{"id":4017,"date":"2026-05-21T07:04:50","date_gmt":"2026-05-21T06:04:50","guid":{"rendered":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/calculations-with-solutions-and-gases\/concentrations-in-ppm\/"},"modified":"2026-06-28T06:01:24","modified_gmt":"2026-06-28T05:01:24","slug":"concentrations-in-ppm","status":"publish","type":"page","link":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/calculations-with-solutions-and-gases\/concentrations-in-ppm\/","title":{"rendered":"Concentrations in PPM"},"content":{"rendered":"\n<!--\n===============================================================================\nONLINE LEARNING SYSTEM COPYRIGHT NOTICE\n\u00a9 Online Learning System. All rights reserved.\n\nThis WordPress revision page HTML, CSS, content sequence, educational wording,\nlayout structure, schema structure and embedded design logic are protected\nintellectual property of Online Learning System.\n\nUnauthorised copying, redistribution, resale, modification, republication,\nscraping, extraction, derivative reuse, automated harvesting or removal of\ncopyright notices is strictly prohibited.\n\nBackend copyright marker:\nOLS-T1-CONCENTRATIONS-IN-PPM-REVISION-PAGE-2026\n\nPage:\nConcentrations in PPM (parts per million)\nEdexcel International A Level Chemistry\nUnit 1: Structure, Bonding and Introduction to Organic Chemistry\nTopic 1: Formulae, Equations and Amount of Substance\nWCH11\/01\n\nCopyright enforcement notes:\n- The visible student page is a free OLS revision resource.\n- The backend HTML structure, CSS architecture, card sequencing, schema graph,\n  revision wording, responsive table behaviour and embedded learning pathway are\n  proprietary OLS production assets.\n- Do not remove this notice.\n===============================================================================\n-->\n\n<section class=\"ols-revision-page ols-ppm-page\" data-owner=\"Online Learning System\" data-copyright=\"\u00a9 Online Learning System. 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{\n        padding: 16px;\n      }\n\n      .ols-image-lightbox-inner {\n        width: 100%;\n        max-height: 88vh;\n      }\n\n      .ols-image-lightbox-img {\n        max-height: 88vh;\n        border-radius: 16px;\n      }\n\n      .ols-image-lightbox-close {\n        top: 10px;\n        right: 10px;\n        width: 42px;\n        height: 42px;\n        font-size: 26px;\n      }\n    }\n\n  <\/style>\n\n  <!--\n    OLS protected content block.\n    Page: Concentrations in PPM.\n    This content is authored for Online Learning System and must not be scraped,\n    cloned, republished, resold, reformatted into derivative notes, or reused in\n    competing resources without written permission.\n  -->\n\n  <div class=\"ols-revision-layout\">\n    <aside class=\"ols-sidebar\">\r\n  <div class=\"ols-sidebar-header\">\r\n    <h3>Revision Notes<\/h3>\r\n    <p>A Level Chemistry<\/p>\r\n  <\/div>\r\n\r\n  <div class=\"ols-topic-group\">\r\n    <h4>Topic 1 Formulae, Equations and Amount of Substance<\/h4>\r\n\r\n    <ul class=\"ols-topic-list\">\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/atoms-elements-and-molecules\/\">Atoms, Elements and Molecules<\/a>\r\n      <\/li>\r\n\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/equations-and-reaction-types\/\">Equations and Reaction Types<\/a>\r\n\r\n        <ul class=\"ols-subtopic-list\">\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/equations-and-reaction-types\/writing-chemical-equations\/\">Writing Chemical Equations<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/equations-and-reaction-types\/typical-reactions-of-acids\/\">Typical Reactions of Acids<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/equations-and-reaction-types\/ionic-equations\/\">Ionic Equations<\/a>\r\n          <\/li>\r\n        <\/ul>\r\n      <\/li>\r\n\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/mole-calculations\/\">Mole