{"id":4014,"date":"2026-05-21T07:04:42","date_gmt":"2026-05-21T06:04:42","guid":{"rendered":"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\/"},"modified":"2026-06-28T05:52:17","modified_gmt":"2026-06-28T04:52:17","slug":"molecular-formulae","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\/empirical-and-molecular-formulae\/molecular-formulae\/","title":{"rendered":"Molecular Formulae"},"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-MOLECULAR-FORMULA-REVISION-PAGE-2026\n\nPage:\nMolecular Formula\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-molecular-formula-page\" data-owner=\"Online Learning System\" data-copyright=\"\u00a9 Online Learning System. 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Molecular Formula.\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      .replace(\/\\\/+$|\\s+$\/g, '')\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  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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\/empirical-and-molecular-formulae\/\">Formulae<\/a> \/\n        <span>Molecular Formula<\/span>\n      <\/nav>\n\n      <header class=\"ols-title-card\">\n        <h1>Molecular Formula<\/h1>\n        <p class=\"ols-page-intro\">A focused revision guide to molecular formulae for Edexcel International A Level Chemistry. This page shows how to move from an empirical formula to the actual molecular formula using relative molecular mass, percentage composition and clear worked examples.<\/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      <article class=\"ols-note-card soft\">\n        <div class=\"ols-note-title\"><div class=\"ols-note-icon\">1<\/div><h2>What Is a Molecular Formula?<\/h2><\/div>\n        <p>The <strong>molecular formula<\/strong> shows the actual number of atoms of each element in one molecule of a compound. It gives more information than an empirical formula because it tells you the real atom count, not just the simplest ratio.<\/p>\n        <p>For example, the empirical formula of glucose is CH<sub>2<\/sub>O, but the molecular formula is <strong>C<sub>6<\/sub>H<sub>12<\/sub>O<sub>6<\/sub><\/strong>. The molecular formula is six times the empirical formula unit.<\/p>\n        <div class=\"ols-definition-box\">\n          <p><strong>Definition:<\/strong> A molecular formula is the <strong>actual number of atoms<\/strong> of each element in one molecule of the compound.<\/p>\n        <\/div>\n        <div class=\"ols-key-box\">\n          <p><strong>Key distinction:<\/strong> an empirical formula gives the simplest ratio, while a molecular formula gives the actual formula of a molecule.<\/p>\n        <\/div>\n      <\/article>\n\n      <article class=\"ols-note-card\">\n        <div class=\"ols-note-title\"><div class=\"ols-note-icon\">2<\/div><h2>The Core Relationship<\/h2><\/div>\n        <p>To find a molecular formula from an empirical formula, compare the relative molecular mass of the whole compound with the relative formula mass of the empirical formula unit.<\/p>\n        <div class=\"ols-definition-box\">\n          <p><strong>n = M<sub>r<\/sub> of compound \u00f7 M<sub>r<\/sub> of empirical formula unit<\/strong><\/p>\n        <\/div>\n        <p>Then multiply every subscript in the empirical formula by <strong>n<\/strong>. The value of n should be a whole number because one molecule contains a whole-number multiple of the empirical formula unit.<\/p>\n        <div class=\"ols-rule-list\">\n          <div class=\"ols-rule-item\">\n            <h3>Step 1 \u2014 Find the M<sub>r<\/sub> of the empirical formula<\/h3>\n            <p>Add the relative atomic masses for one empirical formula unit.<\/p>\n          <\/div>\n          <div class=\"ols-rule-item\">\n            <h3>Step 2 \u2014 Divide the compound M<sub>r<\/sub> by the empirical formula M<sub>r<\/sub><\/h3>\n            <p>This gives the multiplier, n.<\/p>\n          <\/div>\n          <div class=\"ols-rule-item\">\n            <h3>Step 3 \u2014 Multiply the empirical formula by n<\/h3>\n            <p>Multiply every element subscript by the same multiplier to get the molecular formula.