{"id":8071,"date":"2026-09-15T08:24:11","date_gmt":"2026-09-15T07:24:11","guid":{"rendered":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-2-atoms-molecules-and-stoichiometry\/"},"modified":"2026-09-15T08:35:23","modified_gmt":"2026-09-15T07:35:23","slug":"topic-2-atoms-molecules-and-stoichiometry","status":"publish","type":"page","link":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-2-atoms-molecules-and-stoichiometry\/","title":{"rendered":"Topic 2 Atoms, Molecules and Stoichiometry"},"content":{"rendered":"\n<div class=\"ols-cie2-page\">\n\n  <aside class=\"ols-sidebar\">\n  <div class=\"ols-sidebar-header\">\n    <h3>Revision Notes<\/h3>\n    <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  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linear-gradient(135deg, #78350f 0%, #d97706 55%, #fcd34d 100%); }\n    .ols-cie2-visual--polymer { background: linear-gradient(135deg, #064e3b 0%, #059669 55%, #6ee7b7 100%); }\n    .ols-cie2-visual--waste { background: linear-gradient(135deg, #334155 0%, #64748b 55%, #cbd5e1 100%); }\n    .ols-cie2-visual--alkane { background: linear-gradient(135deg, #1f2937 0%, #4b5563 55%, #9ca3af 100%); }\n    .ols-cie2-visual--naming { background: linear-gradient(135deg, #0f766e 0%, #14b8a6 55%, #99f6e4 100%); }\n    .ols-cie2-card--soon { opacity: 0.62; cursor: default; }\n    .ols-cie2-card-status--soon { background: #e5e7eb; color: #374151; }\n<\/style>\n\n  <!-- BREADCRUMB BAR -->\n  <div class=\"ols-cie2-breadcrumb-bar\">\n    <div class=\"ols-cie2-container\">\n      <nav class=\"ols-cie2-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\/cie\/\">Cambridge International (CIE)<\/a> \/\n          <span>Topic 2 Atoms, Molecules and Stoichiometry<\/span>\n        <\/nav>\n    <\/div>\n  <\/div>\n\n  <!-- INTRO -->\n  <section class=\"ols-cie2-intro\">\n    <div class=\"ols-cie2-container\">\n      <div class=\"ols-cie2-intro-inner\">\n        <div>\n          <div class=\"ols-cie2-eyebrow\">Cambridge International AS Level Chemistry<\/div>\n          <h1>Topic 2<br>Atoms, Molecules and Stoichiometry<\/h1>\n          <div class=\"ols-cie2-accent-bar\"><\/div>\n          <p class=\"ols-cie2-intro-lead\">Topic 2 covers relative masses and the mole, the formulae of compounds and balanced equations, empirical and molecular formulae, and calculations using the mole concept with masses, gas volumes and solutions. These pages cover all four parts; the extra named ions, hydrated salts and limiting reagents follow with the supplementary set.<\/p>\n        <\/div>\n        <div class=\"ols-cie2-info-grid\">\n          <div class=\"ols-cie2-info-card\"><div class=\"ols-cie2-info-card-label\">Exam Papers<\/div><div class=\"ols-cie2-info-card-value\">Papers 1 &amp; 2<\/div><div class=\"ols-cie2-info-card-sub\">9701\/1 and 9701\/2 (AS Level)<\/div><\/div>\n          <div class=\"ols-cie2-info-card\"><div class=\"ols-cie2-info-card-label\">Learning Outcomes<\/div><div class=\"ols-cie2-info-card-value\">2.1.1 &#8211; 2.4.1<\/div><div class=\"ols-cie2-info-card-sub\">4 parts<\/div><\/div>\n          <div class=\"ols-cie2-info-card\"><div class=\"ols-cie2-info-card-label\">Topic Parts<\/div><div class=\"ols-cie2-info-card-value\">4 of 4 live<\/div><div class=\"ols-cie2-info-card-sub\">2.1, 2.2, 2.3, 2.4<\/div><\/div>\n          <div class=\"ols-cie2-info-card\"><div class=\"ols-cie2-info-card-label\">Exam Board<\/div><div class=\"ols-cie2-info-card-value\">Cambridge<\/div><div class=\"ols-cie2-info-card-sub\">CIE 9701 (2025-2027)<\/div><\/div>\n        <\/div>\n      <\/div>\n    <\/div>\n  <\/section>\n\n  <!