Calculations<\/a>\r\n\r\n        <ul class=\"ols-subtopic-list\">\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/mole-calculations\/comparing-masses-of-substances\/\">Comparing Masses of Substances<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/mole-calculations\/calculations-involving-moles\/\">Calculations involving Moles<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/mole-calculations\/calculations-using-reacting-masses\/\">Calculations using Reacting Masses<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/mole-calculations\/the-yield-of-a-reaction\/\">The Yield of a Reaction<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/mole-calculations\/atom-economy\/\">Atom Economy<\/a>\r\n          <\/li>\r\n        <\/ul>\r\n      <\/li>\r\n\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/empirical-and-molecular-formulae\/\">Empirical and Molecular Formulae<\/a>\r\n\r\n        <ul class=\"ols-subtopic-list\">\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/empirical-and-molecular-formulae\/empirical-formulae\/\">Empirical Formulae<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/empirical-and-molecular-formulae\/molecular-formulae\/\">Molecular Formulae<\/a>\r\n          <\/li>\r\n        <\/ul>\r\n      <\/li>\r\n\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/calculations-with-solutions-and-gases\/\">Calculations with Solutions and Gases<\/a>\r\n\r\n        <ul class=\"ols-subtopic-list\">\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/calculations-with-solutions-and-gases\/molar-volume-calculations\/\">Molar Volume Calculations<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/calculations-with-solutions-and-gases\/concentrations-of-solutions\/\">Concentrations of Solutions<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/calculations-with-solutions-and-gases\/concentrations-in-ppm\/\">Concentrations in PPM<\/a>\r\n          <\/li>\r\n        <\/ul>\r\n      <\/li>\r\n    <\/ul>\r\n  <\/div>\r\n\r\n  <div class=\"ols-topic-group\">\r\n    <h4>Next Topics<\/h4>\r\n\r\n    <ul class=\"ols-topic-list\">\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-2-atomic-structure-and-the-periodic-table\/\">Atomic Structure and The Periodic Table<\/a>\r\n      <\/li>\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-3-bonding-structure\/\">Bonding &amp; Structure<\/a>\r\n      <\/li>\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-4-organic-chemistry-and-alkanes\/\">Organic Chemistry &amp; Alkanes<\/a>\r\n      <\/li>\r\n    <\/ul>\r\n  <\/div>\r\n<\/aside>\r\n\r\n<script>\r\n(function() {\r\n  function normalisePath(path) {\r\n    return String(path || '')\r\n      .split('?')[0]\r\n      .split('#')[0]\r\n      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    <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/\">A Level Chemistry<\/a> \/\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/\">Edexcel International<\/a> \/\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/\">Topic 1 Formulae, Equations and Amount of Substance<\/a> \/\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/mole-calculations\/\">Amount of Substance<\/a> \/\n        <span>Concentrations in PPM<\/span>\n      <\/nav>\n\n      <header class=\"ols-title-card\">\n        <h1>Concentrations in PPM<\/h1>\n        <p class=\"ols-page-intro\">A focused revision guide to expressing and calculating concentrations in parts per million (ppm) for Edexcel International A Level Chemistry. This page covers the meaning of ppm, the formulae for solutions and for gases in air, and full worked examples for both contexts.