<\/p>\n          <\/div>\n        <\/div>\n      <\/article>\n\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\/How-to-convert-empirical-to-molecular-formula.webp\" alt=\"How to convert an empirical formula into a molecular formula using relative molecular mass\" class=\"ols-zoomable-img ols-lightbox-target\" draggable=\"false\">\n        <\/div>\n        <div class=\"ols-zoom-card-caption\">\n          <p>The molecular formula is found by checking how many times the empirical formula mass fits into the relative molecular mass of the compound.<\/p>\n        <\/div>\n      <\/div>\n\n      <article class=\"ols-note-card purple\">\n        <div class=\"ols-note-title\"><div class=\"ols-note-icon\">3<\/div><h2>Worked Example: Empirical Formula Given<\/h2><\/div>\n        <p>Determine the molecular formula of a compound with empirical formula <strong>C<sub>3<\/sub>H<sub>6<\/sub>O<\/strong> and M<sub>r<\/sub> = <strong>116<\/strong>.<\/p>\n\n        <div class=\"ols-worked-example\">\n          <h3>Step 1 \u2014 Find the M<sub>r<\/sub> of the empirical formula<\/h3>\n          <div class=\"ols-calc-row\">\n            <div class=\"ols-calc-cell\"><span>C<sub>3<\/sub><\/span>3 \u00d7 12 = <strong>36<\/strong><\/div>\n            <div class=\"ols-calc-cell\"><span>H<sub>6<\/sub><\/span>6 \u00d7 1 = <strong>6<\/strong><\/div>\n            <div class=\"ols-calc-cell\"><span>O<\/span>1 \u00d7 16 = <strong>16<\/strong><\/div>\n          <\/div>\n          <p>M<sub>r<\/sub> of C<sub>3<\/sub>H<sub>6<\/sub>O = 36 + 6 + 16 = <strong>58<\/strong>.<\/p>\n        <\/div>\n\n        <div class=\"ols-worked-example\">\n          <h3>Step 2 \u2014 Find the multiplier<\/h3>\n          <p>n = 116 \u00f7 58 = <strong>2<\/strong>.<\/p>\n        <\/div>\n\n        <div class=\"ols-key-box\">\n          <p><strong>Molecular formula: C<sub>6<\/sub>H<sub>12<\/sub>O<sub>2<\/sub><\/strong>. The empirical formula C<sub>3<\/sub>H<sub>6<\/sub>O has been multiplied by 2.<\/p>\n        <\/div>\n      <\/article>\n\n      <article class=\"ols-note-card orange\">\n        <div class=\"ols-note-title\"><div class=\"ols-note-icon\">4<\/div><h2>Shortcut Method from Percentage Composition<\/h2><\/div>\n        <p>If you are given percentage composition and the relative molecular mass of the compound, you can find the molecular formula directly. Instead of first writing the empirical formula, find the mass of each element in one mole of the compound.<\/p>\n        <p>For a compound with M<sub>r<\/sub> = 46 containing <strong>52.2% C<\/strong>, <strong>13.0% H<\/strong> and <strong>34.8% O<\/strong>, the percentage tells you what fraction of the 46 g mol<sup>-1<\/sup> belongs to each element.<\/p>\n\n        <div class=\"ols-worked-example\">\n          <h3>Step 1 \u2014 Find the mass of each element in one mole<\/h3>\n          <div class=\"ols-calc-row\">\n            <div class=\"ols-calc-cell\"><span>Carbon<\/span>52.2% of 46 = <strong>24.01 g<\/strong><\/div>\n            <div class=\"ols-calc-cell\"><span>Hydrogen<\/span>13.0% of 46 = <strong>5.98 g<\/strong><\/div>\n            <div class=\"ols-calc-cell\"><span>Oxygen<\/span>34.8% of 46 = <strong>16.01 g<\/strong><\/div>\n          <\/div>\n        <\/div>\n\n        <div class=\"ols-worked-example\">\n          <h3>Step 2 \u2014 Convert each mass into moles of atoms<\/h3>\n          <div class=\"ols-calc-row\">\n            <div class=\"ols-calc-cell\"><span>C<\/span>24.01 \u00f7 12 \u2248 <strong>2<\/strong><\/div>\n            <div class=\"ols-calc-cell\"><span>H<\/span>5.98 \u00f7 1 \u2248 <strong>6<\/strong><\/div>\n            <div class=\"ols-calc-cell\"><span>O<\/span>16.01 \u00f7 16 \u2248 <strong>1<\/strong><\/div>\n          <\/div>\n        <\/div>\n\n        <div class=\"ols-key-box\">\n          <p><strong>Molecular formula: C<sub>2<\/sub>H<sub>6<\/sub>O<\/strong>. This shortcut works because the percentage composition is applied to one mole of compound.