li><a href="/en/library/scientists-and-research/58/from-stable-chromosomes-to-jumping-genes/184">From Stable Chromosomes to Jumping Genes</a></li> <li><a href="/en/library/scientists-and-research/58/an-elegant-experiment-to-test-the-process-of-dna-replication/187">An Elegant Experiment to Test the Process of DNA Replication</a></li> <li><a href="/en/library/scientists-and-research/58/the-founding-of-neuroscience/233">The Founding of Neuroscience</a></li> <li><a href="/en/library/scientists-and-research/58/tracking-endangered-jaguars-across-the-border/189">Tracking Endangered Jaguars across the Border</a></li> <li><a href="/en/library/scientists-and-research/58/atmospheric-chemistry-research-that-changed-global-policy/211">Atmospheric Chemistry Research that Changed Global Policy</a></li> <li><a href="/en/library/scientists-and-research/58/revolutionizing-medicine-with-monoclonal-antibodies/220">Revolutionizing Medicine with Monoclonal Antibodies</a></li> <li><a href="/en/library/scientists-and-research/58/uncovering-the-mysteries-of-chronic-mountain-sickness/238">Uncovering the Mysteries of Chronic Mountain Sickness</a></li> </ul> </div> <button class="accordion__button" id="acc-button-profiles-in-science" data-accordion="button" aria-controls="acc-panel-profiles-in-science" aria-expanded="false"> <span class="accordion__button__label"> Profiles in Science </span> </button> <div class="accordion__panel" id="acc-panel-profiles-in-science" data-accordion="panel" aria-labelledby="acc-button-profiles-in-science" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/scientists-and-research/58/luis-e.-miramontes/232">Luis E. Miramontes</a></li> <li><a href="/en/library/scientists-and-research/58/bernardo-houssay/237">Bernardo Houssay</a></li> <li><a href="/en/library/scientists-and-research/58/craig-lee/256">Craig Lee</a></li> <li><a href="/en/library/scientists-and-research/58/david-ho/241">David Ho</a></li> <li><a href="/en/library/scientists-and-research/58/louis-tompkins-wright/244">Louis Tompkins Wright</a></li> <li><a href="/en/library/scientists-and-research/58/carlos-j.-finlay/217">Carlos J. Finlay</a></li> <li><a href="/en/library/scientists-and-research/58/cecilia-payne/290">Cecilia Payne</a></li> <li><a href="/en/library/scientists-and-research/58/jazmin-scarlett/291">Jazmin Scarlett</a></li> <li><a href="/en/library/scientists-and-research/58/ramari-stewart/292">Ramari Stewart</a></li> <li><a href="/en/library/scientists-and-research/58/johnson-cerda/300">Johnson Cerda</a></li> <li><a href="/en/library/scientists-and-research/58/ellen-ochoa/201">Ellen Ochoa</a></li> <li><a href="/en/library/scientists-and-research/58/ruth-benerito/205">Ruth Benerito</a></li> <li><a href="/en/library/scientists-and-research/58/franklin-chang-díaz/219">Franklin Chang Díaz</a></li> <li><a href="/en/library/scientists-and-research/58/percy-lavon-julian/221">Percy Lavon Julian</a></li> <li><a href="/en/library/scientists-and-research/58/luis-walter-alvarez/229">Luis Walter Alvarez</a></li> <li><a href="/en/library/scientists-and-research/58/france-anne-dominic-córdova/230">France Anne-Dominic Córdova</a></li> </ul> </div> </div> </div> </div> </div> </li> <li>  <button class="button" data-toggle="dropdown">Chemistry </button> <div class="nav__dropdown box-shadow-1 padding-1"> <div class="accordion accordion--secondary font-size-sm"> <div class="accordion accordion--secondary"> <button class="accordion__button" id="acc-sub-button-atomic-theory-and-structure" data-accordion="button" aria-controls="acc-sub-panel-atomic-theory-and-structure" aria-expanded="false"> <span class="accordion__button__label"> Atomic Theory and Structure </span> </button> <div class="accordion__panel" id="acc-sub-panel-atomic-theory-and-structure" data-accordion="panel" aria-labelledby="acc-sub-button-atomic-theory-and-structure" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/chemistry/1/early-ideas-about-matter/49">Early Ideas about Matter</a></li> <li><a href="/en/library/chemistry/1/the-periodic-table-of-elements-i/52">The Periodic Table of Elements I</a></li> <li><a href="/en/library/chemistry/1/the-periodic-table-of-elements-ii/296">The Periodic Table of Elements II</a></li> <li><a href="/en/library/chemistry/1/the-periodic-table-of-elements-iii/297">The Periodic Table of Elements III</a></li> <li><a href="/en/library/chemistry/1/the-periodic-table-of-elements-iv/298">The Periodic Table of Elements IV</a></li> <li><a href="/en/library/chemistry/1/the-periodic-table-of-elements-v/299">The Periodic Table of Elements V</a></li> <li><a href="/en/library/chemistry/1/atomic-theory-i/50">Atomic Theory I</a></li> <li><a href="/en/library/chemistry/1/atomic-theory-ii/51">Atomic Theory II</a></li> <li><a href="/en/library/chemistry/1/atomic-theory-iii/223">Atomic Theory III</a></li> <li><a href="/en/library/chemistry/1/atomic-theory-iv/231">Atomic Theory IV</a></li> <li><a href="/en/library/chemistry/1/the-mole-and-atomic-mass/53">The Mole and Atomic Mass</a></li> </ul> </div> <button class="accordion__button" id="acc-sub-button-physical-states-and-properties" data-accordion="button" aria-controls="acc-sub-panel-physical-states-and-properties" aria-expanded="false"> <span class="accordion__button__label"> Physical States and Properties </span> </button> <div class="accordion__panel" id="acc-sub-panel-physical-states-and-properties" data-accordion="panel" aria-labelledby="acc-sub-button-physical-states-and-properties" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/chemistry/1/states-of-matter/120">States of Matter</a></li> <li class="current">Substances</li> <li><a href="/en/library/chemistry/1/properties-of-solids/209">Properties of Solids</a></li> <li><a href="/en/library/chemistry/1/properties-of-liquids/222">Properties of Liquids</a></li> <li><a href="/en/library/chemistry/1/properties-of-gases/245">Properties of Gases</a></li> <li><a href="/en/library/chemistry/1/diffusion-i/216">Diffusion I</a></li> <li><a href="/en/library/chemistry/1/kinetic-molecular-theory/251">Kinetic-Molecular Theory</a></li> <li><a href="/en/library/chemistry/1/solutions/266">Solutions</a></li> <li><a href="/en/library/chemistry/1/water/267">Water</a></li> </ul> </div> <button class="accordion__button" id="acc-sub-button-chemical-relationships" data-accordion="button" aria-controls="acc-sub-panel-chemical-relationships" aria-expanded="false"> <span class="accordion__button__label"> Chemical Relationships </span> </button> <div class="accordion__panel" id="acc-sub-panel-chemical-relationships" data-accordion="panel" aria-labelledby="acc-sub-button-chemical-relationships" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/chemistry/1/chemical-bonding/55">Chemical Bonding</a></li> <li><a href="/en/library/chemistry/1/stoichiometry/270">Stoichiometry</a></li> <li><a href="/en/library/chemistry/1/chemical-equations/268">Chemical Equations</a></li> <li><a href="/en/library/chemistry/1/acids-and-bases-i/271">Acids and Bases I</a></li> <li><a href="/en/library/chemistry/1/acids-and-bases-ii/272">Acids and Bases II</a></li> </ul> </div> <button class="accordion__button" id="acc-sub-button-reactions-and-changes" data-accordion="button" aria-controls="acc-sub-panel-reactions-and-changes" aria-expanded="false"> <span class="accordion__button__label"> Reactions and Changes </span> </button> <div class="accordion__panel" id="acc-sub-panel-reactions-and-changes" data-accordion="panel" aria-labelledby="acc-sub-button-reactions-and-changes" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/chemistry/1/chemical-reactions/54">Chemical Reactions</a></li> <li><a href="/en/library/chemistry/1/chemical-reactions-ii/278">Chemical Reactions II</a></li> <li><a href="/en/library/chemistry/1/nuclear-chemistry-i/284">Nuclear Chemistry I</a></li> <li><a href="/en/library/chemistry/1/carbon-chemistry/60">Carbon Chemistry</a></li> </ul> </div> </div> </div> </div> </li> </ul> </nav>  <div id="theTop"></div> <main id="skip-header-content"> <div class="margin-bottom-5"> <article class="container wide module"> <header class="grid grid--sidebar-right module__header"> <div class="module__header__title"> <span class="subcategory"> <strong><em>Physical States and Properties</em></strong> </span> <h1>Substances: <sub><em>Pure substances and mixtures</em></sub></h1> <p class="byline">by Judi Luepke, PhD.</p> <nav class="module__header__tabs"> <ul class="tabs-nav tabs-nav--horizontal library"> <li> <a href="/en/library/chemistry/1/substances/280/reading" aria-current="page" >Reading</a> </li> <li> <a href="/en/library/chemistry/1/substances/280/quiz">Quiz</a> </li> <li> <a href="/en/library/chemistry/1/substances/280/resources">Teach with this</a> </li> </ul> </nav> </div> <script type="application/ld+json"> { "@context": "http://schema.org", "@type": "AudioObject", "contentUrl": "https://www.visionlearning.com/img/library/moduleAudio/module_280.mp3", "description": "Recording of Substances : This module explores substances through hypothetical and real-world examples. Substances are broadly classified as pure substances, such as elements and compounds, or mixtures, such as rainwater, but the classification system goes further. How a substance is classified depends on its makeup and properties, and understanding the differences helps scientists solve major issues, such as creating clean drinking water.", "encodingFormat": "mp3", "name": "module_280.mp3" } </script> <div class="module_header_audio"> <div class="audio-player border border-radius"> <audio id="audio"> <source src="https://www.visionlearning.com/img/library/moduleAudio/module_280.mp3" type="audio/mpeg"> Your browser does not support the audio element. </audio> <div class="audio-player__title"> <p>Listen to this reading</p> <span class="audio-player__timestamp" id="timestamp"> 00:00 </span> </div> <div class="audio-player__controls" id="controls"> <button