{"id":8089,"date":"2026-09-15T08:24:41","date_gmt":"2026-09-15T07:24:41","guid":{"rendered":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-2-atoms-molecules-and-stoichiometry\/calculations-with-solutions-and-gases\/titration-calculations\/"},"modified":"2026-09-24T11:05:08","modified_gmt":"2026-09-24T10:05:08","slug":"titration-calculations","status":"publish","type":"page","link":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-2-atoms-molecules-and-stoichiometry\/calculations-with-solutions-and-gases\/titration-calculations\/","title":{"rendered":"Titration Calculations"},"content":{"rendered":"\n<!--\n===============================================================================\nONLINE LEARNING SYSTEM COPYRIGHT NOTICE\n\u00a9 Online Learning System. 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background: #2563eb !important;\n      color: #ffffff !important;\n    }\n\n    body.ols-lightbox-lock {\n      overflow: hidden !important;\n    }\n\n    @media (max-width: 760px) {\n      .ols-zoom-card {\n        border-radius: 22px !important;\n        overflow: hidden !important;\n      }\n\n      .ols-zoom-card-image {\n        min-height: auto !important;\n        padding: 12px !important;\n        overflow: hidden !important;\n        border-top-left-radius: 22px !important;\n        border-top-right-radius: 22px !important;\n      }\n\n      .ols-zoom-card img.ols-zoomable-img,\n      .ols-zoom-card img.ols-zoomable-img:hover {\n        transform: none !important;\n        box-shadow: none !important;\n      }\n\n      .ols-zoom-card-caption {\n        border-bottom-left-radius: 22px !important;\n        border-bottom-right-radius: 22px !important;\n      }\n\n      .ols-image-lightbox {\n        padding: 14px !important;\n      }\n\n      .ols-image-lightbox-img {\n        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<p>Cambridge International AS Level Chemistry<\/p>\n  <\/div>\n  <div class=\"ols-topic-group\">\n    <h4>Topic 2 Atoms, Molecules and Stoichiometry<\/h4>\n    <ul class=\"ols-topic-list\">\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-2-atoms-molecules-and-stoichiometry\/\">Topic overview<\/a><\/li>\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-2-atoms-molecules-and-stoichiometry\/atoms-elements-and-molecules\/\">2.1 \/ 2.2 Atoms, Elements and Molecules<\/a><\/li>\n<li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-2-atoms-molecules-and-stoichiometry\/ions-and-ionic-formulae\/\">2.3 Ions and Ionic Formulae<\/a><\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-2-atoms-molecules-and-stoichiometry\/equations-and-reaction-types\/\">2.3 Equations and Reaction Types<\/a>\n        <ul class=\"ols-subtopic-list\">\n          <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-2-atoms-molecules-and-stoichiometry\/equations-and-reaction-types\/writing-chemical-equations\/\">Writing Chemical Equations<\/a><\/li>\n          <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-2-atoms-molecules-and-stoichiometry\/equations-and-reaction-types\/typical-reactions-of-acids\/\">Typical Reactions of Acids<\/a><\/li>\n          <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-2-atoms-molecules-and-stoichiometry\/equations-and-reaction-types\/ionic-and-full-equations\/\">Ionic and Full Equations<\/a><\/li>\n        <\/ul>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-2-atoms-molecules-and-stoichiometry\/empirical-and-molecular-formulae\/\">2.3 Empirical and Molecular Formulae<\/a>\n        <ul class=\"ols-subtopic-list\">\n          <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-2-atoms-molecules-and-stoichiometry\/empirical-and-molecular-formulae\/empirical-formulae\/\">Empirical Formulae<\/a><\/li>\n          <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-2-atoms-molecules-and-stoichiometry\/empirical-and-molecular-formulae\/molecular-formulae\/\">Molecular Formulae<\/a><\/li>\n<li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-2-atoms-molecules-and-stoichiometry\/hydrated-salts-and-water-of-crystallisation\/\">2.3 Hydrated Salts and Water of Crystallisation<\/a><\/li>\n        <\/ul>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-2-atoms-molecules-and-stoichiometry\/mole-calculations\/\">2.4 Mole Calculations<\/a>\n        <ul class=\"ols-subtopic-list\">\n          <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-2-atoms-molecules-and-stoichiometry\/mole-calculations\/comparing-masses-of-substances\/\">Comparing Masses of Substances<\/a><\/li>\n          <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-2-atoms-molecules-and-stoichiometry\/mole-calculations\/calculations-involving-moles\/\">Calculations involving Moles<\/a><\/li>\n          <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-2-atoms-molecules-and-stoichiometry\/mole-calculations\/calculations-using-reacting-masses\/\">Calculations using Reacting Masses<\/a><\/li>\n          <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-2-atoms-molecules-and-stoichiometry\/mole-calculations\/the-yield-of-a-reaction\/\">The Yield of a Reaction<\/a><\/li>\n          <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-2-atoms-molecules-and-stoichiometry\/mole-calculations\/atom-economy\/\">Atom Economy<\/a><\/li>\n        <\/ul>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-2-atoms-molecules-and-stoichiometry\/calculations-with-solutions-and-gases\/\">2.4 Solutions and Gases<\/a>\n        <ul class=\"ols-subtopic-list\">\n          <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-2-atoms-molecules-and-stoichiometry\/calculations-with-solutions-and-gases\/molar-volume-calculations\/\">Molar Volume Calculations<\/a><\/li>\n          <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-2-atoms-molecules-and-stoichiometry\/calculations-with-solutions-and-gases\/concentrations-of-solutions\/\">Concentrations of Solutions<\/a><\/li>\n          <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-2-atoms-molecules-and-stoichiometry\/calculations-with-solutions-and-gases\/titration-calculations\/\">Titration Calculations<\/a><\/li>\n        <\/ul>\n      <\/li>\n    <\/ul>\n  <\/div>\n  <div class=\"ols-topic-group\">\n    <h4>Other Topics<\/h4>\n    <ul class=\"ols-topic-list\">\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-1-atomic-structure\/\">Topic 1 Atomic Structure<\/a><\/li>\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-3-chemical-bonding\/\">Topic 3 Chemical Bonding<\/a><\/li>\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-4-states-of-matter\/\">Topic 4 States of Matter<\/a><\/li>\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-9-the-periodic-table-chemical-periodicity\/\">Topic 9 Chemical Periodicity<\/a><\/li>\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-13-an-introduction-to-as-level-organic-chemistry\/\">Topic 13 Introduction to Organic Chemistry<\/a><\/li>\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-14-hydrocarbons\/\">Topic 14 Hydrocarbons<\/a><\/li>\n    <\/ul>\n  <\/div>\n<\/aside>\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      .replace(\/\\\/+$\/, '')\r\n      .toLowerCase();\r\n  }\r\n\r\n  function highlightActive() {\r\n    var sidebar = document.querySelector('.ols-sidebar');\r\n    if (!sidebar) return false;\r\n\r\n    var currentPath = normalisePath(window.location.pathname);\r\n    var links = sidebar.querySelectorAll('a[href]');\r\n    var matched = null;\r\n    var matchedLength = 0;\r\n\r\n    sidebar.querySelectorAll('.active, .active-main, .parent-active').forEach(function(item) {\r\n      item.classList.remove('active', 'active-main', 'parent-active');\r\n    });\r\n\r\n    sidebar.querySelectorAll('a[data-ols-disabled-parent=\"1\"], 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href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-2-atoms-molecules-and-stoichiometry\/calculations-with-solutions-and-gases\/\">Calculations with Solutions and Gases<\/a> \/\n<span>Titration Calculations<\/span>\n<\/nav>\n\n      <header class=\"ols-title-card\">\n        <h1>Titration Calculations<\/h1>\n        <p class=\"ols-page-intro\">A concise Cambridge International AS Level Chemistry revision guide to titration calculations: moles from concentration and volume, the mole ratio from the balanced equation, concordant titres and the mean titre, and unstructured problems on purity and relative molecular mass.