-- TOPIC CARDS -->\n  <section class=\"ols-cie2-topics\">\n    <div class=\"ols-cie2-container\">\n      <div class=\"ols-cie2-section-header\">\n        <h2 class=\"ols-cie2-section-title\">Revision Notes<\/h2>\n        <p class=\"ols-cie2-section-sub\">Work through each part of Cambridge Topic 2 in a structured sequence.<\/p>\n      <\/div>\n      <div class=\"ols-cie2-cards-grid\">\n        <!-- Card 1: 2.1 \/ 2.2 Atoms, Elements and Molecules -->\n        <a class=\"ols-cie2-card ols-cie2-card--available\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-2-atoms-molecules-and-stoichiometry\/atoms-elements-and-molecules\/\">\n          <div class=\"ols-cie2-card-img-wrap\">\n            <div class=\"ols-cie2-visual ols-cie2-visual--ionic\">\n              <div class=\"ols-cie2-visual-panel\">\n                <div class=\"ols-cie2-visual-kicker\">Foundations<\/div>\n                <div class=\"ols-cie2-visual-main\">Atoms, Elements<br>and Molecules<\/div>\n                <div class=\"ols-cie2-config-line\" aria-hidden=\"true\"><span>M\u1d63  L = 6.02\u00d710\u00b2\u00b3<\/span><\/div>\n              <\/div>\n            <\/div>\n            <div class=\"ols-cie2-card-num\">1<\/div>\n          <\/div>\n          <div class=\"ols-cie2-card-body\">\n            <p class=\"ols-cie2-card-title\">2.1 \/ 2.2 Atoms, Elements and Molecules<\/p>\n            <p class=\"ols-cie2-card-desc\">Relative atomic, molecular and formula mass, molar mass, the mole and the Avogadro constant (2.1, 2.2).<\/p>\n            <span class=\"ols-cie2-card-cta\">Start revising<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><\/span>\n          <\/div>\n        <\/a>\n\n        <a class=\"ols-cie2-card ols-cie2-card--available\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-2-atoms-molecules-and-stoichiometry\/ions-and-ionic-formulae\/\">\n          <div class=\"ols-cie2-card-img-wrap\">\n            <div class=\"ols-cie2-visual ols-cie2-visual--ionic\">\n              <div class=\"ols-cie2-visual-panel\">\n                <div class=\"ols-cie2-visual-kicker\">Formulae<\/div>\n                <div class=\"ols-cie2-visual-main\">Ions and<br>Ionic Formulae<\/div>\n                <div class=\"ols-cie2-config-line\" aria-hidden=\"true\"><span>Fe\u2082(SO\u2084)\u2083<\/span><\/div>\n              <\/div>\n            <\/div>\n            <div class=\"ols-cie2-card-num\">2<\/div>\n          <\/div>\n          <div class=\"ols-cie2-card-body\">\n            <p class=\"ols-cie2-card-title\">2.3 Ions and Ionic Formulae<\/p>\n            <p class=\"ols-cie2-card-desc\">Ion charges from the Periodic Table, the nine named ions, Roman-numeral oxidation numbers and constructing ionic formulae (2.3.1).<\/p>\n            <span class=\"ols-cie2-card-cta\">Start revising<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><\/span>\n          <\/div>\n        <\/a>\n\n        <a class=\"ols-cie2-card ols-cie2-card--available\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-2-atoms-molecules-and-stoichiometry\/hydrated-salts-and-water-of-crystallisation\/\">\n          <div class=\"ols-cie2-card-img-wrap\">\n            <div class=\"ols-cie2-visual ols-cie2-visual--ionic\">\n              <div class=\"ols-cie2-visual-panel\">\n                <div class=\"ols-cie2-visual-kicker\">Water of crystallisation<\/div>\n                <div class=\"ols-cie2-visual-main\">Hydrated<br>Salts<\/div>\n                <div class=\"ols-cie2-config-line\" aria-hidden=\"true\"><span>CuSO\u2084\u00b75H\u2082O<\/span><\/div>\n              <\/div>\n            <\/div>\n            <div class=\"ols-cie2-card-num\">3<\/div>\n          <\/div>\n          <div class=\"ols-cie2-card-body\">\n            <p class=\"ols-cie2-card-title\">2.3 Hydrated Salts and Water of Crystallisation<\/p>\n            <p class=\"ols-cie2-card-desc\">Anhydrous and hydrated salts, water of crystallisation and finding the degree of hydration (2.3.4).