{"id":10554,"date":"2026-09-26T11:34:24","date_gmt":"2026-09-26T10:34:24","guid":{"rendered":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-1-5-redox\/"},"modified":"2026-09-26T11:34:24","modified_gmt":"2026-09-26T10:34:24","slug":"2-1-5-redox","status":"publish","type":"page","link":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-1-5-redox\/","title":{"rendered":"2.1.5 Redox"},"content":{"rendered":"\n<div class=\"ols-ocr215-page\">\n\n  <aside class=\"ols-sidebar\">\n  <div class=\"ols-sidebar-header\">\n    <h3>Revision Notes<\/h3>\n    <p>A Level Chemistry<\/p>\n  <\/div>\n\n  <div class=\"ols-topic-group\">\n    <h4>2.1.5 Redox<\/h4>\n\n    <ul class=\"ols-topic-list\">\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-1-5-redox\/\">2.1.5 Overview<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-1-5-redox\/oxidation-numbers\/\">Oxidation Numbers<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-1-5-redox\/electron-transfer-and-half-equations\/\">Electron Transfer and Half-Equations<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-1-5-redox\/disproportionation\/\">Disproportionation<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-1-5-redox\/redox-classification\/\">Redox Classification<\/a>\n      <\/li>\n    <\/ul>\n  <\/div>\n\n  <div class=\"ols-topic-group\">\n    <h4>Other Sections<\/h4>\n\n    <ul class=\"ols-topic-list\">\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/3-1-2-group-2\/\">3.1.2 Group 2<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/3-1-3-the-halogens\/\">3.1.3 The Halogens<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/3-1-4-qualitative-analysis\/\">3.1.4 Qualitative Analysis<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-1-4-acids\/\">2.1.4 Acids<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/3-1-1-periodicity\/\">3.1.1 Periodicity<\/a>\n      <\/li>\n      <li>\n        <a 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linear-gradient(135deg, #fdf4ff 0%, #d8b4fe 45%, #7e22ce 100%); }\n  <\/style>\n\n  <!-- BREADCRUMB BAR -->\n  <div class=\"ols-ocr215-breadcrumb-bar\">\n    <div class=\"ols-ocr215-container\">\n      <nav class=\"ols-ocr215-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>2.1.5 Redox<\/span>\n        <\/nav>\n    <\/div>\n  <\/div>\n\n  <!-- INTRO -->\n  <section class=\"ols-ocr215-intro\">\n    <div class=\"ols-ocr215-container\">\n      <div class=\"ols-ocr215-intro-inner\">\n        <div>\n          <div class=\"ols-ocr215-eyebrow\">OCR A Level Chemistry A<\/div>\n          <h1>2.1.5<br>Redox<\/h1>\n          <div class=\"ols-ocr215-accent-bar\"><\/div>\n          <p class=\"ols-ocr215-intro-lead\">Section 2.1.5 covers the rules for oxidation numbers in elements, compounds and ions, writing formulae from oxidation numbers and using Roman numerals, oxidation and reduction as electron transfer and as changes in oxidation number, the redox reactions of metals with acids, and interpreting unfamiliar redox equations. Disproportionation is revision support here and is examined in 3.1.3 for chlorine.<\/p>\n        <\/div>\n        <div class=\"ols-ocr215-info-grid\">\n          <div class=\"ols-ocr215-info-card\"><div class=\"ols-ocr215-info-card-label\">Exam Paper<\/div><div class=\"ols-ocr215-info-card-value\">Paper 1 &amp; 3<\/div><div class=\"ols-ocr215-info-card-sub\">H432\/01 and H432\/03<\/div><\/div>\n          <div class=\"ols-ocr215-info-card\"><div class=\"ols-ocr215-info-card-label\">Specification Points<\/div><div class=\"ols-ocr215-info-card-value\">2.1.5 (a) &#8211; (f)<\/div><div class=\"ols-ocr215-info-card-sub\">6 learning outcomes<\/div><\/div>\n          <div class=\"ols-ocr215-info-card\"><div class=\"ols-ocr215-info-card-label\">Topic Parts<\/div><div class=\"ols-ocr215-info-card-value\">4 pages<\/div><div class=\"ols-ocr215-info-card-sub\">Revision notes available<\/div><\/div>\n          <div class=\"ols-ocr215-info-card\"><div class=\"ols-ocr215-info-card-label\">Exam Board<\/div><div class=\"ols-ocr215-info-card-value\">OCR A<\/div><div class=\"ols-ocr215-info-card-sub\">H432 (2015 onwards)<\/div><\/div>\n        <\/div>\n      <\/div>\n    <\/div>\n  <\/section>\n\n  <!