<\/p>\n\n        <div class=\"ols-badges\">\n<div class=\"ols-badge\">AS Level<\/div>\n<div class=\"ols-badge\">Topic 2: Atoms, Molecules and Stoichiometry<\/div>\n<div class=\"ols-badge\">9701 Papers 1 and 2<\/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      <section class=\"ols-h5p-card ols-h5p-inline ols-h5p-recap\">\n<span class=\"ols-h5p-kicker\">Before you start<\/span>\n<h2>GCSE Recap: Neutralisation and Reacting Ratios<\/h2>\n<p>Before you start, check the GCSE chemistry this page is built on.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-content\" data-content-id=\"805\"><\/div><\/div>\n<\/section>\n<article class=\"ols-note-card soft\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">1<\/div>\n<h2>What a Titration Tells You<\/h2>\n<\/div>\n<p>A titration measures the exact volume of one solution needed to react completely with a measured volume of another. One solution has a known concentration (the <strong>standard solution<\/strong>); the other is the unknown. Because the balanced equation fixes the mole ratio, the volumes and the known concentration let you calculate the unknown concentration, an unknown volume, the relative molecular mass of an acid, or the purity of a sample.<\/p>\n<p>Every titration calculation follows the same four steps:<\/p>\n<ol>\n<li><strong>Moles of the known solution:<\/strong> n = c \u00d7 V (with V in dm\u00b3, so divide cm\u00b3 by 1000).<\/li>\n<li><strong>Mole ratio from the equation:<\/strong> read the coefficients to find moles of the other reactant.<\/li>\n<li><strong>Moles of the unknown:<\/strong> apply the ratio.<\/li>\n<li><strong>Convert to the quantity asked for:<\/strong> concentration (n \u00f7 V), volume (n \u00f7 c), mass (n \u00d7 M) or M<sub>r<\/sub> (m \u00f7 n).<\/li>\n<\/ol>\n<div class=\"ols-zoom-card\">\n<div class=\"ols-zoom-card-image\">\n<a class=\"ols-lightbox-link\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/09\/wave-18.jpg\" aria-label=\"Open image full screen\">\n<img decoding=\"async\" class=\"ols-zoomable-img ols-lightbox-target\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/09\/wave-18.jpg\" alt=\"Titration apparatus with a filled burette and a pipetted flask of indicator, beside a results table whose concordant titres agree within 0.10 cm\u00b3\">\n<\/a>\n<\/div>\n<div class=\"ols-zoom-card-caption\"><p>The burette delivers the standard solution into a pipetted volume of the unknown; the mean of the concordant titres is used in the calculation.<\/p><\/div>\n<\/div>\n<div class=\"ols-key-box\">\n<p><strong>Key idea:<\/strong> Known moles \u2192 ratio \u2192 unknown moles \u2192 answer. Write the four steps every time and the marks follow.<\/p>\n<\/div>\n<\/article>\n<article class=\"ols-note-card\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">2<\/div>\n<h2>Worked Example 1: Concentration of an Acid<\/h2>\n<\/div>\n<p>25.0 cm\u00b3 of sodium hydroxide solution of concentration 0.100 mol dm\u207b\u00b3 is neutralised by 21.40 cm\u00b3 of hydrochloric acid. Find the concentration of the acid.<\/p>\n<p><strong>NaOH + HCl \u2192 NaCl + H\u2082O<\/strong><\/p>\n<ol>\n<li>n(NaOH) = 0.100 \u00d7 25.0 \/ 1000 = 2.50 \u00d7 10\u207b\u00b3 mol<\/li>\n<li>Ratio NaOH : HCl = 1 : 1<\/li>\n<li>n(HCl) = 2.50 \u00d7 10\u207b\u00b3 mol<\/li>\n<li>c(HCl) = 2.50 \u00d7 10\u207b\u00b3 \/ (21.40 \/ 1000) = <strong>0.117 mol dm\u207b\u00b3<\/strong> (3 significant figures)<\/li>\n<\/ol>\n<div class=\"ols-key-box\">\n<p><strong>Exam sentence:<\/strong> Quote the answer to the same number of significant figures as the least precise piece of data, usually three.<\/p>\n<\/div>\n<\/article>\n<section class=\"ols-h5p-card ols-h5p-inline\">\n<span class=\"ols-h5p-kicker\">Check your understanding<\/span>\n<h2>Quick Check: A 1 : 1 Titration<\/h2>\n<p>Work it out on paper before you choose; three of the options come from the usual slips.