<\/p>\n        <\/div>\n      <\/article>\n\n      <article class=\"ols-note-card\">\n        <div class=\"ols-note-title\"><div class=\"ols-note-icon\">5<\/div><h2>When the M<sub>r<\/sub> Is Not Exact<\/h2><\/div>\n        <p>The relative molecular mass does not always need to match perfectly because experimental data may contain rounding. The important point is that the molecular formula must be a <strong>whole-number multiple<\/strong> of the empirical formula.<\/p>\n        <div class=\"ols-table-wrap\">\n          <table class=\"ols-table\">\n            <thead>\n              <tr>\n                <th>Calculation<\/th>\n                <th>Likely value of n<\/th>\n                <th>Exam decision<\/th>\n              <\/tr>\n            <\/thead>\n            <tbody>\n              <tr>\n                <td data-label=\"Calculation\">119.8 \u00f7 60 = 1.997<\/td>\n                <td data-label=\"Likely value of n\">2<\/td>\n                <td data-label=\"Exam decision\">Round to 2 because the value is extremely close to a whole number.<\/td>\n              <\/tr>\n              <tr>\n                <td data-label=\"Calculation\">178.9 \u00f7 30 = 5.963<\/td>\n                <td data-label=\"Likely value of n\">6<\/td>\n                <td data-label=\"Exam decision\">Round to 6 if the data clearly supports a whole-number multiple.<\/td>\n              <\/tr>\n              <tr>\n                <td data-label=\"Calculation\">116 \u00f7 58 = 2<\/td>\n                <td data-label=\"Likely value of n\">2<\/td>\n                <td data-label=\"Exam decision\">Use 2 directly.<\/td>\n              <\/tr>\n            <\/tbody>\n          <\/table>\n        <\/div>\n        <div class=\"ols-key-box\">\n          <p><strong>Exam tip:<\/strong> never multiply only one element. The multiplier applies to the whole empirical formula unit.<\/p>\n        <\/div>\n      <\/article>\n\n      <article class=\"ols-note-card purple\">\n        <div class=\"ols-note-title\"><div class=\"ols-note-icon\">6<\/div><h2>Empirical Formula vs Molecular Formula<\/h2><\/div>\n        <p>Different compounds may have the same empirical formula but different molecular formulae. This is why relative molecular mass is needed to identify the actual molecular formula.<\/p>\n        <div class=\"ols-table-wrap\">\n          <table class=\"ols-table\">\n            <thead>\n              <tr>\n                <th>Empirical formula<\/th>\n                <th>Empirical formula M<sub>r<\/sub><\/th>\n                <th>Compound M<sub>r<\/sub><\/th>\n                <th>n<\/th>\n                <th>Molecular formula<\/th>\n              <\/tr>\n            <\/thead>\n            <tbody>\n              <tr>\n                <td data-label=\"Empirical formula\">CH<sub>2<\/sub>O<\/td>\n                <td data-label=\"Empirical formula Mr\">30<\/td>\n                <td data-label=\"Compound Mr\">30<\/td>\n                <td data-label=\"n\">1<\/td>\n                <td data-label=\"Molecular formula\">CH<sub>2<\/sub>O<\/td>\n              <\/tr>\n              <tr>\n                <td data-label=\"Empirical formula\">CH<sub>2<\/sub>O<\/td>\n                <td data-label=\"Empirical formula Mr\">30<\/td>\n                <td data-label=\"Compound Mr\">60<\/td>\n                <td data-label=\"n\">2<\/td>\n                <td data-label=\"Molecular formula\">C<sub>2<\/sub>H<sub>4<\/sub>O<sub>2<\/sub><\/td>\n              <\/tr>\n              <tr>\n                <td data-label=\"Empirical formula\">CH<sub>2<\/sub>O<\/td>\n                <td data-label=\"Empirical formula Mr\">30<\/td>\n                <td data-label=\"Compound Mr\">180<\/td>\n                <td data-label=\"n\">6<\/td>\n                <td data-label=\"Molecular formula\">C<sub>6<\/sub>H<sub>12<\/sub>O<sub>6<\/sub><\/td>\n              <\/tr>\n              <tr>\n                <td data-label=\"Empirical formula\">HO<\/td>\n                <td data-label=\"Empirical formula Mr\">17<\/td>\n                <td data-label=\"Compound Mr\">34<\/td>\n                <td data-label=\"n\">2<\/td>\n                <td data-label=\"Molecular formula\">H<sub>2<\/sub>O<sub>2<\/sub><\/td>\n              <\/tr>\n            <\/tbody>\n          <\/table>\n        <\/div>\n      <\/article>\n\n      <article class=\"ols-note-card soft\">\n        <div class=\"ols-note-title\"><div class=\"ols-note-icon\">7<\/div><h2>Common Exam Points<\/h2><\/div>\n        <ul>\n          <li>The molecular formula shows the <strong>actual number of atoms<\/strong> of each element in one molecule.