{"id":8048,"date":"2026-09-15T08:23:29","date_gmt":"2026-09-15T07:23:29","guid":{"rendered":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-1-2-compounds-formulae-and-equations\/"},"modified":"2026-09-15T08:35:16","modified_gmt":"2026-09-15T07:35:16","slug":"2-1-2-compounds-formulae-and-equations","status":"publish","type":"page","link":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-1-2-compounds-formulae-and-equations\/","title":{"rendered":"2.1.2 Compounds, Formulae and Equations"},"content":{"rendered":"\n<div class=\"ols-ocr212-page\">\n\n  <aside class=\"ols-sidebar\">\n  <div class=\"ols-sidebar-header\">\n    <h3>Revision Notes<\/h3>\n    <p>OCR A Level Chemistry A<\/p>\n  <\/div>\n  <div class=\"ols-topic-group\">\n    <h4>2.1.2 Compounds, Formulae and Equations<\/h4>\n    <ul class=\"ols-topic-list\">\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-1-2-compounds-formulae-and-equations\/\">Section overview<\/a><\/li>\n<li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-1-2-compounds-formulae-and-equations\/ions-and-ionic-formulae\/\">Ions and Ionic Formulae<\/a><\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-1-2-compounds-formulae-and-equations\/equations-and-reaction-types\/\">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\/ocr-a\/2-1-2-compounds-formulae-and-equations\/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\/ocr-a\/2-1-2-compounds-formulae-and-equations\/equations-and-reaction-types\/ionic-and-full-equations\/\">Ionic and Full Equations<\/a><\/li>\n          <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-1-4-acids\/typical-reactions-of-acids\/\">Typical Reactions of Acids<\/a><\/li>\n        <\/ul>\n      <\/li>\n    <\/ul>\n  <\/div>\n  <div class=\"ols-topic-group\">\n    <h4>Other OCR Sections<\/h4>\n    <ul class=\"ols-topic-list\">\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-1-1-atomic-structure-and-isotopes\/\">2.1.1 Atomic Structure and Isotopes<\/a><\/li>\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-1-3-amount-of-substance\/\">2.1.3 Amount of Substance<\/a><\/li>\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-1-4-acids\/\">2.1.4 Acids<\/a><\/li>\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-2-1-electron-structure\/\">2.2.1 Electron Structure<\/a><\/li>\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-2-2-bonding-and-structure\/\">2.2.2 Bonding and Structure<\/a><\/li>\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/3-1-1-periodicity\/\">3.1.1 Periodicity<\/a><\/li>\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/4-1-1-basic-concepts-of-organic-chemistry\/\">4.1.1 Basic Concepts of Organic Chemistry<\/a><\/li>\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/4-1-2-alkanes\/\">4.1.2 Alkanes<\/a><\/li>\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/4-1-3-alkenes\/\">4.1.3 Alkenes<\/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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.ols-ocr212-spec-wrap { padding: 24px 18px; border-radius: 20px; }\n      .ols-ocr212-info-grid { grid-template-columns: 1fr 1fr; }\n      .ols-ocr212-spec-row { flex-direction: column; }\n      .ols-ocr212-spec-code { flex: 0 0 auto; min-height: 34px; }\n    }\n  <\/style>\n\n  <!-- BREADCRUMB BAR -->\n  <div class=\"ols-ocr212-breadcrumb-bar\">\n    <div class=\"ols-ocr212-container\">\n      <nav class=\"ols-ocr212-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\/ocr-a\/\">OCR<\/a> \/\n        <span>2.1.2 Compounds, Formulae and Equations<\/span>\n      <\/nav>\n    <\/div>\n  <\/div>\n\n  <!-- INTRO -->\n  <section class=\"ols-ocr212-intro\">\n    <div class=\"ols-ocr212-container\">\n      <div class=\"ols-ocr212-intro-inner\">\n        <div>\n          <div class=\"ols-ocr212-eyebrow\">OCR A Level Chemistry A &#8211; Module 2 Foundations in Chemistry<\/div>\n          <h1>2.1.2<br>Compounds, Formulae and Equations<\/h1>\n          <div class=\"ols-ocr212-accent-bar\"><\/div>\n          <p class=\"ols-ocr212-intro-lead\">Section 2.1.2 covers writing the formulae of ionic compounds from ionic charges and constructing balanced full and ionic equations with state symbols, for reactions studied and for unfamiliar reactions. These pages cover the equations; the ionic formulae page follows with the supplementary set.