class="button button--icon-only" id="play-pause-button"> <span class="icon icon-play" aria-hidden="true"></span> </button> <div class="audio-player__progress" id="progress-bar" tabindex="0" aria-valuemin="0" aria-valuemax="100" aria-valuenow="0" aria-label="Use arrow keys to forward or rewind the audio" role="slider"> <div class="audio-player__progress__fill"> <span class="audio-player__thumb"></span> </div> </div> <div class="audio-player__volume-container"> <button id="mute-button"> <span class="icon icon-volume"></span> </button> <div class="audio-player__volume" tabindex="0" aria-valuemin="0" aria-valuemax="100" aria-valuenow="100" aria-label="Use arrow keys to adjust volume" role="slider"> <div class="audio-player__volume__fill"> <span class="audio-player__thumb"></span> </div> </div> </div> </div> </div> </div> </header> <hr class="divider"/>   <div class="grid grid--sidebar-right grid--divider"> <div class="order-2 order-1--lg module__main"> <div class="narrow margin-x-auto margin-y-5"> <div class="accordion margin-bottom-5">  <button class="accordion__button" id="acc-button-key-concepts" data-accordion="button" aria-controls="acc-panel-key-concepts" aria-expanded="true" tabindex="0"> Did you know? </button> <div class="accordion__panel shown show" id="acc-panel-key-concepts" data-accordion="panel" aria-labelledby="acc-button-key-concepts" role="region"> <div class="accordion__panel__content"> <p>Did you know that you encounter and interact with a variety of substances on a daily basis? Substances are everywhere and can vary significantly, from the water you drink to your favorite breakfast meal. Given that there are so many, how do scientists keep all of these substances straight? Let’s find out.</p> </div> </div>  <button class="accordion__button" id="acc-button-table-of-contents" data-accordion="button" aria-controls="acc-panel-table-of-contents" aria-expanded="false" tabindex="0"> Key concepts </button> <div class="accordion__panel" id="acc-panel-table-of-contents" data-accordion="panel" aria-labelledby="acc-button-table-of-contents" role="region" aria-hidden="true"> <div class="accordion__panel__content"> <ul class="bulleted"> <li><p>Substances can be classified as pure substances or mixtures. This classification helps scientists understand what particular substances are made up of and their properties.</p></li> <li><p>Experiments over many years have helped scientists recognize that pure substances include elements, which cannot be broken down, and compounds, which can be broken down chemically into the elements that make them up. Compounds have a definite composition and are chemically formed.</p></li> <li><p>Mixtures are physical combinations of pure substances that can be homogeneous or heterogeneous. Homogeneous mixtures are also called solutions and look the same throughout. Heterogeneous mixtures have clearly distinguished parts. </p></li> <li><p>Mixtures do not have a definite composition and may be separated physically, such as the distillation of water to separate salts and impurities from pure water. </p></li> <li><p>Elements are made up of atoms and compounds are made up of molecules. Mixtures may be any combination of atoms, molecules, or a combination of the two. </p></li> </ul> </div> </div>  <button class="accordion__button" id="acc-button-terms-you-should-know" data-accordion="button" aria-controls="acc-panel-terms-you-should-know" aria-expanded="false" tabindex="0"> Terms you should know </button> <div class="accordion__panel" id="acc-panel-terms-you-should-know" data-accordion="panel" aria-labelledby="acc-button-terms-you-should-know" role="region" aria-hidden="true"> <div class="accordion__panel__content"> <dl> <dt><a href="/en/glossary/view/molecule">Molecule </a></dt> <dd> A particle formed from the bonding of two or more atoms. </dd> <dt><a href="/en/glossary/view/atom">Atom </a></dt> <dd> The smallest unit of an element that retains the chemical properties of the element. </dd> <dt><a href="/en/glossary/view/element">Element </a></dt> <dd> A substance composed of atoms with identical atomic numbers.</dd> </dl> </div> </div> </div> <hr class="border-color-dark" /> <section> <div class="container narrow"> <p>Think of all the amazing substances you use during the first hours of your day. You take a shower with soap and water. You eat your favorite breakfast cereal and brush your teeth with toothpaste. On your way to class, you may grab a drink in an aluminum can from a vending machine. </p> <p>What are these substances made from? What makes them similar or different from one another? Let’s find out, beginning with a substance you use so often that you probably take it for granted: water.</p> <p><section id="toc_1" class=""> <h2>Water as a substance</h2></p> <p>Have you ever thought about what you are drinking when you drink a glass of water? Take a look at the two glasses in Figure 1. What do they contain? They contain a clear <mark class="term" data-term="liquid" data-term-def="The state of matter characterized by its condensed nature and ability to flow. Unlike gases, molecules within a liquid often experience&hellip;" data-term-url="/en/glossary/view/liquid/8727">liquid</mark> that looks like water. But is the water identical in the two glasses? </p> <div class="figure"> <figure> <button class="lightbox-button lightbox-button--icon" data-lightbox=""> <img src="/img/library/modules/mid280/Image/VLObject-12509-22081901085338.png" alt="Figure 1: Two glasses of water, Glass A and Glass B, that appear the same. Are they the same?" /> </button> <figcaption> <p><strong>Figure 1:</strong> Two glasses of water, Glass A and Glass B, that appear the same. Are they the same?</p> <span class="credit">image ©<a href="https://www.google.com/url?q=https://commons.wikimedia.org/wiki/File:Glass_Half_Full_bw_1_cropped_and_smaller.jpg&sa=D&source=docs&ust=1660762772115851&usg=AOvVaw0ZjtGhbMeSC3II7yn430fO"> CC BY-SA 3.0 S Nova</a> </span> </figcaption> </figure> </div> <p>You can't really tell any differences between the water in the two glasses using your naked eye. However, if you were able to view them at the molecular level, you might see something as shown in Figure 2. </p> <div class="figure"> <figure> <button class="lightbox-button lightbox-button--icon" data-lightbox=""> <img src="/img/library/modules/mid280/Image/VLObject-12511-22081901085647.png" alt="Figure 2: A model of the water in Glass A and in Glass B as viewed at the molecular level. Glass A contains only one type of molecule, while glass B contains a mixture of elements and molecules." /> </button> <figcaption> <p><strong>Figure 2:</strong> A model of the water in Glass A and in Glass B as viewed at the molecular level. Glass A contains only one type of molecule, while glass B contains a mixture of elements and molecules.</p> </figcaption> </figure> </div> <p>In what ways are the <mark class="term" data-term="model" data-term-def="A representation, pattern, or mathematical description that can help scientists replicate a system." data-term-url="/en/glossary/view/model/8236">models</mark> of water in Glass A and B similar? In what ways are they different?</p> <p>First, consider Glass A. Glass A contains water “molecules” that all look the same. <mark class="term" data-term="molecule" data-term-def="A particle formed by the chemical bonding of two or more atoms. The molecule is the smallest particle of a&hellip;" data-term-url="/en/glossary/view/molecule/1518">Molecules</mark> are formed by the chemical <mark class="term" data-term="bonding" data-term-def="The act of fastening two atoms together." data-term-url="/en/glossary/view/bonding/8295">bonding</mark> of two or more “atoms,” and <mark class="term" data-term="atom" data-term-def="The smallest unit of an element that retains the chemical properties of the element. Atoms can exist alone or in&hellip;" data-term-url="/en/glossary/view/atom/1509">atoms</mark> are the smallest <mark class="term" data-term="particle" data-term-def="A tiny piece of matter." data-term-url="/en/glossary/view/particle/8259">particles</mark> of “elements.” An exception are <mark class="term" data-term="diatomic" data-term-def="A molecule that contains two atoms. All of the non-inert gases occur as diatomic molecules: H<sub>2</sub>, O<sub>2</sub>, N<sub>2</sub>, F<sub>2</sub>, and Cl<sub>2</sub>." data-term-url="/en/glossary/view/diatomic/1557">diatomic</mark> molecules formed by some <mark class="term" data-term="element" data-term-def="One of fewer than 118 pure chemical substances. An element is a substance composed of atoms with identical atomic number." data-term-url="/en/glossary/view/element/1510">elements</mark> when existing alone in nature, such as nitrogen <mark class="term" data-term="gas" data-term-def="The state of matter characterized by its non-condensed nature and ability to flow. Unlike liquids, molecules within a gas remain far&hellip;" data-term-url="/en/glossary/view/gas/8725">gas</mark> existing as N<sub>2</sub>.