-- TOPIC CARDS -->\n  <section class=\"ols-ocr215-topics\">\n    <div class=\"ols-ocr215-container\">\n      <div class=\"ols-ocr215-section-header\">\n        <h2 class=\"ols-ocr215-section-title\">Revision Notes<\/h2>\n        <p class=\"ols-ocr215-section-sub\">Work through 2.1.5 Redox in a structured sequence.<\/p>\n      <\/div>\n      <div class=\"ols-ocr215-cards-grid\">\n\n        <!-- Card 1: Oxidation Numbers -->\n        <a class=\"ols-ocr215-card ols-ocr215-card--available\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-1-5-redox\/oxidation-numbers\/\">\n          <div class=\"ols-ocr215-card-img-wrap\">\n            <div class=\"ols-ocr215-visual ols-ocr215-visual--ox\">\n              <div class=\"ols-ocr215-visual-panel\">\n                <div class=\"ols-ocr215-visual-kicker\">Bookkeeping<\/div>\n                <div class=\"ols-ocr215-visual-main\">Oxidation<br>Numbers<\/div>\n                <div class=\"ols-ocr215-config-line\" aria-hidden=\"true\"><span>rules, ions, Roman numerals<\/span><\/div>\n              <\/div>\n            <\/div>\n            <div class=\"ols-ocr215-card-num\">1<\/div>\n            <span class=\"ols-ocr215-card-status ols-ocr215-card-status--available\">Available<\/span>\n          <\/div>\n          <div class=\"ols-ocr215-card-body\">\n            <p class=\"ols-ocr215-card-title\">Oxidation Numbers<\/p>\n            <p class=\"ols-ocr215-card-desc\">Oxidation numbers: the rules, calculating them in compounds, ions, peroxides and metal hydrides, Roman numerals and writing formulae.<\/p>\n            <span class=\"ols-ocr215-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: Electron Transfer and Half-Equations -->\n        <a class=\"ols-ocr215-card ols-ocr215-card--available\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-1-5-redox\/electron-transfer-and-half-equations\/\">\n          <div class=\"ols-ocr215-card-img-wrap\">\n            <div class=\"ols-ocr215-visual ols-ocr215-visual--et\">\n              <div class=\"ols-ocr215-visual-panel\">\n                <div class=\"ols-ocr215-visual-kicker\">OIL RIG<\/div>\n                <div class=\"ols-ocr215-visual-main\">Electron<br>Transfer<\/div>\n                <div class=\"ols-ocr215-config-line\" aria-hidden=\"true\"><span>half-equations and agents<\/span><\/div>\n              <\/div>\n            <\/div>\n            <div class=\"ols-ocr215-card-num\">2<\/div>\n            <span class=\"ols-ocr215-card-status ols-ocr215-card-status--available\">Available<\/span>\n          <\/div>\n          <div class=\"ols-ocr215-card-body\">\n            <p class=\"ols-ocr215-card-title\">Electron Transfer and Half-Equations<\/p>\n            <p class=\"ols-ocr215-card-desc\">Redox as electron transfer: oxidising and reducing agents, oxidation number changes, writing ionic half-equations and combining them into full ionic equations.<\/p>\n            <span class=\"ols-ocr215-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: Disproportionation -->\n        <a class=\"ols-ocr215-card ols-ocr215-card--available\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-1-5-redox\/disproportionation\/\">\n          <div class=\"ols-ocr215-card-img-wrap\">\n            <div class=\"ols-ocr215-visual ols-ocr215-visual--dp\">\n              <div class=\"ols-ocr215-visual-panel\">\n                <div class=\"ols-ocr215-visual-kicker\">Both ways at once<\/div>\n                <div class=\"ols-ocr215-visual-main\">Dispropor-<br>tionation<\/div>\n                <div class=\"ols-ocr215-config-line\" aria-hidden=\"true\"><span>Cl\u2082, H\u2082O\u2082, Cu\u207a<\/span><\/div>\n              <\/div>\n            <\/div>\n            <div class=\"ols-ocr215-card-num\">3<\/div>\n            <span class=\"ols-ocr215-card-status ols-ocr215-card-status--available\">Available<\/span>\n          <\/div>\n          <div class=\"ols-ocr215-card-body\">\n            <p class=\"ols-ocr215-card-title\">Disproportionation<\/p>\n            <p class=\"ols-ocr215-card-desc\">Disproportionation: recognising it with oxidation numbers, chlorine in water and alkali, hydrogen peroxide, copper(I) and which species cannot disproportionate.