<\/p>\n\n        <div class=\"ols-badges\">\n          <div class=\"ols-badge\">Unit 1: Structure, Bonding and Introduction to Organic Chemistry<\/div>\n          <div class=\"ols-badge\">Topic 1: Formulae, Equations and Amount of Substance<\/div>\n          <div class=\"ols-badge\">WCH11\/01<\/div>\n        <\/div>\n\n        <div class=\"ols-author\">\n          <img decoding=\"async\" class=\"ols-author-avatar-img\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/05\/Author-Profile.jpeg\" alt=\"Dr. Mohammed Al-Fatah\">\n          <div class=\"ols-author-content\">\n            <h2 class=\"ols-author-title\">Written by:<br><span>Dr. Mohammed Al-Fatah<\/span><\/h2>\n            <p class=\"ols-author-description\">Chemistry specialist revision notes for A Level Chemistry.<\/p>\n            <a class=\"ols-linkedin-pill\" href=\"https:\/\/www.linkedin.com\/in\/doctormohammedfatah\/\" target=\"_blank\" rel=\"noopener noreferrer\">\n              <svg class=\"ols-linkedin-icon\" viewBox=\"0 0 24 24\" fill=\"currentColor\" aria-hidden=\"true\"><path d=\"M4.98 3.5C4.98 4.88 3.86 6 2.48 6S0 4.88 0 3.5 1.12 1 2.48 1s2.5 1.12 2.5 2.5zM.5 8h4V24h-4V8zm7 0h3.8v2.2h.1c.5-.9 1.8-2.2 3.9-2.2 4.2 0 5 2.8 5 6.4V24h-4v-7.6c0-1.8 0-4.2-2.6-4.2s-3 2-3 4v7.8h-4V8z\"><\/path><\/svg>\n              View LinkedIn Profile\n            <\/a>\n          <\/div>\n        <\/div>\n      <\/header>\n\n      <!-- Card 1: What is PPM -->\n      <article class=\"ols-note-card soft\">\n        <div class=\"ols-note-title\"><div class=\"ols-note-icon\">1<\/div><h2>What Does Parts Per Million (ppm) Mean?<\/h2><\/div>\n        <p>Concentrations of solutions can also be compared using the term <strong>parts per million<\/strong>, or <strong>ppm<\/strong>. This unit is often used for very low concentrations, such as pollutants in water or trace gases in the atmosphere.<\/p>\n        <p>The logic is simple. Think of the word &#8220;percent&#8221;; the &#8220;cent&#8221; part refers to 100, so 50% means 50 out of 100. <strong>Parts per million means out of a million.<\/strong> So 50 ppm means 50 parts out of 1 000 000 parts.<\/p>\n        <p>The &#8220;parts&#8221; usually refer to mass for solutions, or volume for gases. The parts can be measured in any unit of mass (or volume), but the unit must be the <strong>same on the top and the bottom<\/strong> of the fraction.<\/p>\n\n        <div class=\"ols-definition-box\">\n          <p><strong>Definition:<\/strong> ppm tells you how many parts of solute are present in one million parts of the total sample. For very dilute concentrations, ppm is more convenient than mol dm<sup>\u22123<\/sup>.<\/p>\n        <\/div>\n\n        <div class=\"ols-key-box\">\n          <p><strong>Useful equivalents:<\/strong> a concentration of 1 ppm means 1 g of solute in 1 000 000 g of solvent, or 1 mg in 1 000 000 mg. Grams and milligrams are the most commonly used units for solutions.<\/p>\n        <\/div>\n      <\/article>\n\n      <!-- Image 1: Understanding parts per million (introduction visual) -->\n      <div class=\"ols-zoom-card\">\n        <div class=\"ols-zoom-card-image\">\n          <img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/05\/Understanding-ppm.webp\" alt=\"Understanding parts per million (ppm) with a worked chemistry example for solution concentration\" class=\"ols-zoomable-img ols-lightbox-target\" draggable=\"false\">\n        <\/div>\n        <div class=\"ols-zoom-card-caption\">\n          <p>Because the units cancel inside the fraction, ppm is dimensionless; the value itself carries the meaning regardless of whether the masses are in g or mg.<\/p>\n        <\/div>\n      <\/div>\n\n      <!-- Card 2: Calculations for Solutions in PPM -->\n      <article class=\"ols-note-card\">\n        <div class=\"ols-note-title\"><div class=\"ols-note-icon\">2<\/div><h2>Calculations for Solutions in ppm<\/h2><\/div>\n        <p>For a solute dissolved in a solvent, the ppm formula uses masses:<\/p>\n\n        <div class=\"ols-equation-box\">\n          <strong>Concentration in ppm<\/strong> = (mass of solute \u00d7 1 000 000) \u00f7 mass of solvent\n        <\/div>\n\n        <p>The masses can be in any units, but they must be the <strong>same units<\/strong> on the top and the bottom. If they are given in different units, convert one of them before substituting.