{"id":3436,"date":"2026-05-13T07:35:50","date_gmt":"2026-05-13T06:35:50","guid":{"rendered":"https:\/\/www.onlinelearningsystem.net\/xyz\/?page_id=3436"},"modified":"2026-10-19T20:31:32","modified_gmt":"2026-10-19T19:31:32","slug":"bromine-water","status":"publish","type":"page","link":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-5-alkenes\/reactions-of-alkenes\/bromine-water\/","title":{"rendered":"Bromine Water"},"content":{"rendered":"\n<section class=\"ols-revision-page ols-alkene-bromine-water-page\">\n  <style>\n    .ols-revision-page {\n      --navy: #1C244B;\n      --blue: #2563eb;\n      --soft-blue: #eef4ff;\n      --soft-red: #fff7f7;\n      --soft-purple: #f7f0ff;\n      --soft-green: #f0f7f1;\n      --green: #3f8f46;\n      --red: #d94b2b;\n      --gold: #c9973a;\n      --grey-text: #667085;\n      --body-text: #1f2937;\n      --border: rgba(28, 36, 75, 0.14);\n      --shadow: 0 18px 45px rgba(28, 36, 75, 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0 8px;\n      font-size: 20px;\n      line-height: 1.3;\n      color: var(--navy);\n    }\n.ols-faq-item p {\n      margin: 0;\n      font-size: 16px;\n      line-height: 1.65;\n      color: var(--body-text);\n    }\n.ols-faq-card,\n      .ols-quicksnap-card,\n      .ols-attribution-card {\n        padding: 24px 18px;\n        border-radius: 22px;\n      }\n<\/style>\n\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 5 Alkenes<\/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-5-alkenes\/alkene-bonding\/\">Alkene Bonding<\/a>\r\n      <\/li>\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-5-alkenes\/geometric-isomerism\/\">Geometric Isomerism<\/a>\r\n      <\/li>\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-5-alkenes\/electrophilic-addition-mechanism\/\">Electrophilic Addition Mechanism<\/a>\r\n      <\/li>\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-5-alkenes\/reactions-of-alkenes\/\">Reactions of Alkenes<\/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-5-alkenes\/reactions-of-alkenes\/halogens\/\">Halogens<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-5-alkenes\/reactions-of-alkenes\/hydrogen-halide\/\">Hydrogen Halide<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-5-alkenes\/reactions-of-alkenes\/bromine-water\/\">Bromine Water<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-5-alkenes\/reactions-of-alkenes\/hydrogen\/\">Hydrogen<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-5-alkenes\/reactions-of-alkenes\/steam\/\">Steam<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-5-alkenes\/reactions-of-alkenes\/kmno4\/\">KMnO4<\/a>\r\n          <\/li>\r\n        <\/ul>\r\n      <\/li>\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-5-alkenes\/polymerisation-reactions\/\">Polymerisation Reactions<\/a>\r\n      <\/li>\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-5-alkenes\/polymer-waste\/\">Polymer Waste<\/a>\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-6-energetics\/\">Energetics<\/a>\r\n      <\/li>\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-7-intermolecular-forces\/\">Intermolecular Forces<\/a>\r\n      <\/li>\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-8A-redox-chemistry\/\">Redox Chemistry<\/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(\/\\\/+$\/, '')\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    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href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-5-alkenes\/\">Topic 5 Alkenes<\/a> \/\n        <span>Reactions of Alkenes: Bromine Water<\/span>\n      <\/nav>\n\n      <header class=\"ols-title-card\">\n        <h1>Reactions of Alkenes with Bromine Water<\/h1>\n        <p class=\"ols-page-intro\">A concise revision guide to the reaction of alkenes with bromine water, including the orange to colourless observation, why the reaction is a test for the alkene functional group and how the C=C double bond reacts by addition.