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-499\" class=\"h5p-iframe\" data-content-id=\"499\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Titration Calculations MCQ: Concentration of an Alkali from a Titre\"><\/iframe><\/div><\/div>\n<\/section>\n<article class=\"ols-note-card purple\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">3<\/div>\n<h2>Worked Example 2: A 1 : 2 Ratio<\/h2>\n<\/div>\n<p>A 25.0 cm\u00b3 sample of sulfuric acid needs 18.75 cm\u00b3 of 0.200 mol dm\u207b\u00b3 potassium hydroxide for complete neutralisation. Find the concentration of the acid.<\/p>\n<p><strong>H\u2082SO\u2084 + 2KOH \u2192 K\u2082SO\u2084 + 2H\u2082O<\/strong><\/p>\n<ol>\n<li>n(KOH) = 0.200 \u00d7 18.75 \/ 1000 = 3.75 \u00d7 10\u207b\u00b3 mol<\/li>\n<li>Ratio H\u2082SO\u2084 : KOH = 1 : 2, so n(H\u2082SO\u2084) = 3.75 \u00d7 10\u207b\u00b3 \/ 2 = 1.875 \u00d7 10\u207b\u00b3 mol<\/li>\n<li>c(H\u2082SO\u2084) = 1.875 \u00d7 10\u207b\u00b3 \/ 0.0250 = <strong>0.0750 mol dm\u207b\u00b3<\/strong><\/li>\n<\/ol>\n<p>The ratio is where most marks are lost. A diprotic acid needs two moles of hydroxide per mole of acid, so the acid moles are <strong>half<\/strong> the alkali moles, not double.<\/p>\n<div class=\"ols-key-box\">\n<p><strong>Key idea:<\/strong> Decide the direction of the ratio by asking which substance the question wants: divide when going from the &#8220;2&#8221; reactant to the &#8220;1&#8221; reactant, multiply the other way.<\/p>\n<\/div>\n<\/article>\n<section class=\"ols-h5p-card ols-h5p-inline\">\n<span class=\"ols-h5p-kicker\">Check your understanding<\/span>\n<h2>Quick Check: Ratios in Both Directions<\/h2>\n<p>Work each titration out fully, then flip the card to compare your working.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-500\" class=\"h5p-iframe\" data-content-id=\"500\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Titration Calculations Flip Cards: Getting the Mole Ratio the Right Way Round\"><\/iframe><\/div><\/div>\n<\/section>\n<article class=\"ols-note-card\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">4<\/div>\n<h2>Mean Titres and Concordant Results<\/h2>\n<\/div>\n<p>A titration is repeated until two or more titres agree within 0.10 cm\u00b3; these are <strong>concordant<\/strong>. Only concordant titres are averaged, and the rough (first) titre is never included.<\/p>\n<div class=\"ols-table-wrap\">\n<table class=\"ols-table\">\n<thead>\n<tr><th>Titration<\/th><th>Rough<\/th><th>1<\/th><th>2<\/th><th>3<\/th><\/tr>\n<\/thead>\n<tbody>\n<tr><td><strong>Final reading \/ cm\u00b3<\/strong><\/td><td>24.10<\/td><td>47.45<\/td><td>23.40<\/td><td>46.85<\/td><\/tr>\n<tr><td><strong>Initial reading \/ cm\u00b3<\/strong><\/td><td>0.00<\/td><td>24.10<\/td><td>0.00<\/td><td>23.40<\/td><\/tr>\n<tr><td><strong>Titre \/ cm\u00b3<\/strong><\/td><td>24.10<\/td><td>23.35<\/td><td>23.40<\/td><td>23.45<\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<p>Titres 1, 2 and 3 are all within 0.10 cm\u00b3, so the mean titre is (23.35 + 23.40 + 23.45) \/ 3 = <strong>23.40 cm\u00b3<\/strong>. Burette readings are recorded to two decimal places, the second being 0 or 5.<\/p>\n<div class=\"ols-key-box\">\n<p><strong>Exam sentence:<\/strong> Concordant titres are those within 0.10 cm\u00b3 of each other; the mean titre is calculated from concordant titres only.<\/p>\n<\/div>\n<\/article>\n<section class=\"ols-h5p-card ols-h5p-inline\">\n<span class=\"ols-h5p-kicker\">Check your understanding<\/span>\n<h2>Quick Check: Choosing the Titres<\/h2>\n<p>Click every titre that belongs in that student&#039;s mean.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-501\" class=\"h5p-iframe\" data-content-id=\"501\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Titration Calculations Mark the Words: Which Titres Go into the Mean?\"><\/iframe><\/div><\/div>\n<\/section>\n<article class=\"ols-note-card orange\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">5<\/div>\n<h2>Unstructured Problems: Mass, Purity and Relative Molecular Mass<\/h2>\n<\/div>\n<p>Harder questions give no steps. The same four moves still apply; the only difference is what you convert to at the end.<\/p>\n<p><strong>Purity of a solid.<\/strong> 1.25 g of impure sodium carbonate is dissolved and made up to 250 cm\u00b3. A 25.0 cm\u00b3 portion needs 22.50 cm\u00b3 of 0.100 mol dm\u207b\u00b3 hydrochloric acid.