</p> <p>Do you know the chemical <mark class="term" data-term="formula" data-term-def="An expression of the composition of a chemical compound using symbols." data-term-url="/en/glossary/view/formula/8554">formula</mark> for water? It is H<sub>2</sub>O, meaning that two atoms of the element hydrogen are bonded to one atom of the element oxygen to form each molecule of water. In Figure 2, the white spheres represent hydrogen atoms, and the red spheres represent oxygen atoms. These molecules collectively make up the “compound,” water. </p> <p>The depiction of water in Glass A (Figure 2) is considered a “pure substance” because only water molecules are present. <mark class="term" data-term="pure substances" data-term-def="matter with a definite composition and unique properties, including elements and compounds. For example, hydrogen and oxygen are elements but when&hellip;" data-term-url="/en/glossary/view/pure+substances/12621">Pure substances</mark> can be made up of atoms or molecules. Atoms are the smallest parts of elements - pure substances found on the periodic table. They cannot be chemically made or separated. Pure substances made up of molecules are called <mark class="term" data-term="compound" data-term-def="A material formed by the chemical combination of elements in defined proportions. Compounds can be chemically decomposed into simpler substances." data-term-url="/en/glossary/view/compound/1517">compounds</mark>. Compounds are chemically made and can only be chemically separated. </p> <p>Now look at Glass B. Glass B contains molecules of water mixed with atoms of elements. This water is not pure but part of a mixture. The blue and green spheres in the model represent atoms or <mark class="term" data-term="ion" data-term-def="An atom or molecule that has acquired an electrical charge by either gaining or losing electrons. A cation is an ion&hellip;" data-term-url="/en/glossary/view/ion/853">ions</mark> (atoms that have lost or gained <mark class="term" data-term="electron" data-term-def="A subatomic particle with a negative charge of 1.60 × 10<sup>-19</sup> coulombs and a mass of 9.11 × 10<sup>-31</sup> kg. Electrons&hellip;" data-term-url="/en/glossary/view/electron/852">electrons</mark> to become charged) of other elements. To figure out the elements, you should know that Glass B contains tap water, which can come from a lake, river, or <mark class="term" data-term="groundwater" data-term-def="Water that fills pore space in rocks and sediments and forms a subsurface aquifer. Groundwater is distinct from soil moisture, which&hellip;" data-term-url="/en/glossary/view/groundwater/2119">groundwater</mark> source. Tap water is filtered at a water <mark class="term" data-term="treatment" data-term-def="In science, a treatment refers to a method for fixing or manipulating an independent variable in the course of scientific research.&hellip;" data-term-url="/en/glossary/view/treatment/3799">treatment</mark> plant to remove many particles from the mixture. Then it is disinfected with the addition of compounds that release chloride <mark class="term" data-term="ion" data-term-url="/en/glossary/view/ion" data-term-def="An atom or molecule that has acquired an electrical charge by either gaining or losing electrons. A cation is an ion&hellip;">ions</mark>. Additionally, fluoride ions are often similarly added to tap water to reduce tooth <mark class="term" data-term="decay" data-term-def="To break down; to decrease over time in size, amount, or force." data-term-url="/en/glossary/view/decay/8265">decay</mark>. The blue and green spheres in Glass B represent chloride and fluoride ions. Because the particles in the model do not all look the same, Glass B is a model of a mixture. <mark class="term" data-term="mixtures" data-term-def="two or more pure substances combined that retain their unique properties. Mixtures include homogeneous mixtures, also called or solutions, where one&hellip;" data-term-url="/en/glossary/view/mixtures/12622">Mixtures</mark> can be made up of atoms, molecules, or a combination of both. Additionally, mixtures are physically mixed and can be physically separated. The atoms, molecules, or a combination of the two mixed together do not change but retain their unique characteristics and simply exist in a shared space.</p> <div class="comprehension-checkpoint margin-y-4"> <h6 class="comprehension-checkpoint__header"> <span> <span class="icon icon-question"></span> </span> Comprehension Checkpoint </h6> <form class="" name="cc12513"> <div class="form-entry"> <div class="form-entry__field"> <span class="form-entry__field__label">What is another name for a pure substance made up of one type of atom?</span> <div class="form-entry__option"> <div class="form-entry__option__radio" data-answer="correct"> <label> <input id="q1-12513-0-option-a" name="quiz-option-12513" type="radio" value="Element" > <span class="option__label"> <span class="screen-reader-only">a.</span> Element </span> </label> <span class="quiz__response" id="response-12513-0"> <strong>Correct!</strong> </span> </div> <div class="form-entry__option__radio" data-answer="incorrect"> <label> <input id="q1-12513-1-option-b" name="quiz-option-12513" type="radio" value="Molecule" > <span class="option__label"> <span class="screen-reader-only">b.</span> Molecule </span> </label> <span class="quiz__response" id="response-12513-1"> <strong>Incorrect.</strong> </span> </div> </div> </div> </div> </form> </div> <p>You learned that water is considered a pure substance when it consists of only water <mark class="term" data-term="molecule" data-term-def="A particle formed by the chemical bonding of two or more atoms. The molecule is the smallest particle of a&hellip;" data-term-url="/en/glossary/view/molecule/1518">molecules</mark> and nothing else. While you can drink this water, you may not like its taste. It does not have any flavor because there are no <mark class="term" data-term="mineral" data-term-def="A naturally formed, inorganic solid with a specific chemical composition and characteristic crystal structure. Examples of minerals include quartz (SiO<sub>2</sub>), salt&hellip;" data-term-url="/en/glossary/view/mineral/2978">minerals</mark> in it. This type of water can be made through “distillation” or other purification techniques. In the <mark class="term" data-term="distillation" data-term-def="the physical process of purifying a liquid by evaporation and condensation. For example, saltwater can be distilled to separate salt molecules&hellip;" data-term-url="/en/glossary/view/distillation/12620">distillation</mark> <mark class="term" data-term="process" data-term-def="Method, procedure; series of actions or steps." data-term-url="/en/glossary/view/process/8256">process</mark>, water is heated to form steam through evaporation. The impurities remain behind. Then steam is cooled to form distilled water through <mark class="term" data-term="condensation" data-term-def="The process of forming a liquid from a gas." data-term-url="/en/glossary/view/condensation/8561">condensation</mark>.</p> <p>Figure 3 shows the distillation process in the laboratory setting. Water is boiled in the round-bottom flask on the left. The steam travels upward and down the narrow tube on the right into the condenser. Cold water is forced through the outer part of the condenser tube to cool the steam in the narrow tube. Distilled water drips from the narrow tube into the flask on the right. </p> <div class="figure"> <figure> <button class="lightbox-button lightbox-button--icon" data-lightbox=""> <img src="/img/library/modules/mid280/Image/VLObject-12538-22081902084318.png" alt="Figure 3: The distillation process to purify water. Water, in the flask on the left, is boiled and condenses in the long tube leaving impurities behind." /> </button> <figcaption> <p><strong>Figure 3:</strong> The distillation process to purify water. Water, in the flask on the left, is boiled and condenses in the long tube leaving impurities behind.</p> <span class="credit">image ©<a href="https://commons.wikimedia.org/wiki/File:Fractional_distillation_lab_apparatus_blank_version.svg"> CC BY-SA 3.0 William Crochot</a> </span> </figcaption> </figure> </div> </section> <section id="toc_2"> <h2>Which water do we drink?</h2><p>You also learned that water is a mixture when it consists of water <mark class="term" data-term="molecule" data-term-def="A particle formed by the chemical bonding of two or more atoms. The molecule is the smallest particle of a&hellip;" data-term-url="/en/glossary/view/molecule/1518">molecules</mark> and other <mark class="term" data-term="atom" data-term-def="The smallest unit of an element that retains the chemical properties of the element. Atoms can exist alone or in&hellip;" data-term-url="/en/glossary/view/atom/1509">atoms</mark> or <mark class="term" data-term="ion" data-term-def="An atom or molecule that has acquired an electrical charge by either gaining or losing electrons. A cation is an ion&hellip;" data-term-url="/en/glossary/view/ion/853">ions</mark>, like chloride and fluoride. The water we drink is a mixture. Remember that water can come from a lake, river, or <mark class="term" data-term="groundwater" data-term-def="Water that fills pore space in rocks and sediments and forms a subsurface aquifer. Groundwater is distinct from soil moisture, which&hellip;" data-term-url="/en/glossary/view/groundwater/2119">groundwater</mark> source. It is mixed with lots of substances: dust, chemicals, <mark class="term" data-term="parasite" data-term-def="An organism that lives on or in a host organism of another species. Parasites derive their food from and are detrimental&hellip;" data-term-url="/en/glossary/view/parasite/5272">parasites</mark>, <mark class="term" data-term="bacteria" data-term-def="(plural of bacterium) A large group of one-celled organisms that are found almost everywhere." data-term-url="/en/glossary/view/bacteria/8679">bacteria</mark>, viruses, and more. It must be filtered and disinfected at a water <mark class="term" data-term="treatment" data-term-def="In science, a treatment refers to a method for fixing or manipulating an independent variable in the course of scientific research.&hellip;" data-term-url="/en/glossary/view/treatment/3799">treatment</mark> plant to make it safe for your consumption. But when did humans figure out the need to filter and disinfect water?