<\/p>\n\n        <div class=\"ols-worked-example\">\n          <h3>Example A \u2014 Solute in solvent<\/h3>\n          <p>A solution contains <strong>0.176 g of solute<\/strong> dissolved in <strong>750 g of solvent<\/strong>. What is the concentration in ppm?<\/p>\n          <p>The units of solute and solvent are already the same (both in grams), so the values can be directly inserted into the expression.<\/p>\n          <div class=\"ols-calc-row\">\n            <div class=\"ols-calc-cell\"><span>Mass of solute<\/span>0.176 g<\/div>\n            <div class=\"ols-calc-cell\"><span>Mass of solvent<\/span>750 g<\/div>\n            <div class=\"ols-calc-cell\"><span>Concentration in ppm<\/span>(0.176 \u00d7 1 000 000) \u00f7 750 = <strong>235 ppm<\/strong><\/div>\n          <\/div>\n        <\/div>\n\n        <div class=\"ols-key-box\">\n          <p><strong>Watch the units:<\/strong> if the question gives the solute in mg and the solvent in g, convert one of them so they match. Either change the solute to g (divide by 1000) or the solvent to mg (multiply by 1000) before substituting.<\/p>\n        <\/div>\n      <\/article>\n\n      <!-- Image 2: PPM calculations practical examples (worked examples support) -->\n      <div class=\"ols-zoom-card\">\n        <div class=\"ols-zoom-card-image\">\n          <img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/05\/PPM-calculations-practical-examples-guide.webp\" alt=\"Worked ppm calculations for practical examples in chemistry solutions and pollutants\" class=\"ols-zoomable-img ols-lightbox-target\" draggable=\"false\">\n        <\/div>\n        <div class=\"ols-zoom-card-caption\">\n          <p>The multiplication by 1 000 000 is what shifts a tiny mass ratio into a value that can be quoted as a whole number, which is why ppm is the standard way to report trace pollutants.<\/p>\n        <\/div>\n      <\/div>\n\n      <!-- Card 3: PPM for Gases in Air -->\n      <article class=\"ols-note-card purple\">\n        <div class=\"ols-note-title\"><div class=\"ols-note-icon\">3<\/div><h2>Calculations for Gases in ppm<\/h2><\/div>\n        <p>For gases in air, the ppm formula uses <strong>volumes<\/strong> rather than masses, because gas concentrations are most easily measured by volume.<\/p>\n\n        <div class=\"ols-equation-box\">\n          <strong>Concentration in ppm<\/strong> = (volume of gas \u00d7 1 000 000) \u00f7 volume of air\n        <\/div>\n\n        <p>The volumes can be in any unit (dm<sup>3<\/sup>, cm<sup>3<\/sup>, m<sup>3<\/sup>), but they must be the same on the top and the bottom of the fraction.<\/p>\n\n        <div class=\"ols-worked-example\">\n          <h3>Example B \u2014 Finding the volume of a trace gas<\/h3>\n          <p><strong>5000 dm<sup>3<\/sup> of air<\/strong> is found to contain ozone with a concentration of <strong>87 ppm<\/strong>. What volume of ozone is in this sample of air?<\/p>\n          <p>Rearrange the expression to make the volume of gas the subject:<\/p>\n          <p><strong>Volume of gas<\/strong> = (concentration in ppm \u00d7 volume of air) \u00f7 1 000 000<\/p>\n          <div class=\"ols-calc-row\">\n            <div class=\"ols-calc-cell\"><span>Concentration in ppm<\/span>87 ppm<\/div>\n            <div class=\"ols-calc-cell\"><span>Volume of air<\/span>5000 dm<sup>3<\/sup><\/div>\n            <div class=\"ols-calc-cell\"><span>Volume of ozone<\/span>(87 \u00d7 5000) \u00f7 1 000 000 = <strong>0.435 dm<sup>3<\/sup><\/strong><\/div>\n          <\/div>\n        <\/div>\n\n        <div class=\"ols-key-box\">\n          <p><strong>Learning tip:<\/strong> for ppm calculations with solutions, use the expression involving <strong>masses<\/strong>. For ppm calculations with gases, use the expression involving <strong>volumes<\/strong>. Mixing the two is a common error.