<\/li>\n          <li>The empirical formula shows the <strong>simplest whole-number ratio<\/strong> of atoms.<\/li>\n          <li>To move from empirical formula to molecular formula, you must be given the compound M<sub>r<\/sub> or enough data to work it out.<\/li>\n          <li>Find the M<sub>r<\/sub> of the empirical formula unit before calculating the multiplier.<\/li>\n          <li>The multiplier must be a whole number, allowing for sensible rounding of experimental data.<\/li>\n          <li>Apply the multiplier to every atom in the empirical formula, not just the first element.<\/li>\n          <li>If n = 1, the empirical formula and molecular formula are the same.<\/li>\n          <li>Ionic compounds are normally represented by formula units, so the language of molecular formula is mainly used for covalent molecular substances.<\/li>\n        <\/ul>\n      <\/article>\n\n      <section class=\"ols-h5p-card\">\n        <h2>Check Your Understanding<\/h2>\n        <p>Use these activities to practise converting empirical formulae into molecular formulae and recognising how relative molecular mass controls the multiplier.<\/p>\n        <div class=\"ols-h5p-grid\">\n          <div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-313\" class=\"h5p-iframe\" data-content-id=\"313\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Empirical and Molecular Formula Practice\"><\/iframe><\/div><\/div>\n          <div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-314\" class=\"h5p-iframe\" data-content-id=\"314\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Molecular Formula from Percentage Composition\"><\/iframe><\/div><\/div>\n          <div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-328\" class=\"h5p-iframe\" data-content-id=\"328\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Molecular formula of a hydrocarbon containing 82.8 percent carbon by mass\"><\/iframe><\/div><\/div>\n        <\/div>\n      <\/section>\n\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>Molecular formula:<\/strong> the actual number of atoms of each element in one molecule.<\/li>\n          <li><strong>Empirical formula:<\/strong> the simplest whole-number ratio of atoms in a compound.<\/li>\n          <li><strong>Multiplier:<\/strong> n = M<sub>r<\/sub> of compound \u00f7 M<sub>r<\/sub> of empirical formula unit.<\/li>\n          <li><strong>Method:<\/strong> find the empirical formula M<sub>r<\/sub>, calculate n, then multiply every subscript by n.<\/li>\n          <li><strong>Rounding:<\/strong> experimental M<sub>r<\/sub> data may not be exact, but n should be rounded sensibly to a whole number.<\/li>\n          <li><strong>Shortcut method:<\/strong> percentage composition and M<sub>r<\/sub> can be used together to find the mass of each element in one mole of compound.<\/li>\n          <li><strong>Common error:<\/strong> do not multiply only one element. The whole empirical formula unit is multiplied.