<\/p>\n\n        <div class=\"ols-badges\">\n          <div class=\"ols-badge\">Exam board: Edexcel International<\/div>\n          <div class=\"ols-badge\">Topic 5: Alkenes<\/div>\n          <div class=\"ols-badge\">Reaction 3: Bromine Water<\/div>\n        <\/div>\n      <\/header>\n\n      <article class=\"ols-note-card\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">1<\/div>\n<h2>Before You Start<\/h2>\n<\/div>\n<p>This page builds on the GCSE bromine water test for alkenes.<\/p>\n<ul class=\"ols-list\">\n<li>Bromine water is orange. Alkenes decolourise it; alkanes do not.<\/li>\n<li><strong>Saturated<\/strong> hydrocarbons contain only C-C single bonds; <strong>unsaturated<\/strong> hydrocarbons contain at least one C=C double bond.<\/li>\n<li>Alkenes have the general formula C<sub>n<\/sub>H<sub>2n<\/sub>.<\/li>\n<li>In an <strong>addition reaction<\/strong>, atoms add across the C=C bond to form one product.<\/li>\n<\/ul>\n<\/article>\n<section class=\"ols-h5p-card ols-h5p-inline ols-h5p-recap\">\n<span class=\"ols-h5p-kicker\">Before you start<\/span>\n<h2>GCSE Recap: Saturated or Unsaturated?<\/h2>\n<p>Four quick GCSE questions on alkenes, alkanes and cracking before you look at the test in detail.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-content\" data-content-id=\"1271\"><\/div><\/div>\n<\/section>\n\n      <article class=\"ols-note-card soft\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">2<\/div>\n          <h2>The Overall Reaction<\/h2>\n        <\/div>\n\n        <p>Alkenes react with <strong>bromine water<\/strong> in an <strong>addition reaction<\/strong>. Bromine water is bromine dissolved in water, and the reaction takes place at <strong>room temperature<\/strong>.<\/p>\n        <p>The C=C double bond opens and atoms add across the double bond. This means the alkene becomes a saturated organic product.<\/p>\n        <p>The key observation is that the <strong>orange colour of bromine water decolourises to colourless<\/strong>.<\/p>\n\n        <div class=\"ols-reaction-summary\">\n          <div class=\"ols-summary-item\"><span>Reagent<\/span><strong>Bromine dissolved in water<\/strong><\/div>\n          <div class=\"ols-summary-item\"><span>Conditions<\/span><strong>Room temperature<\/strong><\/div>\n          <div class=\"ols-summary-item\"><span>Type of reaction<\/span><strong>Addition<\/strong><\/div>\n          <div class=\"ols-summary-item\"><span>Observation<\/span><strong>Orange \u2192 colourless<\/strong><\/div>\n        <\/div>\n\n        <div class=\"ols-key-box\">\n          <p><strong>Key idea:<\/strong> The colour change happens because bromine reacts with the C=C double bond, so bromine water is used as a chemical test for alkenes.<\/p>\n        <\/div>\n\n        <div class=\"ols-figure-card\">\n          <div class=\"ols-figure-image\">\n            <img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/10\/t5-cd-06-brwaterequation.svg\" alt=\"Ethene adding HOBr from bromine water to give 2-bromoethanol, displayed formulae\" width=\"1502\" height=\"1293\">\n          <\/div>\n          <div class=\"ols-figure-caption\">\n            <p>The C=C double bond reacts with bromine water, causing the orange colour to disappear.<\/p>\n          <\/div>\n        <\/div>\n      <\/article>\n<section class=\"ols-h5p-card ols-h5p-inline\">\n<span class=\"ols-h5p-kicker\">Check your understanding<\/span>\n<h2>Quick Check: Drop by Drop<\/h2>\n<p>Decide what it means when the orange colour stops disappearing.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-35\" class=\"h5p-iframe\" data-content-id=\"35\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Bromine Water MCQ: Adding the Reagent Drop by Drop\"><\/iframe><\/div><\/div>\n<\/section>\n\n      <article class=\"ols-note-card\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">3<\/div>\n          <h2>Using Bromine Water to Test for Alkenes<\/h2>\n        <\/div>\n\n        <p>Bromine water is commonly used to test whether an organic compound contains an <strong>alkene functional group<\/strong>.<\/p>\n        <p>If a C=C double bond is present, bromine water changes from <strong>orange to colourless<\/strong>. This positive test shows that the bromine has reacted with the alkene.