</p> <p>Ancient Greek, Egyptian, and Sanskrit writings indicate that water was filtered as early as 2000 <mark class="term" data-term="BCE" data-term-def="An abbreviation for Before the Common Era, which is a designation for the years prior to year 1 of the Gregorian&hellip;" data-term-url="/en/glossary/view/BCE/3720">BCE</mark>. Historical <mark class="term" data-term="record" data-term-def="A written account or description. <br> <b>[verb]</b> To write an account or description." data-term-url="/en/glossary/view/record/8239">records</mark> and archaeological sites have indicated that water was treated in ancient Egypt, which is located in the Sahara Desert. Ancient Egyptians harvested rainwater. Rainwater was naturally purified and safe for drinking if it was stored in clean containers. </p> <p>Rainwater is a “homogeneous mixture” or “solution.” The word “homogeneous” is derived from the Greek roots <em>homos</em> (meaning the same) and <em>genos</em> (meaning kind). When you look at rainwater, it looks the same throughout but dissolved gases from the <mark class="term" data-term="atmosphere" data-term-def="The collective mass of gases that surrounds the Earth or another planet." data-term-url="/en/glossary/view/atmosphere/8529">atmosphere</mark> are mixed in. The atmospheric gases are uniformly mixed or evenly distributed in the water, so rainwater is a <mark class="term" data-term="solution" data-term-def="A mixture of more than one substance with properties that do not vary within the sample. Commonly used to describe a&hellip;" data-term-url="/en/glossary/view/solution/1571">solution</mark>. </p> <p>Ancient Egyptians also collected water from the Nile River. The river water was a “heterogeneous mixture,” meaning you could see <mark class="term" data-term="sediment" data-term-def="Loose, unconsolidated material of the following compositions: <br> 1. rock fragments (also called clasts) transported by wind, moving water,&hellip;" data-term-url="/en/glossary/view/sediment/3310">sediments</mark> and tiny <mark class="term" data-term="organism" data-term-def="Any connected living system, such as an animal, plant, fungus, or bacterium. Organisms may be composed of a single cell or&hellip;" data-term-url="/en/glossary/view/organism/2171">organisms</mark> mixed in the water. The word “heterogeneous” is derived from the Greek roots <em>heteros</em> (meaning different) and <em>genos</em> (meaning kind). </p> <p>The ancient Egyptians could see that the Nile River’s water was unclean. They were the first to add the chemical alum, a naturally occurring <mark class="term" data-term="mineral" data-term-def="A naturally formed, inorganic solid with a specific chemical composition and characteristic crystal structure. Examples of minerals include quartz (SiO<sub>2</sub>), salt&hellip;" data-term-url="/en/glossary/view/mineral/2978">mineral</mark>, to river water because they found that it caused <mark class="term" data-term="particle" data-term-def="A tiny piece of matter." data-term-url="/en/glossary/view/particle/8259">particles</mark> to settle at the bottom of the water container. Ancient Egyptians used the cleaner water at the top of the container and discarded the settled <mark class="term" data-term="matter" data-term-def="The substance that makes up physical objects." data-term-url="/en/glossary/view/matter/8264">matter</mark> at the bottom of the container. </p> <p>The ancient Egyptians also used ceramic filters to clean the river water. They added herbs, seeds, and stones to improve the water quality and taste. Other ancient cultures used <mark class="term" data-term="method" data-term-def="A procedure or process; a systematic way of performing a task or conducting research." data-term-url="/en/glossary/view/method/8238">methods</mark> such as gravel filters, sand filters, and boiling to improve water quality. Regardless of the method, these examples show how river water (a heterogeneous mixture) could be physically separated to provide cleaner water for humans.</p> <div class="comprehension-checkpoint margin-y-4"> <h6 class="comprehension-checkpoint__header"> <span> <span class="icon icon-question"></span> </span> Comprehension Checkpoint </h6> <form class="" name="cc12517"> <div class="form-entry"> <div class="form-entry__field"> <span class="form-entry__field__label">The term “heterogeneous” refers to rainwater because it is a mixture of water and dissolved gases. </span> <div class="form-entry__option"> <div class="form-entry__option__radio" data-answer="correct"> <label> <input id="q1-12517-0-option-a" name="quiz-option-12517" type="radio" value="True" > <span class="option__label"> <span class="screen-reader-only">a.</span> True </span> </label> <span class="quiz__response" id="response-12517-0"> <strong>Correct!</strong> </span> </div> <div class="form-entry__option__radio" data-answer="incorrect"> <label> <input id="q1-12517-1-option-b" name="quiz-option-12517" type="radio" value="False" > <span class="option__label"> <span class="screen-reader-only">b.</span> False </span> </label> <span class="quiz__response" id="response-12517-1"> <strong>Incorrect.</strong> </span> </div> </div> </div> </div> </form> </div> </section> <section id="toc_3"> <h2>The history of water disinfection</h2><p>Ancient civilizations focused on physically separating water from the other <mark class="term" data-term="particle" data-term-def="A tiny piece of matter." data-term-url="/en/glossary/view/particle/8259">particles</mark> they could see in the <mark class="term" data-term="heterogeneous mixture" data-term-def="A mixture of two or more substances that can be easily separated by common physical means (i.e., settling, filtration, etc.).&hellip;" data-term-url="/en/glossary/view/heterogeneous+mixture/1567">heterogeneous mixture</mark>. What was not seen were the disease-causing <mark class="term" data-term="organism" data-term-def="Any connected living system, such as an animal, plant, fungus, or bacterium. Organisms may be composed of a single cell or&hellip;" data-term-url="/en/glossary/view/organism/2171">organisms</mark> from animal waste or other sources that can contaminate water. But the causes of these diseases were unknown in ancient times. In fact, many people believed that diseases were caused by humans upsetting the gods. </p> <p>The disinfection of water began centuries later after a cholera <mark class="term" data-term="outbreak" data-term-def="A sudden eruption or rise in the occurrence of a particular disease within a population or geographic area." data-term-url="/en/glossary/view/outbreak/8746">outbreak</mark> in London in 1854. Cholera is an intestinal disease caused by <mark class="term" data-term="bacteria" data-term-def="(plural of bacterium) A large group of one-celled organisms that are found almost everywhere." data-term-url="/en/glossary/view/bacteria/8679">bacteria</mark> that leads to vomiting and diarrhea. In the mid-1800s, Dr. John Snow, a British medical doctor, mapped the location of each cholera death in the Soho area of London to look for a pattern, as shown in Figure 4.</p> <div class="figure"> <figure> <button class="lightbox-button lightbox-button--icon" data-lightbox=""> <img src="/img/library/modules/mid280/Image/VLObject-12519-22081902080715.png" alt="Figure 4: A representation of the 1854 map of cholera deaths by Snow. The map revealed a pattern of cases occurring near the Broad Street water pump, as shown in red." /> </button> <figcaption> <p><strong>Figure 4:</strong> A representation of the 1854 map of cholera deaths by Snow. The map revealed a pattern of cases occurring near the Broad Street water pump, as shown in red.</p> <span class="credit">image ©Public Domain</span> </figcaption> </figure> </div> <p>At the time, indoor plumbing was rare. Instead, most people used one of several central pumping stations to get their water or wash household items. By mapping the locations of cholera deaths, Snow discovered something interesting—many of the people who developed cholera lived near and used London’s Broad Street pump. </p> <p>Snow studied the conditions at the Broad Street pump. He learned that many residents washed their clothes near the pump since it was their only water source. One resident, a mother whose baby suffered from cholera, washed contaminated diapers three feet from the pump. Snow realized the contaminated wash water could leak into the water supply. </p> <p>Snow appealed to the local governing body, the Board of Guardians, who took action by preventing residents from accessing the Broad Street water supply. With access to the Broad Street pump closed, the number of cholera cases in the city declined quickly. Snow had used his maps, a form of a scientific <mark class="term" data-term="model" data-term-def="A representation, pattern, or mathematical description that can help scientists replicate a system." data-term-url="/en/glossary/view/model/8236">model</mark>, to understand London’s cholera <mark class="term" data-term="outbreak" data-term-def="A sudden eruption or rise in the occurrence of a particular disease within a population or geographic area." data-term-url="/en/glossary/view/outbreak/8746">outbreak</mark> and take action to <mark class="term" data-term="control" data-term-def="In science, a control is a system for which the expected change or outcome is well known and is measured or&hellip;" data-term-url="/en/glossary/view/control/3801">control</mark> it. By the late 1800s, the British took advantage of another scientific discovery—that chloride <mark class="term" data-term="ion" data-term-def="An atom or molecule that has acquired an electrical charge by either gaining or losing electrons. A cation is an ion&hellip;" data-term-url="/en/glossary/view/ion/853">ions</mark> could be used to control outbreaks of infectious diseases. The British began adding <mark class="term" data-term="compound" data-term-def="A material formed by the chemical combination of elements in defined proportions. Compounds can be chemically decomposed into simpler substances." data-term-url="/en/glossary/view/compound/1517">compounds</mark> with chloride <mark class="term" data-term="ion" data-term-url="/en/glossary/view/ion" data-term-def="An atom or molecule that has acquired an electrical charge by either gaining or losing electrons. A cation is an ion&hellip;">ions</mark> to drinking water to kill the <mark class="term" data-term="bacteria" data-term-def="(plural of bacterium) A large group of one-celled organisms that are found almost everywhere." data-term-url="/en/glossary/view/bacteria/8679">bacteria</mark> that caused cholera and other diseases. </p> <p>The practice of disinfecting water supplies with chloride ions began in the United States shortly after that. Over time, <mark class="term" data-term="treatment" data-term-def="In science, a treatment refers to a method for fixing or manipulating an independent variable in the course of scientific research.