<\/p>\n            <span class=\"ols-cie2-card-cta\">Start revising<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><\/span>\n          <\/div>\n        <\/a>\n\n        <!-- Card 2: 2.3 Equations and Reaction Types -->\n        <a class=\"ols-cie2-card ols-cie2-card--available\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-2-atoms-molecules-and-stoichiometry\/equations-and-reaction-types\/\">\n          <div class=\"ols-cie2-card-img-wrap\">\n            <div class=\"ols-cie2-visual ols-cie2-visual--covalent\">\n              <div class=\"ols-cie2-visual-panel\">\n                <div class=\"ols-cie2-visual-kicker\">Equations<\/div>\n                <div class=\"ols-cie2-visual-main\">Equations and<br>Reaction Types<\/div>\n                <div class=\"ols-cie2-config-line\" aria-hidden=\"true\"><span>Na\u2082CO\u2083 + 2HCl<\/span><\/div>\n              <\/div>\n            <\/div>\n            <div class=\"ols-cie2-card-num\">4<\/div>\n          <\/div>\n          <div class=\"ols-cie2-card-body\">\n            <p class=\"ols-cie2-card-title\">2.3 Equations and Reaction Types<\/p>\n            <p class=\"ols-cie2-card-desc\">Balanced full and ionic equations with state symbols, and the typical reactions of acids (2.3.2).<\/p>\n            <span class=\"ols-cie2-card-cta\">Start revising<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><\/span>\n          <\/div>\n        <\/a>\n\n        <!-- Card 3: 2.3 Empirical and Molecular Formulae -->\n        <a class=\"ols-cie2-card ols-cie2-card--available\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-2-atoms-molecules-and-stoichiometry\/empirical-and-molecular-formulae\/\">\n          <div class=\"ols-cie2-card-img-wrap\">\n            <div class=\"ols-cie2-visual ols-cie2-visual--shapes\">\n              <div class=\"ols-cie2-visual-panel\">\n                <div class=\"ols-cie2-visual-kicker\">Formulae<\/div>\n                <div class=\"ols-cie2-visual-main\">Empirical and<br>Molecular<\/div>\n                <div class=\"ols-cie2-config-line\" aria-hidden=\"true\"><span>CH\u2082O \u2192 C\u2086H\u2081\u2082O\u2086<\/span><\/div>\n              <\/div>\n            <\/div>\n            <div class=\"ols-cie2-card-num\">5<\/div>\n          <\/div>\n          <div class=\"ols-cie2-card-body\">\n            <p class=\"ols-cie2-card-title\">2.3 Empirical and Molecular Formulae<\/p>\n            <p class=\"ols-cie2-card-desc\">Empirical formulae from data and molecular formulae from M\u1d63 (2.3.3, 2.3.5).<\/p>\n            <span class=\"ols-cie2-card-cta\">Start revising<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><\/span>\n          <\/div>\n        <\/a>\n\n        <!-- Card 4: 2.4 Mole Calculations -->\n        <a class=\"ols-cie2-card ols-cie2-card--available\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-2-atoms-molecules-and-stoichiometry\/mole-calculations\/\">\n          <div class=\"ols-cie2-card-img-wrap\">\n            <div class=\"ols-cie2-visual ols-cie2-visual--metallic\">\n              <div class=\"ols-cie2-visual-panel\">\n                <div class=\"ols-cie2-visual-kicker\">Calculations<\/div>\n                <div class=\"ols-cie2-visual-main\">Mole<br>Calculations<\/div>\n                <div class=\"ols-cie2-config-line\" aria-hidden=\"true\"><span>n = m \/ M<\/span><\/div>\n              <\/div>\n            <\/div>\n            <div class=\"ols-cie2-card-num\">6<\/div>\n          <\/div>\n          <div class=\"ols-cie2-card-body\">\n            <p class=\"ols-cie2-card-title\">2.4 Mole Calculations<\/p>\n            <p class=\"ols-cie2-card-desc\">Reacting masses, percentage yield, atom economy and stoichiometric relationships (2.4.1 (a), (e)).