<\/li>\n        <\/ul>\n      <\/section>\n\n      <div class=\"ols-image-lightbox\" id=\"olsImageLightboxMolecularFormula001\" 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 decoding=\"async\" class=\"ols-image-lightbox-img\" src=\"\" alt=\"\">\n        <\/div>\n      <\/div>\n\n      <script>\n        (function(){\n          var page = document.querySelector(\".ols-molecular-formula-page\");\n          if (!page) { return; }\n          var lightbox = page.querySelector(\"#olsImageLightboxMolecularFormula001\");\n          if (!lightbox) { return; }\n          var lightboxImage = lightbox.querySelector(\".ols-image-lightbox-img\");\n          var closeButton = 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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 empirical formulae, molecular formulae, mole calculations, reacting masses, gas volumes, 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, empirical formulae, 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\n\n      <section class=\"ols-faq-card\">\n        <h2>FAQs<\/h2>\n        <p>These questions address the most common points of confusion students encounter when converting empirical formulae into molecular formulae.<\/p>\n        <div class=\"ols-faq-list\">\n          <div class=\"ols-faq-item\">\n            <h3>What is the difference between an empirical formula and a molecular formula?<\/h3>\n            <p>The empirical formula shows the simplest whole-number ratio of atoms in a compound. The molecular formula shows the actual number of atoms of each element in one molecule. For example, CH<sub>2<\/sub>O can be an empirical formula, while C<sub>6<\/sub>H<sub>12<\/sub>O<sub>6<\/sub> is the molecular formula of glucose.<\/p>\n          <\/div>\n          <div class=\"ols-faq-item\">\n            <h3>How do I find the molecular formula from the empirical formula?<\/h3>\n            <p>Find the M<sub>r<\/sub> of the empirical formula unit, divide the compound M<sub>r<\/sub> by this value, then multiply every subscript in the empirical formula by the answer.<\/p>\n          <\/div>\n          <div class=\"ols-faq-item\">\n            <h3>What if the M<sub>r<\/sub> division does not give an exact whole number?<\/h3>\n            <p>Small differences can occur because of rounding in experimental data. If the value is very close to a whole number, round sensibly. A molecular formula must be a whole-number multiple of the empirical formula.<\/p>\n          <\/div>\n          <div class=\"ols-faq-item\">\n            <h3>Can the empirical formula and molecular formula be the same?<\/h3>\n            <p>Yes. If the multiplier n is 1, the empirical formula and molecular formula are identical. Water is H<sub>2<\/sub>O as both its empirical and molecular formula.<\/p>\n          <\/div>\n          <div class=\"ols-faq-item\">\n            <h3>Can I find the molecular formula directly from percentage composition?<\/h3>\n            <p>Yes, if the compound M<sub>r<\/sub> is also given. Find the mass of each element in one mole of compound using the percentage composition, then divide by the relevant A<sub>r<\/sub> values to find the number of atoms of each element.<\/p>\n          <\/div>\n        <\/div>\n      <\/section>\n\n      <section class=\"ols-related-card\">\n        <h2>Related Topics<\/h2>\n        <p>Build the surrounding skills needed to work confidently with formulae and mole calculations.<\/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\/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\/mole-calculations\/calculations-involving-moles\/\">Calculations Involving Moles<\/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\/calculations-using-reacting-masses\/\">Calculations Using Reacting Masses<\/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\/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\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/\">Topic 1 Overview<\/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. It may not be copied, reproduced, redistributed or adapted without written permission.<\/p>\n      <\/section>\n\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\/empirical-and-molecular-formulae\/molecular-formula\/#webpage\",\n            \"url\": \"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-formula\/\",\n            \"name\": \"Molecular Formula - Edexcel International A Level Chemistry Revision Notes\",\n            \"description\": \"Learn how to find molecular formulae from empirical formulae and relative molecular mass for Edexcel International A Level Chemistry Topic 1. 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