<\/p>\n        <\/div>\n      <\/article>\n\n      <!-- Image 3: Atmospheric gases and ppm explained (gases context) -->\n      <div class=\"ols-zoom-card\">\n        <div class=\"ols-zoom-card-image\">\n          <img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/05\/Atmospheric-gases-and-ppm-explained.webp\" alt=\"Atmospheric gases and ppm explained including carbon dioxide trends and ppm calculations\" class=\"ols-zoomable-img ols-lightbox-target\" draggable=\"false\">\n        <\/div>\n        <div class=\"ols-zoom-card-caption\">\n          <p>Atmospheric carbon dioxide is reported in ppm precisely because its concentration in air is far too small to make mol dm<sup>\u22123<\/sup> a practical unit.<\/p>\n        <\/div>\n      <\/div>\n\n      <!-- Card 4: Comparing PPM Concentrations -->\n      <article class=\"ols-note-card orange\">\n        <div class=\"ols-note-title\"><div class=\"ols-note-icon\">4<\/div><h2>Comparing Two ppm Concentrations<\/h2><\/div>\n        <p>A common exam question asks you to compare two air samples and decide which has the higher concentration of a pollutant. The strategy is to calculate the ppm value for each sample using the same formula, then compare directly.<\/p>\n\n        <div class=\"ols-worked-example\">\n          <h3>Example C \u2014 Comparing two air samples for SO<sub>2<\/sub><\/h3>\n          <p>Two samples of air containing sulfur dioxide were analysed.<\/p>\n          <ul>\n            <li><strong>Sample 1:<\/strong> 500 dm<sup>3<\/sup> of air contained 37 cm<sup>3<\/sup> of sulfur dioxide.<\/li>\n            <li><strong>Sample 2:<\/strong> 4000 dm<sup>3<\/sup> of air contained 1.4 dm<sup>3<\/sup> of sulfur dioxide.<\/li>\n          <\/ul>\n          <p>Show, by calculation, which sample has the higher concentration of SO<sub>2<\/sub> in ppm.<\/p>\n\n          <p><strong>Sample 1:<\/strong> the volume of gas is in cm<sup>3<\/sup> and the volume of air is in dm<sup>3<\/sup>, so first convert 37 cm<sup>3<\/sup> to 0.037 dm<sup>3<\/sup> (or convert 500 dm<sup>3<\/sup> to 500 000 cm<sup>3<\/sup>; either works).<\/p>\n          <div class=\"ols-calc-row\">\n            <div class=\"ols-calc-cell\"><span>Sample 1<\/span>(0.037 \u00d7 1 000 000) \u00f7 500 = <strong>74 ppm<\/strong><\/div>\n            <div class=\"ols-calc-cell\"><span>Sample 2<\/span>(1.4 \u00d7 1 000 000) \u00f7 4000 = <strong>350 ppm<\/strong><\/div>\n            <div class=\"ols-calc-cell\"><span>Conclusion<\/span><strong>Sample 2 has the higher concentration of sulfur dioxide.<\/strong><\/div>\n          <\/div>\n        <\/div>\n\n        <div class=\"ols-key-box\">\n          <p><strong>Exam tip:<\/strong> always state the comparison conclusion in words after the calculation. If the question says &#8220;show, by calculation, which sample&#8230;&#8221;, you must do both the maths <em>and<\/em> the verbal statement to gain full marks.<\/p>\n        <\/div>\n      <\/article>\n\n      <!-- Card 5: Common Exam Points -->\n      <article class=\"ols-note-card soft\">\n        <div class=\"ols-note-title\"><div class=\"ols-note-icon\">5<\/div><h2>Common Exam Points<\/h2><\/div>\n        <ul>\n          <li>ppm stands for <strong>parts per million<\/strong>; it is a way of expressing <strong>very dilute concentrations<\/strong> as a whole number.<\/li>\n          <li>1 ppm means 1 part of solute in 1 000 000 parts of sample (for example, 1 g in 1 000 000 g, or 1 mg in 1 000 000 mg).<\/li>\n          <li>ppm is <strong>dimensionless<\/strong>: the units cancel inside the fraction, leaving a pure number.<\/li>\n          <li>For <strong>solutions<\/strong>: ppm = (mass of solute \u00d7 1 000 000) \u00f7 mass of solvent. Masses must be in the same unit.<\/li>\n          <li>For <strong>gases in air<\/strong>: ppm = (volume of gas \u00d7 1 000 000) \u00f7 volume of air. Volumes must be in the same unit.