<\/p>\n        <\/div>\n        <div class=\"ols-ocr212-info-grid\">\n          <div class=\"ols-ocr212-info-card\"><div class=\"ols-ocr212-info-card-label\">Exam Paper<\/div><div class=\"ols-ocr212-info-card-value\">Paper 1 &amp; 2<\/div><div class=\"ols-ocr212-info-card-sub\">H432\/01 and H432\/02<\/div><\/div>\n          <div class=\"ols-ocr212-info-card\"><div class=\"ols-ocr212-info-card-label\">Specification Points<\/div><div class=\"ols-ocr212-info-card-value\">2.1.2 (a) &#8211; (b)<\/div><div class=\"ols-ocr212-info-card-sub\">2 learning outcomes<\/div><\/div>\n          <div class=\"ols-ocr212-info-card\"><div class=\"ols-ocr212-info-card-label\">Topic Parts<\/div><div class=\"ols-ocr212-info-card-value\">1 of 2 live<\/div><div class=\"ols-ocr212-info-card-sub\">Equations and Reaction Types<\/div><\/div>\n          <div class=\"ols-ocr212-info-card\"><div class=\"ols-ocr212-info-card-label\">Exam Board<\/div><div class=\"ols-ocr212-info-card-value\">OCR A<\/div><div class=\"ols-ocr212-info-card-sub\">H432 (2015 onwards)<\/div><\/div>\n        <\/div>\n      <\/div>\n    <\/div>\n  <\/section>\n\n  <!-- TOPIC CARDS -->\n  <section class=\"ols-ocr212-topics\">\n    <div class=\"ols-ocr212-container\">\n      <div class=\"ols-ocr212-section-header\">\n        <h2 class=\"ols-ocr212-section-title\">Revision Notes<\/h2>\n        <p class=\"ols-ocr212-section-sub\">Work through 2.1.2 in a structured sequence.<\/p>\n      <\/div>\n      <div class=\"ols-ocr212-cards-grid\">\n        <!-- Card 1: Equations and Reaction Types -->\n        <a class=\"ols-ocr212-card ols-ocr212-card--available\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-1-2-compounds-formulae-and-equations\/equations-and-reaction-types\/\">\n          <div class=\"ols-ocr212-card-img-wrap\">\n            <div class=\"ols-ocr212-visual ols-ocr212-visual--covalent\">\n              <div class=\"ols-ocr212-visual-panel\">\n                <div class=\"ols-ocr212-visual-kicker\">Equations<\/div>\n                <div class=\"ols-ocr212-visual-main\">Equations and<br>Reaction Types<\/div>\n                <div class=\"ols-ocr212-config-line\" aria-hidden=\"true\"><span>Na\u2082CO\u2083 + 2HCl<\/span><\/div>\n              <\/div>\n            <\/div>\n            <div class=\"ols-ocr212-card-num\">1<\/div>\n          <\/div>\n          <div class=\"ols-ocr212-card-body\">\n            <p class=\"ols-ocr212-card-title\">Equations and Reaction Types<\/p>\n            <p class=\"ols-ocr212-card-desc\">Writing and balancing full equations with state symbols, ionic equations, and the typical reactions of acids (2.1.2 (b)).<\/p>\n            <span class=\"ols-ocr212-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-ocr212-card ols-ocr212-card--available\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-1-2-compounds-formulae-and-equations\/ions-and-ionic-formulae\/\">\n          <div class=\"ols-ocr212-card-img-wrap\">\n            <div class=\"ols-ocr212-visual ols-ocr212-visual--covalent\">\n              <div class=\"ols-ocr212-visual-panel\">\n                <div class=\"ols-ocr212-visual-kicker\">Formulae<\/div>\n                <div class=\"ols-ocr212-visual-main\">Ions and<br>Ionic Formulae<\/div>\n                <div class=\"ols-ocr212-config-line\" aria-hidden=\"true\"><span>Zn\u00b2\u207a SO\u2084\u00b2\u207b \u2192 ZnSO\u2084<\/span><\/div>\n              <\/div>\n            <\/div>\n            <div class=\"ols-ocr212-card-num\">2<\/div>\n          <\/div>\n          <div class=\"ols-ocr212-card-body\">\n            <p class=\"ols-ocr212-card-title\">Ions and Ionic Formulae<\/p>\n            <p class=\"ols-ocr212-card-desc\">Predicting ion charges from the Periodic Table, the seven named ions and constructing ionic formulae (2.1.2 (a)).<\/p>\n            <span class=\"ols-ocr212-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      <\/div>\n    <\/div>\n  <\/section>\n  <!