&hellip;" data-term-url="/en/glossary/view/treatment/3799">treatment</mark> <mark class="term" data-term="method" data-term-def="A procedure or process; a systematic way of performing a task or conducting research." data-term-url="/en/glossary/view/method/8238">methods</mark> and technologies have improved. Today our water supply is constantly monitored to ensure it is safe for human consumption. The <mark class="term" data-term="Environmental Protection Agency" data-term-def="An independent federal agency of the United States government established to coordinate programs to reduce pollution and protect the environment." data-term-url="/en/glossary/view/Environmental+Protection+Agency/3900">Environmental Protection Agency</mark> (EPA) sets national standards for safe drinking water in the United States.  </p> <p>How can you find out if the tap water you drink is safe? Communities release consumer confidence reports annually explaining the substances in the water supply. You can find information from your local community about what substances might be present in the homogeneous <mark class="term" data-term="solution" data-term-def="A mixture of more than one substance with properties that do not vary within the sample. Commonly used to describe a&hellip;" data-term-url="/en/glossary/view/solution/1571">solution</mark> that is your tap water. While water testing has made our drinking water much cleaner and safer than in the 1800s, there are occasional breakdowns in the <mark class="term" data-term="system" data-term-def="A group of interacting, interrelated or interdependent components that form a complex whole. The size of the system is defined for&hellip;" data-term-url="/en/glossary/view/system/3904">system</mark>, as infamously happened in Flint, Michigan, in the mid-2010s. </p> <div class="comprehension-checkpoint margin-y-4"> <h6 class="comprehension-checkpoint__header"> <span> <span class="icon icon-question"></span> </span> Comprehension Checkpoint </h6> <form class="" name="cc12521"> <div class="form-entry"> <div class="form-entry__field"> <span class="form-entry__field__label">What did the British add to their drinking water to kill harmful bacteria that cause cholera and other diseases?</span> <div class="form-entry__option"> <div class="form-entry__option__radio" data-answer="correct"> <label> <input id="q1-12521-0-option-a" name="quiz-option-12521" type="radio" value="Chloride ions" > <span class="option__label"> <span class="screen-reader-only">a.</span> Chloride ions </span> </label> <span class="quiz__response" id="response-12521-0"> <strong>Correct!</strong> </span> </div> <div class="form-entry__option__radio" data-answer="incorrect"> <label> <input id="q1-12521-1-option-b" name="quiz-option-12521" type="radio" value="Salt" > <span class="option__label"> <span class="screen-reader-only">b.</span> Salt </span> </label> <span class="quiz__response" id="response-12521-1"> <strong>Incorrect.</strong> </span> </div> </div> </div> </div> </form> </div> </section> <section id="toc_4"> <h2>Water crisis in Flint, Michigan</h2><p>Dr. Mona Hanna-Attisha knows all too well what can happen if governments do not take on the responsibility of treating drinking water. Hanna-Attisha immigrated to the United States as a child refugee from Iraq. She received college <mark class="term" data-term="degree" data-term-def="[<strong>temperature</strong>] One graduated unit of measure on a Fahrenheit or Celsius temperature scale. On the Kelvin scale, graduations are called Kelvins. <br> <br> [<strong>geometry</strong>]&hellip;" data-term-url="/en/glossary/view/degree/8535">degrees</mark> in environmental studies, sustainability, and public health before attending medical school. In 2015, Hanna-Attisha was practicing pediatrics in Flint, Michigan, when she visited an old high school friend after <mark class="term" data-term="work" data-term-def="A process that occurs when a force acts over a distance, as when an object is moved. Work equals the multiple&hellip;" data-term-url="/en/glossary/view/work/1502">work</mark> one day. She learned from her friend, a water quality expert, that the water in Flint was not being treated properly and probably contained lead. Hanna-Attisha was alarmed.</p> <p>She knew that the city water supply had changed over the previous year and a half to save money. Rather than receiving treated water from Detroit, water from the Flint River was pumped to a water <mark class="term" data-term="treatment" data-term-def="In science, a treatment refers to a method for fixing or manipulating an independent variable in the course of scientific research.&hellip;" data-term-url="/en/glossary/view/treatment/3799">treatment</mark> plant to provide tap water for residents. However, what was unknown was that the water was not treated correctly—the treatment did not account for the old pipes in the city’s infrastructure made of iron, copper, and lead. High levels of chloride <mark class="term" data-term="ion" data-term-def="An atom or molecule that has acquired an electrical charge by either gaining or losing electrons. A cation is an ion&hellip;" data-term-url="/en/glossary/view/ion/853">ions</mark> were added to kill pathogens in the river water. However, the high levels of chloride <mark class="term" data-term="ion" data-term-url="/en/glossary/view/ion" data-term-def="An atom or molecule that has acquired an electrical charge by either gaining or losing electrons. A cation is an ion&hellip;">ions</mark> also caused lead from the pipes to dissolve into the water forming an invisible <mark class="term" data-term="solution" data-term-def="A mixture of more than one substance with properties that do not vary within the sample. Commonly used to describe a&hellip;" data-term-url="/en/glossary/view/solution/1571">solution</mark>. </p> <p>Hanna-Attisha knew that children exposed to lead might physically and behaviorally be affected. The exposure could impair children's nervous <mark class="term" data-term="system" data-term-def="A group of interacting, interrelated or interdependent components that form a complex whole. The size of the system is defined for&hellip;" data-term-url="/en/glossary/view/system/3904">systems</mark>, hearing, growth, and blood <mark class="term" data-term="cell" data-term-def="The basic structural unit of all living things." data-term-url="/en/glossary/view/cell/8286">cell</mark> function and formation. Further, exposed children may have learning problems, including hyperactivity. </p> <p>Hanna-Attisha knew that she needed <mark class="term" data-term="data" data-term-def="(plural form of <b>datum</b>) A collection of pieces of information, generally taking the form of numbers, text, bits, or facts, that&hellip;" data-term-url="/en/glossary/view/data/3729">data</mark> to immediately sound the alarm on the presence of high levels of lead in the tap water. So, she looked at medical <mark class="term" data-term="record" data-term-def="A written account or description. <br> <b>[verb]</b> To write an account or description." data-term-url="/en/glossary/view/record/8239">records</mark> to see if blood lead levels in children across the city had changed since the shift in the water supply. What she found was alarming: Blood lead levels had doubled and even tripled for some children. </p> <p>Hanna-Attisha knew that publishing her findings would take months for <mark class="term" data-term="peer review" data-term-def="The process of subjecting scholarly work, research or ideas to the scrutiny of others who are experts in the same field&hellip;" data-term-url="/en/glossary/view/peer+review/4761">peer review</mark>, but this problem was immediate. So, because of her concern for children’s health, Hanna-Attisha risked her career by publicly announcing her findings in 2015 before publishing them. Although she initially faced criticism, ultimately, she was praised for exposing the Flint water crisis. Figure 5 shows the results of Dr. Hanna-Attisha’s study that was published in 2016 (Hanna-Attisha et al. 2016). This bar graph shows the percent of children with elevated blood lead levels outside of Flint (left) and in Flint (right). The blue bars show the percentages before the change in the water source, and the red bars show the percentages after. The percentage of children with elevated blood lead levels increased significantly in all of Flint after the change in the water source.</p> <div class="figure"> <figure> <button class="lightbox-button lightbox-button--icon" data-lightbox=""> <img src="/img/library/modules/mid280/Image/VLObject-12523-22081902081324.png" alt="Figure 5: A bar graph showing the results of Hanna-Attisha’s study. The graph shows that a higher percentage of children in the city of Flint, Michigan had elevated blood lead levels compared to those who lived outside of Flint." /> </button> <figcaption> <p><strong>Figure 5:</strong> A bar graph showing the results of Hanna-Attisha’s study. The graph shows that a higher percentage of children in the city of Flint, Michigan had elevated blood lead levels compared to those who lived outside of Flint.