<\/li>\n          <li>When the units do not match, convert one of them <strong>before<\/strong> substituting (1 dm<sup>3<\/sup> = 1000 cm<sup>3<\/sup>; 1 g = 1000 mg).<\/li>\n          <li>The formula can be rearranged to find the volume (or mass) of solute when the ppm value is given.<\/li>\n          <li>For &#8220;show by calculation&#8221; questions, write both the working <em>and<\/em> a written comparison or conclusion.<\/li>\n          <li>Common real-world applications include atmospheric CO<sub>2<\/sub>, ozone, sulfur dioxide and trace metal pollutants in drinking water.<\/li>\n        <\/ul>\n      <\/article>\n\n      <!-- Check Your Understanding H5P 326 -->\n      <section class=\"ols-h5p-card\">\n        <h2>Check Your Understanding<\/h2>\n        <p>Use this activity to practise ppm calculations for both solutions and gases, including comparing sample concentrations.<\/p>\n        <div class=\"ols-h5p-grid\">\n          <div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-326\" class=\"h5p-iframe\" data-content-id=\"326\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Parts per Million Concentration Practice\"><\/iframe><\/div><\/div>\n        <\/div>\n      <\/section>\n\n      <!-- QuickSnap Summary -->\n      <section class=\"ols-quicksnap-card\">\n        <h2>QuickSnap<\/h2>\n        <p>This text summary condenses the page into the essential exam ideas.<\/p>\n        <ul class=\"ols-quicksnap-list\">\n          <li><strong>ppm:<\/strong> parts per million; how many parts of solute are present in 1 000 000 parts of sample.<\/li>\n          <li><strong>Solutions formula:<\/strong> ppm = (mass of solute \u00d7 1 000 000) \u00f7 mass of solvent.<\/li>\n          <li><strong>Gases formula:<\/strong> ppm = (volume of gas \u00d7 1 000 000) \u00f7 volume of air.<\/li>\n          <li><strong>Unit rule:<\/strong> mass units must match on the top and bottom for solutions; volume units must match for gases.<\/li>\n          <li><strong>Equivalents:<\/strong> 1 ppm = 1 g in 1 000 000 g = 1 mg in 1 000 000 mg.<\/li>\n          <li><strong>Rearranging:<\/strong> volume of gas = (ppm \u00d7 volume of air) \u00f7 1 000 000.<\/li>\n          <li><strong>Use case:<\/strong> ppm is preferred over mol dm<sup>\u22123<\/sup> for very dilute pollutants and atmospheric gases.<\/li>\n          <li><strong>Comparison questions:<\/strong> calculate ppm for each sample and state the conclusion in words.<\/li>\n        <\/ul>\n      <\/section>\n\n      <!-- Lightbox element -->\n      <div class=\"ols-image-lightbox\" id=\"olsImageLightboxPpm001\" aria-hidden=\"true\" role=\"dialog\" aria-modal=\"true\" aria-label=\"Expanded revision image\">\n        <div class=\"ols-image-lightbox-inner\">\n          <button class=\"ols-image-lightbox-close\" type=\"button\" aria-label=\"Close enlarged image\">\u00d7<\/button>\n          <img 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<div class=\"ols-course-cta-card\">\n\n    <div class=\"ols-course-cta-top\">\n\n      <a class=\"ols-course-cta-image-link\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/product\/formulae-equations-and-amount-of-substance-edexcel-t1\/\" aria-label=\"Open the Edexcel International A Level Chemistry Topic 1 Formulae, Equations and Amount of Substance course page\">\n        <div class=\"ols-course-cta-image\">\n          <img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/04\/edexcel-international-a-level-chemistry-topic-1-formulae-equations-amounts-of-substance-course-banner.jpg\" alt=\"Edexcel International A Level Chemistry Topic 1 Formulae, Equations and Amount of Substance course banner\">\n        <\/div>\n      <\/a>\n\n      <div class=\"ols-course-cta-content\">\n\n        <div class=\"ols-course-cta-header-row\">\n          <div class=\"ols-course-cta-kicker\">\n            Complete Topic 1 Formulae, Equations &amp; Amount of Substance