{"id":5275,"date":"2026-06-19T04:54:59","date_gmt":"2026-06-19T03:54:59","guid":{"rendered":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-1-2-amount-of-substance\/empirical-and-molecular-formulae\/"},"modified":"2026-06-24T08:50:54","modified_gmt":"2026-06-24T07:50:54","slug":"empirical-and-molecular-formulae","status":"publish","type":"page","link":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-1-2-amount-of-substance\/empirical-and-molecular-formulae\/","title":{"rendered":"Empirical and Molecular Formulae"},"content":{"rendered":"\n<div class=\"ols-aqa312emf-page\">\n\n  <aside class=\"ols-sidebar\">\r\n  <div class=\"ols-sidebar-header\">\r\n    <h3>Revision Notes<\/h3>\r\n    <p>AQA A Level Chemistry<\/p>\r\n  <\/div>\r\n\r\n  <div class=\"ols-topic-group\">\r\n    <h4>3.1.2 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\/aqa\/3-1-2-amount-of-substance\/relative-masses\/\">Relative Masses<\/a>\r\n      <\/li>\r\n\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-1-2-amount-of-substance\/the-mole-and-avogadro-constant\/\">The Mole and Avogadro Constant<\/a>\r\n      <\/li>\r\n\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-1-2-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\/aqa\/3-1-2-amount-of-substance\/empirical-and-molecular-formulae\/empirical-formula\/\">Empirical Formula<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-1-2-amount-of-substance\/empirical-and-molecular-formulae\/molecular-formula\/\">Molecular Formula<\/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\/aqa\/3-1-2-amount-of-substance\/chemical-equations-and-reacting-masses\/\">Chemical Equations and Reacting Masses<\/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\/aqa\/3-1-2-amount-of-substance\/chemical-equations-and-reacting-masses\/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\/aqa\/3-1-2-amount-of-substance\/chemical-equations-and-reacting-masses\/ionic-equations\/\">Ionic Equations<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-1-2-amount-of-substance\/chemical-equations-and-reacting-masses\/calculations-using-reacting-masses\/\">Calculations Using Reacting Masses<\/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\/aqa\/3-1-2-amount-of-substance\/concentration-and-titration-calculations\/\">Concentration and Titration 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\/aqa\/3-1-2-amount-of-substance\/concentration-and-titration-calculations\/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\/aqa\/3-1-2-amount-of-substance\/concentration-and-titration-calculations\/titration-calculations\/\">Titration Calculations<\/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\/aqa\/3-1-2-amount-of-substance\/gas-volumes-and-the-ideal-gas-equation\/\">Gas Volumes and the Ideal Gas Equation<\/a>\r\n      <\/li>\r\n\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-1-2-amount-of-substance\/percentage-yield\/\">Percentage Yield<\/a>\r\n      <\/li>\r\n\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-1-2-amount-of-substance\/atom-economy\/\">Atom Economy<\/a>\r\n      <\/li>\r\n    <\/ul>\r\n  <\/div>\r\n\r\n  <div class=\"ols-topic-group\">\r\n    <h4>Adjacent 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\/aqa\/3-1-1-atomicstructure\/\">3.1.1 Atomic Structure<\/a>\r\n      <\/li>\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-1-3-bonding\/\">3.1.3 Bonding<\/a>\r\n      <\/li>\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-1-4-energetics\/\">3.1.4 Energetics<\/a>\r\n      <\/li>\r\n      <li>\r\n        <a 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<nav class=\"ols-aqa312emf-breadcrumb\" aria-label=\"Breadcrumb\">\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/\">Revision Notes<\/a> \/\n        <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\/aqa\/\">AQA<\/a> \/\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-1-2-amount-of-substance\/\">3.1.2 Amount of Substance<\/a> \/\n        <span>Empirical and Molecular Formulae<\/span>\n      <\/nav>\n    <\/div>\n  <\/div>\n\n  <!