</p> <span class="credit">image ©<a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4985856/"> data from Hanna-Attisha et al. 2016</a> </span> </figcaption> </figure> </div> <p>Although residents had previously complained of the bad taste and smell of the water, city officials ignored the complaints. High levels of E. coli, an <mark class="term" data-term="indicator" data-term-def="A substance that, when added to an aqueous solution, has a color determined by the pH. If reactant is added&hellip;" data-term-url="/en/glossary/view/indicator/12228">indicator</mark> of animal or sewage waste contamination, had even prompted a boil-water order several months after the shift in the water supply. Still, the city did not change its supply. The third-largest <mark class="term" data-term="outbreak" data-term-def="A sudden eruption or rise in the occurrence of a particular disease within a population or geographic area." data-term-url="/en/glossary/view/outbreak/8746">outbreak</mark> of Legionnaires disease in U.S. history occurred in 2015 because of the tainted water supply, killing 12 people and causing more than 87 people to report being ill.</p> <p>In Flint, Michigan, government safeguards had failed. Part of the problem was that the city overlooked many complaints because of the demographics. Nearly 41% of the city’s <mark class="term" data-term="population" data-term-def="In biology, the population is all individuals of a certain kind of plant or animal that live in a particular habitat.&hellip;" data-term-url="/en/glossary/view/population/8283">population</mark> lived below the poverty line. Demographically, about 57% of the population was Black, 37% white, 4% Latino, and 4% mixed race. </p> <p>Advocates for the victims say that the citizens of Flint experienced environmental racism. These events, and Hanna-Attisha’s <mark class="term" data-term="research" data-term-def="A study or an investigation." data-term-url="/en/glossary/view/research/8257">research</mark>, led to a <mark class="term" data-term="group" data-term-def="A column of elements in the periodic table." data-term-url="/en/glossary/view/group/8566">group</mark> of citizens and activists suing the city and state. As a result, the city gave bottled water to residents, improved water testing significantly, and eventually replaced lead-containing pipes. </p> <div class="comprehension-checkpoint margin-y-4"> <h6 class="comprehension-checkpoint__header"> <span> <span class="icon icon-question"></span> </span> Comprehension Checkpoint </h6> <form class="" name="cc12525"> <div class="form-entry"> <div class="form-entry__field"> <span class="form-entry__field__label">How did they identify lead in Flint drinking water?</span> <div class="form-entry__option"> <div class="form-entry__option__radio" data-answer="incorrect"> <label> <input id="q1-12525-0-option-a" name="quiz-option-12525" type="radio" value="The water smelled bad." > <span class="option__label"> <span class="screen-reader-only">a.</span> The water smelled bad. </span> </label> <span class="quiz__response" id="response-12525-0"> <strong>Incorrect.</strong> </span> </div> <div class="form-entry__option__radio" data-answer="correct"> <label> <input id="q1-12525-1-option-b" name="quiz-option-12525" type="radio" value="High levels of lead were found in children’s blood." > <span class="option__label"> <span class="screen-reader-only">b.</span> High levels of lead were found in children’s blood. </span> </label> <span class="quiz__response" id="response-12525-1"> <strong>Correct!</strong> </span> </div> </div> </div> </div> </form> </div> </section> <section id="toc_5"> <h2>Classification of substances</h2><p>Let’s take what you have learned about water as a substance and use it to build a <mark class="term" data-term="model" data-term-def="A representation, pattern, or mathematical description that can help scientists replicate a system." data-term-url="/en/glossary/view/model/8236">model</mark> for the <mark class="term" data-term="classification" data-term-def="In biology, the arranging of groups of organisms into sets or divisions on the basis of their evolutionary relationships." data-term-url="/en/glossary/view/classification/879">classification</mark> of substances. The terms and examples you learned about water as a substance are used in the model.</p> <div class="figure"> <figure> <button class="lightbox-button lightbox-button--icon" data-lightbox=""> <img src="/img/library/modules/mid280/Image/VLObject-12527-22081902081656.png" alt="Figure 6: This is the classification system used by scientists to describe substances. The system categorizes substances as either pure substances, which are made up of a single type of element or compound, or mixtures of more than one." /> </button> <figcaption> <p><strong>Figure 6:</strong> This is the classification system used by scientists to describe substances. The system categorizes substances as either pure substances, which are made up of a single type of element or compound, or mixtures of more than one.</p> </figcaption> </figure> </div> <p>Figure 6 shows a <mark class="term" data-term="classification" data-term-def="In biology, the arranging of groups of organisms into sets or divisions on the basis of their evolutionary relationships." data-term-url="/en/glossary/view/classification/879">classification</mark> <mark class="term" data-term="system" data-term-def="A group of interacting, interrelated or interdependent components that form a complex whole. The size of the system is defined for&hellip;" data-term-url="/en/glossary/view/system/3904">system</mark> that most scientists use to describe substances as pure or <mark class="term" data-term="mixtures" data-term-def="two or more pure substances combined that retain their unique properties. Mixtures include homogeneous mixtures, also called or solutions, where one&hellip;" data-term-url="/en/glossary/view/mixtures/12622">mixtures</mark>. <mark class="term" data-term="pure substances" data-term-def="matter with a definite composition and unique properties, including elements and compounds. For example, hydrogen and oxygen are elements but when&hellip;" data-term-url="/en/glossary/view/pure+substances/12621">Pure substances</mark> include <mark class="term" data-term="element" data-term-def="One of fewer than 118 pure chemical substances. An element is a substance composed of atoms with identical atomic number." data-term-url="/en/glossary/view/element/1510">elements</mark> made up of the same <mark class="term" data-term="atom" data-term-def="The smallest unit of an element that retains the chemical properties of the element. Atoms can exist alone or in&hellip;" data-term-url="/en/glossary/view/atom/1509">atoms</mark> and <mark class="term" data-term="compound" data-term-def="A material formed by the chemical combination of elements in defined proportions. Compounds can be chemically decomposed into simpler substances." data-term-url="/en/glossary/view/compound/1517">compounds</mark> made up of the same <mark class="term" data-term="molecule" data-term-def="A particle formed by the chemical bonding of two or more atoms. The molecule is the smallest particle of a&hellip;" data-term-url="/en/glossary/view/molecule/1518">molecules</mark>. Mixtures are either homogeneous or heterogeneous. They can be made up of atoms, molecules, or a combination of the two. </p> <p>Remember the description of water <mark class="term" data-term="treatment" data-term-def="In science, a treatment refers to a method for fixing or manipulating an independent variable in the course of scientific research.&hellip;" data-term-url="/en/glossary/view/treatment/3799">treatment</mark> in ancient Egypt? We learned that rainwater is a <mark class="term" data-term="homogeneous mixture" data-term-def="A mixture of two or more substances that cannot be easily separated by common physical means (i.e., settling, filtration, etc.). A&hellip;" data-term-url="/en/glossary/view/homogeneous+mixture/1566">homogeneous mixture</mark> (or solution). If you look at a sample of rainwater closely, it appears to look the same throughout, although there are gases dissolved within. River water is a <mark class="term" data-term="heterogeneous mixture" data-term-def="A mixture of two or more substances that can be easily separated by common physical means (i.e., settling, filtration, etc.).&hellip;" data-term-url="/en/glossary/view/heterogeneous+mixture/1567">heterogeneous mixture</mark>. If you look at a sample of river water closely, you will see <mark class="term" data-term="sediment" data-term-def="Loose, unconsolidated material of the following compositions: <br> 1. rock fragments (also called clasts) transported by wind, moving water,&hellip;" data-term-url="/en/glossary/view/sediment/3310">sediments</mark> and tiny <mark class="term" data-term="organism" data-term-def="Any connected living system, such as an animal, plant, fungus, or bacterium. Organisms may be composed of a single cell or&hellip;" data-term-url="/en/glossary/view/organism/2171">organisms</mark>. It does not look the same throughout. Both types of mixtures can be physically separated through <mark class="term" data-term="distillation" data-term-def="the physical process of purifying a liquid by evaporation and condensation. For example, saltwater can be distilled to separate salt molecules&hellip;" data-term-url="/en/glossary/view/distillation/12620">distillation</mark> or filtration, as described earlier.