Course\n          <\/div>\n          <a class=\"ols-course-button ols-course-button-top\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/product\/formulae-equations-and-amount-of-substance-edexcel-t1\/\">\n            View Course\n          <\/a>\n        <\/div>\n\n        <h2>Master Formulae, Equations and Amount of Substance for Edexcel International A Level Chemistry<\/h2>\n\n      <\/div>\n\n    <\/div>\n\n    <div class=\"ols-course-cta-intro-stats\">\n\n      <p class=\"ols-course-cta-intro\">\n        Continue from these free revision notes into the full Topic 1 Formulae, Equations and Amount of Substance course, with guided video teaching, diagnostic MCQ practice, teacher-marked short-answer questions and a specification assignment with a personalised progress report.\n      <\/p>\n\n      <div class=\"ols-course-cta-stats\">\n\n        <div class=\"ols-course-stat\">\n          <span>Guided learning<\/span>\n          <strong>Complete Topic 1<\/strong>\n        <\/div>\n\n        <div class=\"ols-course-stat\">\n          <span>Video lessons<\/span>\n          <strong>Full virtual lesson<\/strong>\n        <\/div>\n\n        <div class=\"ols-course-stat\">\n          <span>MCQ practice<\/span>\n          <strong>123 marks<\/strong>\n        <\/div>\n\n        <div class=\"ols-course-stat\">\n          <span>SAQ practice<\/span>\n          <strong>up to 145 marks<\/strong>\n        <\/div>\n\n      <\/div>\n\n    <\/div>\n\n    <div class=\"ols-course-cta-features\">\n\n      <div class=\"ols-course-feature\">\n        <h3>Guided video teaching<\/h3>\n        <p>Learn ppm calculations, concentrations of solutions, dilutions, molar volume calculations, the ideal gas equation, empirical formulae, mole calculations, percentage yield and atom economy through structured video lessons with worked examples and walkthroughs.<\/p>\n      <\/div>\n\n      <div class=\"ols-course-feature\">\n        <h3>Instant MCQ feedback<\/h3>\n        <p>Auto-marked MCQ quizzes provide immediate diagnostic feedback for every answer choice.<\/p>\n      <\/div>\n\n      <div class=\"ols-course-feature\">\n        <h3>Teacher-marked SAQs<\/h3>\n        <p>Submit written exam responses and receive chemistry specialist feedback with improvement guidance.<\/p>\n      <\/div>\n\n      <div class=\"ols-course-feature\">\n        <h3>Progress tracking<\/h3>\n        <p>Identify strengths and weaknesses across formulae, equations, mole calculations, concentrations, gas volumes, percentage yield and atom economy with targeted reporting.<\/p>\n      <\/div>\n\n    <\/div>\n\n    <div class=\"ols-course-cta-bottom\">\n      <a class=\"ols-course-button\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/product\/formulae-equations-and-amount-of-substance-edexcel-t1\/\">\n        View Formulae, Equations &amp; Amount of Substance Topic 1 Course\n      <\/a>\n    <\/div>\n\n  <\/div>\n\n<\/section>\n\n      <!-- FAQs -->\n      <section class=\"ols-faq-card\">\n        <h2>FAQs<\/h2>\n        <p>These questions address the most common points of confusion students encounter when working with ppm.<\/p>\n        <div class=\"ols-faq-list\">\n          <div class=\"ols-faq-item\">\n            <h3>What does ppm actually mean?<\/h3>\n            <p>ppm stands for &#8220;parts per million&#8221;. It tells you how many parts of solute (or gas) are present in 1 000 000 parts of the total sample. So 50 ppm means 50 parts in 1 000 000 parts. The word works in the same way as &#8220;percent&#8221;, which means out of 100.<\/p>\n          <\/div>\n          <div class=\"ols-faq-item\">\n            <h3>When should I use ppm instead of mol dm<sup>\u22123<\/sup>?<\/h3>\n            <p>ppm is used for very dilute concentrations, particularly trace pollutants in water and trace gases in air. For these, mol dm<sup>\u22123<\/sup> values would be tiny decimals that are awkward to write, so ppm gives a more readable whole number.