<\/p>\n<p><strong>Na\u2082CO\u2083 + 2HCl \u2192 2NaCl + H\u2082O + CO\u2082<\/strong><\/p>\n<ol>\n<li>n(HCl) = 0.100 \u00d7 22.50 \/ 1000 = 2.25 \u00d7 10\u207b\u00b3 mol, so n(Na\u2082CO\u2083) in 25.0 cm\u00b3 = 1.125 \u00d7 10\u207b\u00b3 mol<\/li>\n<li>In the whole 250 cm\u00b3: 1.125 \u00d7 10\u207b\u00b3 \u00d7 10 = 1.125 \u00d7 10\u207b\u00b2 mol<\/li>\n<li>Mass of Na\u2082CO\u2083 = 1.125 \u00d7 10\u207b\u00b2 \u00d7 106.0 = 1.1925 g, so purity = 1.1925 \/ 1.25 \u00d7 100 = <strong>95.4%<\/strong><\/li>\n<\/ol>\n<p><strong>Relative molecular mass of an acid.<\/strong> If 0.500 g of a monoprotic acid HA needs 20.00 cm\u00b3 of 0.250 mol dm\u207b\u00b3 NaOH, then n(HA) = 5.00 \u00d7 10\u207b\u00b3 mol and M<sub>r<\/sub> = 0.500 \/ 5.00 \u00d7 10\u207b\u00b3 = <strong>100<\/strong>.<\/p>\n<div class=\"ols-key-box\">\n<p><strong>Key idea:<\/strong> When a sample is made up to 250 cm\u00b3 and 25.0 cm\u00b3 portions are titrated, scale the moles in the portion up by 10 before converting to mass.<\/p>\n<\/div>\n<\/article>\n<section class=\"ols-h5p-card ols-h5p-inline\">\n<span class=\"ols-h5p-kicker\">Check your understanding<\/span>\n<h2>Quick Check: Purity and Relative Molecular Mass<\/h2>\n<p>Four problems with no steps given; type the final answer for each.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-498\" class=\"h5p-iframe\" data-content-id=\"498\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Titration Calculations Flashcards: Purity and Relative Molecular Mass\"><\/iframe><\/div><\/div>\n<\/section>\n<section class=\"ols-h5p-card ols-h5p-inline\">\n<span class=\"ols-h5p-kicker\">Check your understanding<\/span>\n<h2>Quick Check: Pick the Accurate Statement<\/h2>\n<p>In each round, choose the one statement that is accurate.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-806\" class=\"h5p-iframe\" data-content-id=\"806\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Titration Calculations Summary: Where the Marks Are Lost\"><\/iframe><\/div><\/div>\n<\/section>\n<article class=\"ols-note-card soft\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">6<\/div>\n<h2>Common Exam Mistakes<\/h2>\n<\/div>\n<ul>\n<li>Forgetting to convert cm\u00b3 to dm\u00b3 before using n = c \u00d7 V.<\/li>\n<li>Applying the mole ratio the wrong way round for diprotic acids or carbonates.<\/li>\n<li>Including the rough titre in the mean, or averaging titres that are not concordant.<\/li>\n<li>Using the pipette volume where the burette volume belongs, or the reverse.<\/li>\n<li>Rounding too early: keep at least four figures until the final answer.<\/li>\n<\/ul>\n<div class=\"ols-key-box\">\n<p><strong>Exam sentence:<\/strong> Moles of the standard solution from c \u00d7 V, moles of the unknown from the equation ratio, then the quantity asked for.<\/p>\n<\/div>\n<\/article>\n\n<section class=\"ols-related-card\">\n        <h2>Related Topics<\/h2>\n        <p>Continue through Topic 2 by linking this page to equations, formulae and mole calculation revision.<\/p>\n        <div class=\"ols-related-grid\">\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-2-atoms-molecules-and-stoichiometry\/equations-and-reaction-types\/\">Equations and Reaction Types<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-2-atoms-molecules-and-stoichiometry\/equations-and-reaction-types\/writing-chemical-equations\/\">Writing Chemical Equations<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-2-atoms-molecules-and-stoichiometry\/mole-calculations\/\">Mole Calculations<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-2-atoms-molecules-and-stoichiometry\/empirical-and-molecular-formulae\/\">Empirical and Molecular Formulae<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-2-atoms-molecules-and-stoichiometry\/calculations-with-solutions-and-gases\/\">Calculations with Solutions and Gases<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-1-atomic-structure\/\">Atomic Structure &amp; The Periodic Table<\/a>\n        <\/div>\n      <\/section>\n\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. 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