<\/p>\n            <span class=\"ols-cie2-card-cta\">Start revising<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><\/span>\n          <\/div>\n        <\/a>\n\n        <!-- Card 5: 2.4 Solutions and Gases -->\n        <a class=\"ols-cie2-card ols-cie2-card--available\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-2-atoms-molecules-and-stoichiometry\/calculations-with-solutions-and-gases\/\">\n          <div class=\"ols-cie2-card-img-wrap\">\n            <div class=\"ols-cie2-visual ols-cie2-visual--forces\">\n              <div class=\"ols-cie2-visual-panel\">\n                <div class=\"ols-cie2-visual-kicker\">Gases and solutions<\/div>\n                <div class=\"ols-cie2-visual-main\">Solutions<br>and Gases<\/div>\n                <div class=\"ols-cie2-config-line\" aria-hidden=\"true\"><span>pV = nRT<\/span><\/div>\n              <\/div>\n            <\/div>\n            <div class=\"ols-cie2-card-num\">7<\/div>\n          <\/div>\n          <div class=\"ols-cie2-card-body\">\n            <p class=\"ols-cie2-card-title\">2.4 Solutions and Gases<\/p>\n            <p class=\"ols-cie2-card-desc\">Volumes of gases and volumes and concentrations of solutions (2.4.1 (b), (c)).<\/p>\n            <span class=\"ols-cie2-card-cta\">Start revising<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><\/span>\n          <\/div>\n        <\/a>\n\n      \n\n      <\/div>\n    <\/div>\n  <\/section>\n\n  <!-- SPECIFICATION -->\n  <section class=\"ols-cie2-spec-section\">\n    <div class=\"ols-cie2-container\">\n      <div class=\"ols-cie2-spec-wrap\">\n        <div class=\"ols-cie2-spec-pill\">Specification Coverage<\/div>\n        <h2 class=\"ols-cie2-spec-heading\">Topic 2 Atoms, Molecules and Stoichiometry &#8211; Cambridge International AS Level Chemistry<\/h2>\n        <p class=\"ols-cie2-spec-intro-text\">The following Cambridge learning outcomes state what candidates should be able to do for Topic 2. Wording is taken from the Cambridge International AS &amp; A Level Chemistry 9701 syllabus (2025-2027).<\/p>\n\n        <h3 class=\"ols-cie2-spec-group-title\">2.1 Relative masses of atoms and molecules<\/h3>\n<div class=\"ols-cie2-spec-rows\">\n<div class=\"ols-cie2-spec-row ols-cie2-spec-row--light\"><div class=\"ols-cie2-spec-code\">2.1.1<\/div><div class=\"ols-cie2-spec-text\">define the unified atomic mass unit as one twelfth of the mass of a carbon-12 atom<\/div><\/div>\n<div class=\"ols-cie2-spec-row ols-cie2-spec-row--mid\"><div class=\"ols-cie2-spec-code ols-cie2-spec-code--mid\">2.1.2<\/div><div class=\"ols-cie2-spec-text\">define relative atomic mass, Ar, relative isotopic mass, relative molecular mass, Mr, and relative formula mass in terms of the unified atomic mass unit<\/div><\/div>\n<\/div>\n<h3 class=\"ols-cie2-spec-group-title\">2.2 The mole and the Avogadro constant<\/h3>\n<div class=\"ols-cie2-spec-rows\">\n<div class=\"ols-cie2-spec-row ols-cie2-spec-row--light\"><div class=\"ols-cie2-spec-code\">2.2.1<\/div><div class=\"ols-cie2-spec-text\">define and use the term mole in terms of the Avogadro constant<\/div><\/div>\n<\/div>\n<h3 class=\"ols-cie2-spec-group-title\">2.3 Formulas<\/h3>\n<div class=\"ols-cie2-spec-rows\">\n<div class=\"ols-cie2-spec-row ols-cie2-spec-row--mid\"><div