<\/p>\n          <\/div>\n          <div class=\"ols-faq-item\">\n            <h3>Does it matter what units I use for the masses or volumes?<\/h3>\n            <p>No, as long as the units are the <strong>same on the top and the bottom<\/strong> of the fraction. The units cancel inside the formula, leaving ppm as a dimensionless number. If the question gives different units, convert one of them first.<\/p>\n          <\/div>\n          <div class=\"ols-faq-item\">\n            <h3>What is the difference between ppm for solutions and ppm for gases?<\/h3>\n            <p>The structure of the formula is identical, but the quantities differ. For <strong>solutions<\/strong>, use masses (mass of solute over mass of solvent). For <strong>gases in air<\/strong>, use volumes (volume of gas over volume of air). Choosing the wrong one is a common mistake.<\/p>\n          <\/div>\n          <div class=\"ols-faq-item\">\n            <h3>Is ppm the same as mg\/L for dilute aqueous solutions?<\/h3>\n            <p>For very dilute aqueous solutions, 1 ppm is approximately equal to 1 mg per dm<sup>3<\/sup> (1 mg\/L) because the density of dilute water is close to 1 g cm<sup>\u22123<\/sup>. This is a useful approximation but is not strictly part of the formula.<\/p>\n          <\/div>\n          <div class=\"ols-faq-item\">\n            <h3>How do I rearrange the ppm formula to find the mass or volume of solute?<\/h3>\n            <p>Multiply both sides of the formula by the mass (or volume) of the sample, then divide by 1 000 000. For gases this gives: volume of gas = (ppm \u00d7 volume of air) \u00f7 1 000 000.<\/p>\n          <\/div>\n        <\/div>\n      <\/section>\n\n      <!-- Related Topics -->\n      <section class=\"ols-related-card\">\n        <h2>Related Topics<\/h2>\n        <p>Build the surrounding skills needed to work confidently with dilute concentrations and solution chemistry.<\/p>\n        <div class=\"ols-related-grid\">\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/calculations-with-solutions-and-gases\/concentrations-of-solutions\/\">Concentrations of Solutions<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/calculations-with-solutions-and-gases\/molar-volume-calculations\/\">Molar Volume Calculations<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/mole-calculations\/\">Amount of Substance<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/empirical-and-molecular-formulae\/empirical-formulae\/\">Empirical Formula<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/empirical-and-molecular-formulae\/\">Formulae<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/\">Topic 1 Overview<\/a>\n        <\/div>\n      <\/section>\n\n      <!-- Copyright attribution -->\n      <section class=\"ols-attribution-card\">\n        <p><strong>Copyright notice:<\/strong> This OLS revision content, including the explanations, layout, diagrams, tables and embedded learning structure, is authored for Online Learning System by Dr. Mohammed Al-Fatah. It may not be copied, reproduced, redistributed or adapted without written permission.<\/p>\n      <\/section>\n\n      <!-- JSON-LD Schema -->\n      <script type=\"application\/ld+json\">\n      {\n        \"@context\": \"https:\/\/schema.org\",\n        \"@graph\": [\n          {\n            \"@type\": \"WebPage\",\n            \"@id\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/mole-calculations\/concentrations-in-ppm\/#webpage\",\n            \"url\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/mole-calculations\/concentrations-in-ppm\/\",\n            \"name\": \"Concentrations in PPM - Edexcel International A Level Chemistry Revision Notes\",\n            \"description\": \"Learn how to calculate concentrations in parts per million (ppm) for Edexcel International A Level Chemistry Topic 1. 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