<\/p>\n        <p>If there is no C=C double bond under these conditions, the orange colour is expected to remain.<\/p>\n\n        <div class=\"ols-test-grid\">\n          <div class=\"ols-test-card\">\n            <h3>Positive test<\/h3>\n            <p>Bromine water decolourises from orange to colourless. This suggests the compound contains a C=C double bond.<\/p>\n          <\/div>\n\n          <div class=\"ols-test-card\">\n            <h3>Negative test<\/h3>\n            <p>The orange colour remains. This suggests there is no alkene functional group reacting under the test conditions.<\/p>\n          <\/div>\n        <\/div>\n\n        <div class=\"ols-key-box\">\n          <p><strong>Exam focus:<\/strong> State both the reagent and the observation: bromine water changes from orange to colourless.<\/p>\n        <\/div>\n      <div class=\"ols-figure-card ols-zoom-pop\">\n<div class=\"ols-figure-image\">\n<a class=\"ols-image-fullscreen-link\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/10\/t5-img-26-brwatertest.jpg\" target=\"_blank\" rel=\"noopener\" aria-label=\"Open image fullscreen\">\n<img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/10\/t5-img-26-brwatertest.jpg\" alt=\"Two test tubes: bromine water shaken with an alkene turns from orange to colourless, with an alkane it stays orange\" data-fullscreen-src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/10\/t5-img-26-brwatertest.jpg\">\n<\/a>\n<\/div>\n<div class=\"ols-figure-caption\"><p>Shaken with an alkene, bromine water is decolourised from orange to colourless; with an alkane the orange colour remains.<\/p><\/div>\n<\/div>\n<\/article>\n<section class=\"ols-h5p-card ols-h5p-inline\">\n<span class=\"ols-h5p-kicker\">Check your understanding<\/span>\n<h2>Quick Check: Which Ones React?<\/h2>\n<p>Click every substance in the list that turns bromine water from orange to colourless.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-37\" class=\"h5p-iframe\" data-content-id=\"37\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Bromine Water Mark the Words: Which Substances Decolourise It\"><\/iframe><\/div><\/div>\n<\/section>\n\n      <article class=\"ols-note-card purple\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">4<\/div>\n          <h2>Why This Is an Addition Reaction<\/h2>\n        <\/div>\n\n        <p>Alkenes are unsaturated because they contain a <strong>carbon-carbon double bond, C=C<\/strong>. The double bond contains an electron-rich \u03c0 bond, which is the reactive part of the molecule.<\/p>\n        <p>During addition, the \u03c0 bond is broken and new bonds form to the two carbon atoms from the original double bond.<\/p>\n        <p>The overall result is that the molecule becomes more saturated because atoms have been added across the C=C bond.<\/p>\n\n        <div class=\"ols-definition-box\">\n          <div class=\"ols-definition-circle\">C=C<\/div>\n          <p><strong>Addition reaction:<\/strong> A reaction in which atoms are added across a double bond, converting an unsaturated molecule into a more saturated product.<\/p>\n        <\/div>\n\n        <div class=\"ols-key-box\">\n          <p><strong>Remember:<\/strong> In alkene addition reactions, the C=C double bond is the reactive site. The \u03c0 bond reacts first because it is electron-rich and more exposed than the \u03c3 bond.<\/p>\n        <\/div>\n      <\/article>\n<section class=\"ols-h5p-card ols-h5p-inline\">\n<span class=\"ols-h5p-kicker\">Check your understanding<\/span>\n<h2>Quick Check: Pick the Accurate Statement<\/h2>\n<p>In each round, choose the one statement that is accurate.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-36\" class=\"h5p-iframe\" data-content-id=\"36\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Bromine Water Summary: Addition, Saturation and a Negative Result\"><\/iframe><\/div><\/div>\n<\/section>\n\n      <article class=\"ols-note-card\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">5<\/div>\n          <h2>The Reaction Mechanism<\/h2>\n        <\/div>\n\n        <p>The reaction of an alkene with bromine water is linked to the same core idea as other alkene addition reactions: the electron-rich \u03c0 bond reacts first.