class=\"ols-cie2-spec-code ols-cie2-spec-code--mid\">2.3.1<\/div><div class=\"ols-cie2-spec-text\">write formulas of ionic compounds from ionic charges and oxidation numbers (shown by a Roman numeral), including:<div class=\"ols-cie2-spec-sub-list\"><div class=\"ols-cie2-spec-sub-row\"><div class=\"ols-cie2-spec-sub-code\">(a)<\/div><div class=\"ols-cie2-spec-sub-text\">the prediction of ionic charge from the position of an element in the Periodic Table<\/div><\/div><div class=\"ols-cie2-spec-sub-row\"><div class=\"ols-cie2-spec-sub-code\">(b)<\/div><div class=\"ols-cie2-spec-sub-text\">recall of the names and formulas for the following ions: NO3\u2013, CO32\u2013, SO42\u2013, OH\u2013, NH4+, Zn2+, Ag+, HCO3\u2013, PO43\u2013<\/div><\/div><\/div><\/div><\/div>\n<div class=\"ols-cie2-spec-row ols-cie2-spec-row--light\"><div class=\"ols-cie2-spec-code\">2.3.2<\/div><div class=\"ols-cie2-spec-text\"><div class=\"ols-cie2-spec-sub-list\"><div class=\"ols-cie2-spec-sub-row\"><div class=\"ols-cie2-spec-sub-code\">(a)<\/div><div class=\"ols-cie2-spec-sub-text\">write and construct equations (which should be balanced), including ionic equations (which should not include spectator ions)<\/div><\/div><div class=\"ols-cie2-spec-sub-row\"><div class=\"ols-cie2-spec-sub-code\">(b)<\/div><div class=\"ols-cie2-spec-sub-text\">use appropriate state symbols in equations<\/div><\/div><\/div><\/div><\/div>\n<div class=\"ols-cie2-spec-row ols-cie2-spec-row--mid\"><div class=\"ols-cie2-spec-code ols-cie2-spec-code--mid\">2.3.3<\/div><div class=\"ols-cie2-spec-text\">define and use the terms empirical and molecular formula<\/div><\/div>\n<div class=\"ols-cie2-spec-row ols-cie2-spec-row--light\"><div class=\"ols-cie2-spec-code\">2.3.4<\/div><div class=\"ols-cie2-spec-text\">understand and use the terms anhydrous, hydrated and water of crystallisation<\/div><\/div>\n<div class=\"ols-cie2-spec-row ols-cie2-spec-row--mid\"><div class=\"ols-cie2-spec-code ols-cie2-spec-code--mid\">2.3.5<\/div><div class=\"ols-cie2-spec-text\">calculate empirical and molecular formulas, using given data<\/div><\/div>\n<\/div>\n<h3 class=\"ols-cie2-spec-group-title\">2.4 Reacting masses and volumes (of solutions and gases)<\/h3>\n<div class=\"ols-cie2-spec-rows\">\n<div class=\"ols-cie2-spec-row ols-cie2-spec-row--light\"><div class=\"ols-cie2-spec-code\">2.4.1<\/div><div class=\"ols-cie2-spec-text\">perform calculations including use of the mole concept, involving:<div class=\"ols-cie2-spec-sub-list\"><div class=\"ols-cie2-spec-sub-row\"><div class=\"ols-cie2-spec-sub-code\">(a)<\/div><div class=\"ols-cie2-spec-sub-text\">reacting masses (from formulas and equations) including percentage yield calculations<\/div><\/div><div class=\"ols-cie2-spec-sub-row\"><div class=\"ols-cie2-spec-sub-code\">(b)<\/div><div class=\"ols-cie2-spec-sub-text\">volumes of gases (e.g. in the burning of hydrocarbons)<\/div><\/div><div class=\"ols-cie2-spec-sub-row\"><div class=\"ols-cie2-spec-sub-code\">(c)<\/div><div class=\"ols-cie2-spec-sub-text\">volumes and concentrations of solutions<\/div><\/div><div class=\"ols-cie2-spec-sub-row\"><div class=\"ols-cie2-spec-sub-code\">(d)<\/div><div class=\"ols-cie2-spec-sub-text\">limiting reagent and excess reagent<\/div><\/div><div class=\"ols-cie2-spec-sub-row\"><div class=\"ols-cie2-spec-sub-code\">(e)<\/div><div class=\"ols-cie2-spec-sub-text\">deduce stoichiometric relationships from calculations such as those in 2.4.1(a)\u2013(d)<\/div><\/div><\/div><\/div><\/div>\n<\/div>\n      <\/div>\n    <\/div>\n  <\/section>\n\n<script 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