-- INTRO -->\n  <section class=\"ols-aqa312emf-intro\">\n    <div class=\"ols-aqa312emf-container\">\n      <div class=\"ols-aqa312emf-intro-inner\">\n        <div>\n          <div class=\"ols-aqa312emf-eyebrow\">AQA A Level Chemistry<\/div>\n          <h1>Empirical<br>and Molecular<br>Formulae<\/h1>\n          <div class=\"ols-aqa312emf-accent-bar\"><\/div>\n          <p class=\"ols-aqa312emf-intro-lead\">\n            This AQA 3.1.2 section explains how formulas show chemical composition. Students learn the difference between empirical formula and molecular formula, how to calculate empirical formula from mass or percentage composition, and how to use relative molecular mass to find the molecular formula.\n          <\/p>\n        <\/div>\n\n        <div class=\"ols-aqa312emf-info-grid\">\n          <div class=\"ols-aqa312emf-info-card\"><div class=\"ols-aqa312emf-info-card-label\">Exam Papers<\/div><div class=\"ols-aqa312emf-info-card-value\">Paper 1 &amp; 2<\/div><div class=\"ols-aqa312emf-info-card-sub\">7405\/1 and 7405\/2<\/div><\/div>\n          <div class=\"ols-aqa312emf-info-card\"><div class=\"ols-aqa312emf-info-card-label\">Specification Point<\/div><div class=\"ols-aqa312emf-info-card-value\">3.1.2.4<\/div><div class=\"ols-aqa312emf-info-card-sub\">Empirical and molecular formula<\/div><\/div>\n          <div class=\"ols-aqa312emf-info-card\"><div class=\"ols-aqa312emf-info-card-label\">Topic Parts<\/div><div class=\"ols-aqa312emf-info-card-value\">2 parts<\/div><div class=\"ols-aqa312emf-info-card-sub\">Revision notes available<\/div><\/div>\n          <div class=\"ols-aqa312emf-info-card\"><div class=\"ols-aqa312emf-info-card-label\">Exam Board<\/div><div class=\"ols-aqa312emf-info-card-value\">AQA<\/div><div class=\"ols-aqa312emf-info-card-sub\">AQA 7405<\/div><\/div>\n        <\/div>\n      <\/div>\n    <\/div>\n  <\/section>\n\n  <!-- TOPIC CARDS -->\n  <section class=\"ols-aqa312emf-topics\">\n    <div class=\"ols-aqa312emf-container\">\n      <div class=\"ols-aqa312emf-section-header\">\n        <h2 class=\"ols-aqa312emf-section-title\">Revision Notes<\/h2>\n        <p class=\"ols-aqa312emf-section-sub\">Work through empirical and molecular formulae in a structured AQA sequence.<\/p>\n      <\/div>\n\n      <div class=\"ols-aqa312emf-cards-grid\">\n\n        <!-- Card 1: Empirical Formula -->\n        <a class=\"ols-aqa312emf-card ols-aqa312emf-card--available\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-1-2-amount-of-substance\/empirical-and-molecular-formulae\/empirical-formula\/\">\n          <div class=\"ols-aqa312emf-card-img-wrap\">\n            <div class=\"ols-aqa312emf-visual ols-aqa312emf-visual--empirical\">\n              <div class=\"ols-aqa312emf-visual-panel\">\n                <div class=\"ols-aqa312emf-visual-kicker\">Simplest ratio<\/div>\n                <div class=\"ols-aqa312emf-visual-main\">Empirical<br>Formula<\/div>\n                <div class=\"ols-aqa312emf-config-line\" aria-hidden=\"true\"><span>CH<sub>2<\/sub>O<\/span><\/div>\n              <\/div>\n            <\/div>\n            <div class=\"ols-aqa312emf-card-num\">1<\/div>\n            <span class=\"ols-aqa312emf-card-status ols-aqa312emf-card-status--available\">Available<\/span>\n          <\/div>\n          <div class=\"ols-aqa312emf-card-body\">\n            <p class=\"ols-aqa312emf-card-title\">Empirical Formula<\/p>\n            <p class=\"ols-aqa312emf-card-desc\">Calculating the simplest whole number ratio of atoms from composition by mass or percentage by mass.<\/p>\n            <span class=\"ols-aqa312emf-card-cta\">\n              Start revising\n              <svg viewBox=\"0 0 16 16\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\" stroke-linecap=\"round\" stroke-linejoin=\"round\"><path d=\"M3 8h10M9 4l4 4-4 4\"><\/path><\/svg>\n            <\/span>\n          <\/div>\n        <\/a>\n\n        <!