<\/p>\n        <p>The C=C double bond provides electron density, allowing the reaction to begin. The double bond then opens and new bonds form across the two carbon atoms.<\/p>\n        <p>This explains why the characteristic orange colour disappears. Bromine is consumed as it reacts with the alkene.<\/p>\n\n        <div class=\"ols-mechanism-steps\">\n          <div class=\"ols-step-card\">\n            <h3>Step 1: The \u03c0 bond attacks Br\u03b4<sup>+<\/sup><\/h3>\n            <p>As Br<sub>2<\/sub> approaches, the \u03c0 bond induces a dipole in it. The \u03c0 electrons form a bond to Br\u03b4<sup>+<\/sup>, the Br-Br bond breaks heterolytically, and a carbocation and Br<sup>&#8211;<\/sup> form.<\/p>\n          <\/div>\n\n          <div class=\"ols-step-card\">\n            <h3>Step 2: Water attacks the carbocation<\/h3>\n            <p>Water is in large excess, so a lone pair on the oxygen atom of H<sub>2<\/sub>O usually bonds to the carbocation before Br<sup>&#8211;<\/sup> can. Some Br<sup>&#8211;<\/sup> does attack, so a little 1,2-dibromoethane also forms.<\/p>\n          <\/div>\n\n          <div class=\"ols-step-card\">\n            <h3>Step 3: H<sup>+<\/sup> is lost<\/h3>\n            <p>The oxygen now carries a positive charge. An O-H bond breaks and H<sup>+<\/sup> is lost, giving 2-bromoethanol from ethene. Bromine has been used up, so the orange colour disappears.<\/p>\n          <\/div>\n        <\/div>\n\n        \n      <\/article>\n<section class=\"ols-h5p-card ols-h5p-inline\">\n<span class=\"ols-h5p-kicker\">Check your understanding<\/span>\n<h2>Quick Check: How Far Does the Result Go?<\/h2>\n<p>Write a short explanation, then compare it with the mark points and the model answer.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-34\" class=\"h5p-iframe\" data-content-id=\"34\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Bromine Water Explain: What a Positive Result Does Not Prove\"><\/iframe><\/div><\/div>\n<\/section>\n\n      <article class=\"ols-note-card soft\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">6<\/div>\n          <h2>Common Exam Mistakes<\/h2>\n        <\/div>\n\n        <p>Students often lose marks by saying only that bromine water \u201cgoes clear\u201d without giving the full starting colour. The full observation is <strong>orange to colourless<\/strong>.<\/p>\n        <p>Another common error is to describe the reaction as substitution. This is incorrect for alkenes. The reaction is <strong>addition<\/strong> because atoms are added across the C=C double bond.<\/p>\n        <p>For a test question, the safest answer should include the reagent, condition and observation.<\/p>\n\n        <div class=\"ols-reaction-summary\">\n          <div class=\"ols-summary-item\"><span>Do say<\/span><strong>Bromine water decolourises from orange to colourless.<\/strong><\/div>\n          <div class=\"ols-summary-item\"><span>Do not just say<\/span><strong>It goes clear.<\/strong><\/div>\n          <div class=\"ols-summary-item\"><span>Reaction type<\/span><strong>Addition, not substitution.<\/strong><\/div>\n          <div class=\"ols-summary-item\"><span>Reason<\/span><strong>The C=C double bond opens.<\/strong><\/div>\n        <\/div>\n\n        <div class=\"ols-key-box\">\n          <p><strong>Exam focus:<\/strong> Link the observation to the alkene functional group. The colour change is evidence that a C=C double bond has reacted.<\/p>\n        <\/div>\n      <div class=\"ols-figure-card ols-zoom-pop\">\n<div class=\"ols-figure-image\">\n<a class=\"ols-image-fullscreen-link\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/10\/t5-img-27-brwaterlimits.jpg\" target=\"_blank\" rel=\"noopener\" aria-label=\"Open image fullscreen\">\n<img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/10\/t5-img-27-brwaterlimits.jpg\" alt=\"What a positive bromine water test shows and cannot show, with three wrong-versus-right exam statements\" data-fullscreen-src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/10\/t5-img-27-brwaterlimits.jpg\">\n<\/a>\n<\/div>\n<div class=\"ols-figure-caption\"><p>A positive bromine water test shows that a C=C bond is present, but not how many there are or where they are.