<\/p>\n            <span class=\"ols-ocr215-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: Redox Classification -->\n        <a class=\"ols-ocr215-card ols-ocr215-card--available\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-1-5-redox\/redox-classification\/\">\n          <div class=\"ols-ocr215-card-img-wrap\">\n            <div class=\"ols-ocr215-visual ols-ocr215-visual--rc\">\n              <div class=\"ols-ocr215-visual-panel\">\n                <div class=\"ols-ocr215-visual-kicker\">Redox or not?<\/div>\n                <div class=\"ols-ocr215-visual-main\">Redox<br>Classification<\/div>\n                <div class=\"ols-ocr215-config-line\" aria-hidden=\"true\"><span>metals, acids, unfamiliar equations<\/span><\/div>\n              <\/div>\n            <\/div>\n            <div class=\"ols-ocr215-card-num\">4<\/div>\n            <span class=\"ols-ocr215-card-status ols-ocr215-card-status--available\">Available<\/span>\n          <\/div>\n          <div class=\"ols-ocr215-card-body\">\n            <p class=\"ols-ocr215-card-title\">Redox Classification<\/p>\n            <p class=\"ols-ocr215-card-desc\">Classifying reactions with oxidation numbers: redox or not, s-block and p-block examples, metals with acids, and unfamiliar equations.<\/p>\n            <span class=\"ols-ocr215-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      <\/div>\n    <\/div>\n  <\/section>\n\n  <!-- SPECIFICATION -->\n  <section class=\"ols-ocr215-spec-section\">\n    <div class=\"ols-ocr215-container\">\n      <div class=\"ols-ocr215-spec-wrap\">\n        <div class=\"ols-ocr215-spec-pill\">Specification Coverage<\/div>\n        <h2 class=\"ols-ocr215-spec-heading\">2.1.5 Redox &#8211; OCR A Level Chemistry A<\/h2>\n        <p class=\"ols-ocr215-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-ocr215-spec-group-title\">2.1.5 Redox<\/h3>\n        <div class=\"ols-ocr215-spec-rows\">\n          <div class=\"ols-ocr215-spec-row ols-ocr215-spec-row--light\"><div class=\"ols-ocr215-spec-code\">2.1.5(a)<\/div><div class=\"ols-ocr215-spec-text\">rules for assigning and calculating oxidation number for atoms in elements, compounds and ions<\/div><\/div>\n          <div class=\"ols-ocr215-spec-row ols-ocr215-spec-row--mid\"><div class=\"ols-ocr215-spec-code ols-ocr215-spec-code--mid\">2.1.5(b)<\/div><div class=\"ols-ocr215-spec-text\">writing formulae using oxidation numbers<\/div><\/div>\n          <div class=\"ols-ocr215-spec-row ols-ocr215-spec-row--light\"><div class=\"ols-ocr215-spec-code\">2.1.5(c)<\/div><div class=\"ols-ocr215-spec-text\">use of a Roman numeral to indicate the magnitude of the oxidation number when an element may have compounds\/ions with different oxidation numbers<\/div><\/div>\n          <div class=\"ols-ocr215-spec-row ols-ocr215-spec-row--mid\"><div class=\"ols-ocr215-spec-code ols-ocr215-spec-code--mid\">2.1.5(d)<\/div><div class=\"ols-ocr215-spec-text\">oxidation and reduction in terms of:<div class=\"ols-ocr215-spec-sub-list\"><div class=\"ols-ocr215-spec-sub-row\"><div class=\"ols-ocr215-spec-sub-code\">i<\/div><div class=\"ols-ocr215-spec-sub-text\">electron transfer<\/div><\/div><div class=\"ols-ocr215-spec-sub-row\"><div class=\"ols-ocr215-spec-sub-code\">ii<\/div><div class=\"ols-ocr215-spec-sub-text\">changes in oxidation number<\/div><\/div><\/div><\/div><\/div>\n          <div class=\"ols-ocr215-spec-row ols-ocr215-spec-row--light\"><div class=\"ols-ocr215-spec-code\">2.1.5(e)<\/div><div class=\"ols-ocr215-spec-text\">redox reactions of metals with acids to form salts, including full equations<\/div><\/div>\n          <div class=\"ols-ocr215-spec-row ols-ocr215-spec-row--mid\"><div class=\"ols-ocr215-spec-code ols-ocr215-spec-code--mid\">2.1.5(f)<\/div><div class=\"ols-ocr215-spec-text\">interpretation of redox equations in (e) and of unfamiliar redox reactions to make predictions in terms of oxidation numbers and electron loss\/gain<\/div><\/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\": \"CollectionPage\",\n      \"@id\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-1-5-redox\/#webpage\",\n      \"url\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-1-5-redox\/\",\n      \"name\": \"2.1.5 Redox | OCR A A Level Chemistry | Online Learning System\",\n      \"description\": \"OCR A A Level Chemistry 2.1.5 Redox revision notes: oxidation numbers, electron transfer and half-equations, disproportionation, redox classification.\",\n      \"isPartOf\": {\n        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