-- Card 2: Molecular Formula -->\n        <a class=\"ols-aqa312emf-card ols-aqa312emf-card--available\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-1-2-amount-of-substance\/empirical-and-molecular-formulae\/molecular-formula\/\">\n          <div class=\"ols-aqa312emf-card-img-wrap\">\n            <div class=\"ols-aqa312emf-visual ols-aqa312emf-visual--molecular\">\n              <div class=\"ols-aqa312emf-visual-panel\">\n                <div class=\"ols-aqa312emf-visual-kicker\">Actual formula<\/div>\n                <div class=\"ols-aqa312emf-visual-main\">Molecular<br>Formula<\/div>\n                <div class=\"ols-aqa312emf-config-line\" aria-hidden=\"true\"><span>C<sub>6<\/sub>H<sub>12<\/sub>O<sub>6<\/sub><\/span><\/div>\n              <\/div>\n            <\/div>\n            <div class=\"ols-aqa312emf-card-num\">2<\/div>\n            <span class=\"ols-aqa312emf-card-status ols-aqa312emf-card-status--available\">Available<\/span>\n          <\/div>\n          <div class=\"ols-aqa312emf-card-body\">\n            <p class=\"ols-aqa312emf-card-title\">Molecular Formula<\/p>\n            <p class=\"ols-aqa312emf-card-desc\">Using the empirical formula and relative molecular mass to find the actual number of atoms in a molecule.<\/p>\n            <span class=\"ols-aqa312emf-card-cta\">\n              Start revising\n              <svg viewBox=\"0 0 16 16\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\" stroke-linecap=\"round\" stroke-linejoin=\"round\"><path d=\"M3 8h10M9 4l4 4-4 4\"><\/path><\/svg>\n            <\/span>\n          <\/div>\n        <\/a>\n\n      <\/div>\n    <\/div>\n  <\/section>\n\n  <!-- SPECIFICATION -->\n  <section class=\"ols-aqa312emf-spec-section\">\n    <div class=\"ols-aqa312emf-container\">\n\n      <!-- DESKTOP SPECIFICATION -->\n      <div class=\"ols-aqa312emf-spec-desktop\">\n        <div class=\"ols-aqa312emf-spec-wrap\">\n          <div class=\"ols-aqa312emf-spec-pill\">Specification Coverage<\/div>\n          <h2 class=\"ols-aqa312emf-spec-heading\">3.1.2.4 Empirical and Molecular Formula &#8211; AQA A Level Chemistry<\/h2>\n          <p class=\"ols-aqa312emf-spec-intro-text\">The following AQA specification points outline the knowledge and skills students are expected to demonstrate for empirical and molecular formulae.<\/p>\n\n          <h3 class=\"ols-aqa312emf-spec-group-title\">3.1.2.4 Empirical and molecular formula<\/h3>\n          <div class=\"ols-aqa312emf-spec-rows\">\n            <div class=\"ols-aqa312emf-spec-row ols-aqa312emf-spec-row--light\">\n              <div class=\"ols-aqa312emf-spec-code\">EF<\/div>\n              <div class=\"ols-aqa312emf-spec-text\">Empirical formula is the simplest whole number ratio of atoms of each element in a compound.<\/div>\n            <\/div>\n\n            <div class=\"ols-aqa312emf-spec-row ols-aqa312emf-spec-row--light\">\n              <div class=\"ols-aqa312emf-spec-code\">MF<\/div>\n              <div class=\"ols-aqa312emf-spec-text\">Molecular formula is the actual number of atoms of each element in a compound.<\/div>\n            <\/div>\n\n            <div class=\"ols-aqa312emf-spec-row ols-aqa312emf-spec-row--light\">\n              <div class=\"ols-aqa312emf-spec-code\">Link<\/div>\n              <div class=\"ols-aqa312emf-spec-text\">The relationship between empirical formula and molecular formula.<\/div>\n            <\/div>\n\n            <div class=\"ols-aqa312emf-spec-row ols-aqa312emf-spec-row--mid\">\n              <div class=\"ols-aqa312emf-spec-code ols-aqa312emf-spec-code--mid\">Skills<\/div>\n              <div class=\"ols-aqa312emf-spec-text\">Students should be able to:\n                <div class=\"ols-aqa312emf-spec-sub-list\">\n                  <div class=\"ols-aqa312emf-spec-sub-row\">\n                    <div class=\"ols-aqa312emf-spec-sub-code\">1<\/div>\n                    <div class=\"ols-aqa312emf-spec-sub-text\">calculate empirical formula from data giving composition by mass or percentage by mass<\/div>\n                  <\/div>\n                  <div class=\"ols-aqa312emf-spec-sub-row\">\n                    <div class=\"ols-aqa312emf-spec-sub-code\">2<\/div>\n                    <div class=\"ols-aqa312emf-spec-sub-text\">calculate molecular formula from the empirical formula and relative molecular mass.