-- SPECIFICATION -->\n  <section class=\"ols-ocr212-spec-section\">\n    <div class=\"ols-ocr212-container\">\n      <div class=\"ols-ocr212-spec-wrap\">\n        <div class=\"ols-ocr212-spec-pill\">Specification Coverage<\/div>\n        <h2 class=\"ols-ocr212-spec-heading\">2.1.2 Compounds, Formulae and Equations &#8211; OCR A Level Chemistry A<\/h2>\n        <p class=\"ols-ocr212-spec-intro-text\">The following OCR A learning outcomes state what candidates should be able to do. Wording is taken from the OCR A Level Chemistry A (H432) specification.<\/p>\n        <h3 class=\"ols-ocr212-spec-group-title\">2.1.2 Compounds, Formulae and Equations<\/h3>\n        <div class=\"ols-ocr212-spec-rows\">\n          <div class=\"ols-ocr212-spec-row ols-ocr212-spec-row--light\">\n<div class=\"ols-ocr212-spec-code\">2.1.2(a)<\/div>\n<div class=\"ols-ocr212-spec-text\"><strong>Formulae of ionic compounds<\/strong><div class=\"ols-ocr212-spec-sub-list\"><div class=\"ols-ocr212-spec-sub-row\"><div class=\"ols-ocr212-spec-sub-code\"><\/div><div class=\"ols-ocr212-spec-sub-text\">the writing of formulae of ionic compounds from ionic charges<\/div><\/div><div class=\"ols-ocr212-spec-sub-row\"><div class=\"ols-ocr212-spec-sub-code\">i<\/div><div class=\"ols-ocr212-spec-sub-text\">prediction of ionic charge from the position of an element in the periodic table<\/div><\/div><div class=\"ols-ocr212-spec-sub-row\"><div class=\"ols-ocr212-spec-sub-code\">ii)-a<\/div><div class=\"ols-ocr212-spec-sub-text\">recall of the name and formula for the nitrate ion, NO3\u2013<\/div><\/div><div class=\"ols-ocr212-spec-sub-row\"><div class=\"ols-ocr212-spec-sub-code\">ii)-b<\/div><div class=\"ols-ocr212-spec-sub-text\">recall of the name and formula for the carbonate ion, CO32\u2013<\/div><\/div><div class=\"ols-ocr212-spec-sub-row\"><div class=\"ols-ocr212-spec-sub-code\">ii)-c<\/div><div class=\"ols-ocr212-spec-sub-text\">recall of the name and formula for the sulfate ion, SO42\u2013<\/div><\/div><div class=\"ols-ocr212-spec-sub-row\"><div class=\"ols-ocr212-spec-sub-code\">ii)-d<\/div><div class=\"ols-ocr212-spec-sub-text\">recall of the name and formula for the hydroxide ion, OH\u2013<\/div><\/div><div class=\"ols-ocr212-spec-sub-row\"><div class=\"ols-ocr212-spec-sub-code\">ii)-e<\/div><div class=\"ols-ocr212-spec-sub-text\">recall of the name and formula for the ammonium ion, NH4+<\/div><\/div><div class=\"ols-ocr212-spec-sub-row\"><div class=\"ols-ocr212-spec-sub-code\">ii)-f<\/div><div class=\"ols-ocr212-spec-sub-text\">recall of the name and formula for the zinc ion, Zn2+<\/div><\/div><div class=\"ols-ocr212-spec-sub-row\"><div class=\"ols-ocr212-spec-sub-code\">ii)-g<\/div><div class=\"ols-ocr212-spec-sub-text\">recall of the name and formula for the silver ion, Ag+<\/div><\/div><\/div><\/div>\n<\/div>\n          <div class=\"ols-ocr212-spec-row ols-ocr212-spec-row--mid\">\n<div class=\"ols-ocr212-spec-code ols-ocr212-spec-code--mid\">2.1.2(b)<\/div>\n<div class=\"ols-ocr212-spec-text\"><strong>Balanced equations<\/strong><div class=\"ols-ocr212-spec-sub-list\"><div class=\"ols-ocr212-spec-sub-row\"><div class=\"ols-ocr212-spec-sub-code\">i<\/div><div class=\"ols-ocr212-spec-sub-text\">construction of balanced chemical equations, including state symbols, for reactions studied<\/div><\/div><div class=\"ols-ocr212-spec-sub-row\"><div class=\"ols-ocr212-spec-sub-code\">ii<\/div><div class=\"ols-ocr212-spec-sub-text\">construction of balanced ionic equations, including state symbols, for reactions studied<\/div><\/div><div class=\"ols-ocr212-spec-sub-row\"><div class=\"ols-ocr212-spec-sub-code\">iii<\/div><div class=\"ols-ocr212-spec-sub-text\">construction of balanced chemical equations (including ionic equations), including state symbols, for unfamiliar reactions given appropriate information<\/div><\/div><\/div><\/div>\n<\/div>\n        <\/div>\n      <\/div>\n    <\/div>\n  <\/section>\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\/ocr-a\/2-1-2-compounds-formulae-and-equations\/#webpage\",\n      \"url\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-1-2-compounds-formulae-and-equations\/\",\n      \"name\": \"2.1.2 Compounds, Formulae and Equations - 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