</p> <p>Let’s look at some of the substances you use daily and use the <mark class="term" data-term="model" data-term-def="A representation, pattern, or mathematical description that can help scientists replicate a system." data-term-url="/en/glossary/view/model/8236">model</mark> in Figure 6 to classify them. When you use <mark class="term" data-term="liquid" data-term-def="The state of matter characterized by its condensed nature and ability to flow. Unlike gases, molecules within a liquid often experience&hellip;" data-term-url="/en/glossary/view/liquid/8727">liquid</mark> soap in the shower, you use a mixture of water, detergent, oil, fragrance, and color compounds. It is most likely homogeneous because it is the same throughout the container. Toothpaste is fun because it can be either a homogeneous or heterogeneous mixture. Some toothpaste is the same throughout the container—often a chalky white color. These are homogeneous mixtures. However, some types of toothpaste have different colored stripes or sparkles running through the tube. In this case, they are heterogeneous mixtures because they look different throughout. Toothpaste contains fluoride, abrasives, flavoring, glycerol, and detergent compounds. </p> <p>What about breakfast foods and drinks? They are usually mixtures of compounds, elements, or a combination of both. For example, many breakfast cereals contain whole grains and compounds like <mark class="term" data-term="sugar" data-term-def="A water-soluble crystalline carbohydrate. There are many types of sugar of varying degrees of sweetness, including fructose, which occurs naturally in&hellip;" data-term-url="/en/glossary/view/sugar/5309">sugar</mark>, flavoring, vitamins, and <mark class="term" data-term="mineral" data-term-def="A naturally formed, inorganic solid with a specific chemical composition and characteristic crystal structure. Examples of minerals include quartz (SiO<sub>2</sub>), salt&hellip;" data-term-url="/en/glossary/view/mineral/2978">minerals</mark>. What is sugar by itself when sprinkled on your cereal? It is a compound or pure substance. If you have an <mark class="term" data-term="energy" data-term-def="An abstract property defined as the capacity to do work. The basic forms of energy include chemical, electrical, mechanical, nuclear, and&hellip;" data-term-url="/en/glossary/view/energy/1497">energy</mark> drink, you are having a homogeneous mixture or <mark class="term" data-term="solution" data-term-def="A mixture of more than one substance with properties that do not vary within the sample. Commonly used to describe a&hellip;" data-term-url="/en/glossary/view/solution/1571">solution</mark> of mostly the compounds water, sugar, and caffeine. However, the aluminum can that it comes in is a pure substance because aluminum is an element. And the coins you used to buy the drink from a vending machine? They are likely a mixture of copper and nickel—even <mark class="term" data-term="solid" data-term-def="A collection of atoms or molecules that are held together so that, under constant conditions, they maintain a defined shape and&hellip;" data-term-url="/en/glossary/view/solid/7571">solid</mark> substances can be mixtures. </p> <p>Let’s see if you recognize the classification of substances based on models. Look at Figure 7. </p> <div class="figure"> <figure> <button class="lightbox-button lightbox-button--icon" data-lightbox=""> <img src="/img/library/modules/mid280/Image/VLObject-12529-22081902081855.png" alt="Figure 7: Models of two different substances at the molecular level. How would you classify these substances?" /> </button> <figcaption> <p><strong>Figure 7:</strong> Models of two different substances at the molecular level. How would you classify these substances?</p> </figcaption> </figure> </div> <p>In Figure 7, the <mark class="term" data-term="model" data-term-def="A representation, pattern, or mathematical description that can help scientists replicate a system." data-term-url="/en/glossary/view/model/8236">model</mark> on the left includes <mark class="term" data-term="molecule" data-term-def="A particle formed by the chemical bonding of two or more atoms. The molecule is the smallest particle of a&hellip;" data-term-url="/en/glossary/view/molecule/1518">molecules</mark> that are all the same. This is a pure substance containing molecules of the same <mark class="term" data-term="compound" data-term-def="A material formed by the chemical combination of elements in defined proportions. Compounds can be chemically decomposed into simpler substances." data-term-url="/en/glossary/view/compound/1517">compound</mark>. What about the model on the right? There are molecules of two different compounds. One compound contains two <mark class="term" data-term="atom" data-term-def="The smallest unit of an element that retains the chemical properties of the element. Atoms can exist alone or in&hellip;" data-term-url="/en/glossary/view/atom/1509">atoms</mark> of different <mark class="term" data-term="element" data-term-def="One of fewer than 118 pure chemical substances. An element is a substance composed of atoms with identical atomic number." data-term-url="/en/glossary/view/element/1510">elements</mark>, represented by the blue and orange colors. The other compound has two atoms of the same element, as shown in green—a type of compound we call “diatomic.” We can’t tell whether this substance is heterogeneous or homogeneous on this <mark class="term" data-term="scale" data-term-def="An instrument for measuring heat energy or weight in which units are marked at intervals; a system for quantifying heat energy&hellip;" data-term-url="/en/glossary/view/scale/8536">scale</mark>. Sometimes it is difficult to classify a substance without more information. </p> <p>Pure substances can either be elements or compounds. Remember that compounds are chemically made and can be chemically separated; <mark class="term" data-term="mixtures" data-term-def="two or more pure substances combined that retain their unique properties. Mixtures include homogeneous mixtures, also called or solutions, where one&hellip;" data-term-url="/en/glossary/view/mixtures/12622">mixtures</mark> are physically mixed and can be physically separated. Let’s see if the properties of each substance can help.</p> <div class="comprehension-checkpoint margin-y-4"> <h6 class="comprehension-checkpoint__header"> <span> <span class="icon icon-question"></span> </span> Comprehension Checkpoint </h6> <form class="" name="cc12531"> <div class="form-entry"> <div class="form-entry__field"> <span class="form-entry__field__label">Mixtures may include different combinations of elements and compounds.</span> <div class="form-entry__option"> <div class="form-entry__option__radio" data-answer="incorrect"> <label> <input id="q1-12531-0-option-a" name="quiz-option-12531" type="radio" value="False" > <span class="option__label"> <span class="screen-reader-only">a.</span> False </span> </label> <span class="quiz__response" id="response-12531-0"> <strong>Incorrect.</strong> </span> </div> <div class="form-entry__option__radio" data-answer="correct"> <label> <input id="q1-12531-1-option-b" name="quiz-option-12531" type="radio" value="True" > <span class="option__label"> <span class="screen-reader-only">b.</span> True </span> </label> <span class="quiz__response" id="response-12531-1"> <strong>Correct!</strong> </span> </div> </div> </div> </div> </form> </div> <p>Pure substances have different characteristics than <mark class="term" data-term="mixtures" data-term-def="two or more pure substances combined that retain their unique properties. Mixtures include homogeneous mixtures, also called or solutions, where one&hellip;" data-term-url="/en/glossary/view/mixtures/12622">mixtures</mark>. Let’s learn what these characteristics are. Table 1 compares typical properties of <mark class="term" data-term="pure substances" data-term-def="matter with a definite composition and unique properties, including elements and compounds. For example, hydrogen and oxygen are elements but when&hellip;" data-term-url="/en/glossary/view/pure+substances/12621">pure substances</mark> and mixtures to help you recognize some patterns.</p> <div class="figure"> <figure> <button class="lightbox-button lightbox-button--icon" data-lightbox=""> <img src="/img/library/modules/mid280/Image/VLObject-12536-22081902083717.png" alt="Table 1: A comparison table of the properties of pure substances versus mixtures. What patterns do you see between pure substances and mixtures in the table?" /> </button> <figcaption> <p><strong>Table 1:</strong> A comparison table of the properties of pure substances versus mixtures. What patterns do you see between pure substances and mixtures in the table?</p> </figcaption> </figure> </div> </section> <section id="toc_6"> <h2>Properties of substances</h2><p>Pure substances are just that—pure. They are made up of a single type of <mark class="term" data-term="compound" data-term-def="A material formed by the chemical combination of elements in defined proportions. Compounds can be chemically decomposed into simpler substances." data-term-url="/en/glossary/view/compound/1517">compound</mark> or <mark class="term" data-term="element" data-term-def="One of fewer than 118 pure chemical substances. An element is a substance composed of atoms with identical atomic number." data-term-url="/en/glossary/view/element/1510">element</mark> and thus have a chemical <mark class="term" data-term="formula" data-term-def="An expression of the composition of a chemical compound using symbols." data-term-url="/en/glossary/view/formula/8554">formula</mark> defined by that compound or element. <mark class="term" data-term="pure substances" data-term-def="matter with a definite composition and unique properties, including elements and compounds. For example, hydrogen and oxygen are elements but when&hellip;" data-term-url="/en/glossary/view/pure+substances/12621">Pure substances</mark> cannot be separated into parts, except in the case of compounds, which can be chemically broken down into their elements.  </p> <p>Mixtures are combinations of two or more pure substances made by physical <mark class="term" data-term="mean" data-term-def="In statistics, mean commonly refers to the arithmetic mean, also called the average, which is one measure of the mid-point of&hellip;" data-term-url="/en/glossary/view/mean/4221">means</mark> (pouring them together, for example). They can be separated by physical means (like filtering), though sometimes this can take a lot of <mark class="term" data-term="work" data-term-def="A process that occurs when a force acts over a distance, as when an object is moved. Work equals the multiple&hellip;" data-term-url="/en/glossary/view/work/1502">work</mark>. <mark class="term" data-term="mixtures" data-term-def="two or more pure substances combined that retain their unique properties. Mixtures include homogeneous mixtures, also called or solutions, where one&hellip;" data-term-url="/en/glossary/view/mixtures/12622">Mixtures</mark> have no single chemical formulas because they do not have definite compositions—they are made up of different amounts of elements or compounds. </p> <p>For example, you may use a recipe to stir a chocolate chip cookie mixture, but the recipe varies according to individual tastes. You physically mix up chocolate chip cookies, but how could you physically separate them? Do you ever pick the chocolate chips out of the dough and eat them? The dough could also be separated by dissolving it, evaporating the water, and sorting the ingredients. The ingredients retain their unique properties in the dough. Chocolate chip cookie dough is a <mark class="term" data-term="heterogeneous mixture" data-term-def="A mixture of two or more substances that can be easily separated by common physical means (i.e., settling, filtration, etc.).&hellip;" data-term-url="/en/glossary/view/heterogeneous+mixture/1567">heterogeneous mixture</mark> because you can see the <mark class="term" data-term="particle" data-term-def="A tiny piece of matter." data-term-url="/en/glossary/view/particle/8259">particles</mark> that make it up.</p></section> <section id="toc_7"> <h2>Brief recap</h2><p>You have learned about many amazing substances that we use every day. In its purest form, water is a pure substance made up of only <mark class="term" data-term="molecule" data-term-def="A particle formed by the chemical bonding of two or more atoms. The molecule is the smallest particle of a&hellip;" data-term-url="/en/glossary/view/molecule/1518">molecules</mark> containing hydrogen and oxygen. But as this same water travels to your home, it becomes a mixture (or solution). As it goes through a local river or lake, the water picks up <mark class="term" data-term="particle" data-term-def="A tiny piece of matter." data-term-url="/en/glossary/view/particle/8259">particles</mark> and <mark class="term" data-term="organism" data-term-def="Any connected living system, such as an animal, plant, fungus, or bacterium. Organisms may be composed of a single cell or&hellip;" data-term-url="/en/glossary/view/organism/2171">organisms</mark> that make it a <mark class="term" data-term="heterogeneous mixture" data-term-def="A mixture of two or more substances that can be easily separated by common physical means (i.e., settling, filtration, etc.).&hellip;" data-term-url="/en/glossary/view/heterogeneous+mixture/1567">heterogeneous mixture</mark>. That heterogeneous mixture is physically separated by filtration at a water <mark class="term" data-term="treatment" data-term-def="In science, a treatment refers to a method for fixing or manipulating an independent variable in the course of scientific research.&hellip;" data-term-url="/en/glossary/view/treatment/3799">treatment</mark> plant. Then it is mixed with chloride and fluoride <mark class="term" data-term="ion" data-term-def="An atom or molecule that has acquired an electrical charge by either gaining or losing electrons. A cation is an ion&hellip;" data-term-url="/en/glossary/view/ion/853">ions</mark>, forming a <mark class="term" data-term="homogeneous mixture" data-term-def="A mixture of two or more substances that cannot be easily separated by common physical means (i.e., settling, filtration, etc.). A&hellip;" data-term-url="/en/glossary/view/homogeneous+mixture/1566">homogeneous mixture</mark> that comes out of our faucets and you can drink from a glass. <mark class="term" data-term="mixtures" data-term-def="two or more pure substances combined that retain their unique properties. Mixtures include homogeneous mixtures, also called or solutions, where one&hellip;" data-term-url="/en/glossary/view/mixtures/12622">Mixtures</mark> and <mark class="term" data-term="pure substances" data-term-def="matter with a definite composition and unique properties, including elements and compounds. For example, hydrogen and oxygen are elements but when&hellip;" data-term-url="/en/glossary/view/pure+substances/12621">pure substances</mark> are all around us, and we depend on them for life!</p> </div> </section> <hr class="border-color-dark" /> <footer class="module__footer"> <p class="citation"> <em> Judi Luepke, PhD. “Substances” Visionlearning Vol. CHE-5 (3), 2022. </em> </p>  <div class="title-list" id="refs" name="refs"> <p class="h6 title-list__title"> References </p> <ul class="title-list__list"> <li>Hanna-Attisha, Mona, Jenny LaChance, Richard C. Sadler, and Allison C. Schnepp. "Elevated blood lead levels in children associated with the Flint drinking water crisis: a spatial analysis of risk and public health response." <em>American journal of public health</em> 106, no. 2 (2016): 283-290. https://doi.org/10.2105/AJPH.2015.303003</li> </ul> </div>  <div class="title-list" name="further"> <p class="h6 title-list__title"> Further Reading </p> <ul class="grid grid--column-2--md grid--column-3--md gap-1"> <li> <a class="no-hover-focus height-100" href="/en/library/Chemistry/1/Early-Ideas-about-Matter/49"> <article class="flex-row align-items-center flex-column--md align-items-start--md height-100 theme-light padding-2 gap-2"> <div class="width-30 width-auto--md"> <img class="border-radius box-shadow-1" src="/img/library/moduleImages/featured_image_49-23061209064421.jpeg" alt="Early Ideas about Matter"> </div> <div class="flex-grow-shrink"> <h2 class="h6 font-weight-normal"> Early Ideas about Matter: <em>From Democritus to Dalton</em> </h2> </div> </article> </a> </li> <li> <a class="no-hover-focus height-100" href="/en/library/Chemistry/1/Solutions-Solubility-and-Colligative-Properties/266"> <article class="flex-row align-items-center flex-column--md align-items-start--md height-100 theme-light padding-2 gap-2"> <div class="width-30 width-auto--md"> <img class="border-radius box-shadow-1" src="/img/library/moduleImages/featured_image_266-23061209064829.jpeg" alt="Solutions"> </div> <div class="flex-grow-shrink"> <h2 class="h6 font-weight-normal"> Solutions: <em>Molarity, solubility, and colligative properties</em> </h2> </div> </article> </a> </li> </ul> </div> </footer> </div>   </div>  <div class="order-1 order-2--lg module__tools"> <div class="narrow margin-x-auto position-sticky-top font-size-md"> <div class="padding-2 border-radius box-shadow-1--lg"> <div class="tabs" role="tablist"> <nav> <button class="button button--icon-label" id="tab-button-in-this-module" aria-label="Table of Contents" aria-controls="tab-panel-module__tools" aria-selected="true" role="tab"> <span class="icon icon-list" aria-hidden="true"></span> <span class="button__text">Contents</span> </button> <button class="button button--icon-label" id="tab-button-toggle-terms" aria-controls="tab-panel-toggle-terms" aria-selected="false" role="tab"> <span class="icon icon-glossary-highlight"></span> <span class="button__text">Glossary Terms</span> </button> </nav> <hr class="divider" /> <div class="tabs__panel shown" id="tab-panel-module__tools" aria-labelledby="tab-button-module__tools" role="tabpanel"> <p class="font-weight-bold margin-bottom-1"> Table of Contents </p> <div class="table-of-contents" id="module-toc"> <ul> <li><a href="/en/library/chemistry/1/substances/280#toc_1">Water as a substance</a> </li> <li><a href="/en/library/chemistry/1/substances/280#toc_2">Which water do we drink?</a> </li> <li><a href="/en/library/chemistry/1/substances/280#toc_3">The history of water disinfection</a> </li> <li><a href="/en/library/chemistry/1/substances/280#toc_4">Water crisis in Flint, Michigan</a> </li> <li><a href="/en/library/chemistry/1/substances/280#toc_5">Classification of substances</a> </li> <li><a href="/en/library/chemistry/1/substances/280#toc_6">Properties of substances</a> </li> <li><a href="/en/library/chemistry/1/substances/280#toc_7">Brief recap</a> </li> </ul> </div> </div>   <div class="tabs__panel" id="tab-panel-toggle-terms" aria-labelledby="tab-button-toggle-terms" role="tabpanel"> <div class="reading-toggle"> <div class="reading-toggle__switch"> <div class="form-entry__option__switch"> <label> <input type="checkbox" name="termsToggleSwitch" id="terms-toggle-switch" /> <span class="switch__slider"></span> <span class="option__label text-decoration-none font-size-md"> Highlight Glossary Terms </span> </label> </div> </div> <div class="reading-toggle__help"> <p> <em> Activate glossary term highlighting to easily identify key terms within the module. Once highlighted, you can click on these terms to view their definitions. </em> </p> </div> </div> </div> <div class="tabs__panel" id="tab-panel-toggle-ngss" aria-labelledby="tab-button-toggle-ngss" role="tabpanel"> <div class="reading-toggle"> <div class="reading-toggle__switch"> <div class="form-entry__option__switch"> <label> <input type="checkbox" name="ngssToggleSwitch" id="ngss-toggle-switch" /> <span class="switch__slider"></span> <span class="option__label text-decoration-none font-size-md"> Show NGSS Annotations </span> </label> </div> </div> <div class="reading-toggle__help"> <p> <em> Activate NGSS annotations to easily identify NGSS standards within the module. 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