<\/div>\n                  <\/div>\n                <\/div>\n              <\/div>\n            <\/div>\n          <\/div>\n        <\/div>\n      <\/div>\n\n      <!-- MOBILE SPECIFICATION -->\n      <div class=\"ols-aqa312emf-spec-mobile\">\n        <div class=\"ols-aqa312emf-spec-wrap\">\n          <div class=\"ols-aqa312emf-spec-pill\">Specification Coverage<\/div>\n          <h2 class=\"ols-aqa312emf-spec-heading\">3.1.2.4 Empirical and Molecular Formula &#8211; AQA A Level Chemistry<\/h2>\n          <p class=\"ols-aqa312emf-spec-intro-text\">The following AQA specification points outline the knowledge and skills students are expected to demonstrate for empirical and molecular formulae.<\/p>\n\n          <h3 class=\"ols-aqa312emf-spec-group-title\">3.1.2.4 Empirical and molecular formula<\/h3>\n          <div class=\"ols-aqa312emf-spec-mob-rows\">\n            <div class=\"ols-aqa312emf-spec-mob-row ols-aqa312emf-spec-mob-row--light\">\n              <div class=\"ols-aqa312emf-spec-mob-code\">EF<\/div>\n              <div class=\"ols-aqa312emf-spec-mob-text\">Empirical formula is the simplest whole number ratio of atoms of each element in a compound.<\/div>\n            <\/div>\n\n            <div class=\"ols-aqa312emf-spec-mob-row ols-aqa312emf-spec-mob-row--light\">\n              <div class=\"ols-aqa312emf-spec-mob-code\">MF<\/div>\n              <div class=\"ols-aqa312emf-spec-mob-text\">Molecular formula is the actual number of atoms of each element in a compound.<\/div>\n            <\/div>\n\n            <div class=\"ols-aqa312emf-spec-mob-row ols-aqa312emf-spec-mob-row--light\">\n              <div class=\"ols-aqa312emf-spec-mob-code\">Link<\/div>\n              <div class=\"ols-aqa312emf-spec-mob-text\">The relationship between empirical formula and molecular formula.<\/div>\n            <\/div>\n\n            <div class=\"ols-aqa312emf-spec-mob-row ols-aqa312emf-spec-mob-row--mid\">\n              <div class=\"ols-aqa312emf-spec-mob-code ols-aqa312emf-spec-mob-code--mid\">Skills<\/div>\n              <div class=\"ols-aqa312emf-spec-mob-text\">Students should be able to:\n                <div class=\"ols-aqa312emf-spec-mob-sub-list\">\n                  <div class=\"ols-aqa312emf-spec-mob-sub-row\">\n                    <div class=\"ols-aqa312emf-spec-mob-sub-code\">1<\/div>\n                    <div class=\"ols-aqa312emf-spec-mob-sub-text\">calculate empirical formula from data giving composition by mass or percentage by mass<\/div>\n                  <\/div>\n                  <div class=\"ols-aqa312emf-spec-mob-sub-row\">\n                    <div class=\"ols-aqa312emf-spec-mob-sub-code\">2<\/div>\n                    <div class=\"ols-aqa312emf-spec-mob-sub-text\">calculate molecular formula from the empirical formula and relative molecular mass.<\/div>\n                  <\/div>\n                <\/div>\n              <\/div>\n            <\/div>\n          <\/div>\n        <\/div>\n      <\/div>\n\n    <\/div>\n  <\/section>\n\n<script type=\"application\/ld+json\">\n{\n  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Students learn the difference between empirical formula and molecular formula, how to calculate empirical formula from mass or percentage composition, and [&hellip;]<\/p>\n","protected":false},"author":12,"featured_media":0,"parent":5272,"menu_order":2,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-5275","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/pages\/5275","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/users\/12"}],"replies":[{"embeddable":true,"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/comments?post=5275"}],"version-history":[{"count":0,"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/pages\/5275\/revisions"}],"up":[{"embeddable":true,"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/pages\/5272"}],"wp:attachment":[{"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/media?parent=5275"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}