<\/p><\/div>\n<\/div>\n<\/article>\n<section class=\"ols-h5p-card ols-h5p-inline\">\n<span class=\"ols-h5p-kicker\">Check your understanding<\/span>\n<h2>Quick Check: Bromine Water from Start to Finish<\/h2>\n<p>Each round covers one part of the page, from the observation to the mechanism. Choose the one accurate statement.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-1272\" class=\"h5p-iframe\" data-content-id=\"1272\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Bromine Water Summary: But-2-ene from Observation to Mechanism\"><\/iframe><\/div><\/div>\n<\/section>\n\n      \n\n      <section class=\"ols-faq-card\">\n<h2>FAQs<\/h2>\n<p>These questions secure the observation, product and limits of the bromine water test.<\/p>\n<div class=\"ols-faq-list\">\n<div class=\"ols-faq-item\">\n<h3>Is the product with bromine water 1,2-dibromoethane?<\/h3>\n<p>Mainly not. Water is in large excess, so it attacks the carbocation more often than Br<sup>&#8211;<\/sup> does. The main product from ethene is 2-bromoethanol, with some 1,2-dibromoethane. For the test itself, the observation earns the mark.<\/p>\n<\/div>\n<div class=\"ols-faq-item\">\n<h3>Why must I write &#8220;colourless&#8221; and not &#8220;goes clear&#8221;?<\/h3>\n<p>Clear means transparent, and orange bromine water is already clear. Colourless is the correct word. Write the full change: orange to colourless.<\/p>\n<\/div>\n<div class=\"ols-faq-item\">\n<h3>Can bromine water tell me which alkene I have?<\/h3>\n<p>No. Every compound with a C=C bond decolourises bromine water, so the test only shows that a C=C bond is present. It cannot tell ethene from propene or show how many double bonds a molecule has.<\/p>\n<\/div>\n<div class=\"ols-faq-item\">\n<h3>Why does an alkane not decolourise bromine water?<\/h3>\n<p>An alkane has only \u03c3 bonds and no \u03c0 electrons to attack bromine. At room temperature in the dark no reaction happens, so the orange colour stays. In UV light, alkanes react slowly by radical substitution instead.<\/p>\n<\/div>\n<div class=\"ols-faq-item\">\n<h3>Do I need to heat the sample with bromine water?<\/h3>\n<p>No. Shake the sample with a few drops of bromine water at room temperature. An alkene decolourises it straight away, so heating is not needed.<\/p>\n<\/div>\n<\/div>\n<\/section>\n\n      <!-- author card (moved to the end, 10 Oct 2026) -->\n      <div class=\"ols-author\">\n\n    <img decoding=\"async\"\n      class=\"ols-author-avatar-img\"\n      src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/05\/Author-Profile.jpeg\"\n      alt=\"Dr. Mohammed Al-Fatah\"\n    >\n\n    <div class=\"ols-author-content\">\n\n      <h2 class=\"ols-author-title\">\n        Written by: Dr. Mohammed Al-Fatah\n      <\/h2>\n\n      <p class=\"ols-author-description\">\n        Chemistry specialist revision notes for A Level Chemistry.\n      <\/p>\n\n      <a\n        class=\"ols-linkedin-pill\"\n        href=\"https:\/\/www.linkedin.com\/in\/doctormohammedfatah\/\"\n        target=\"_blank\"\n        rel=\"noopener noreferrer\"\n      >\n        <svg class=\"ols-linkedin-icon\" viewBox=\"0 0 24 24\" fill=\"currentColor\" aria-hidden=\"true\">\n          <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\"\/>\n        <\/svg>\n        View LinkedIn Profile\n      <\/a>\n\n    <\/div>\n\n  <\/div>\n\n\n      <section class=\"ols-related-card\">\n        <h2>Related Alkene Revision Notes<\/h2>\n        <p>Continue through Topic 5 by linking bromine water to halogen addition, hydrogen halide addition and the general electrophilic addition mechanism.<\/p>\n\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-5-alkenes\/electrophilic-addition-mechanism\/\">Electrophilic Addition Mechanism<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/\">Halogens<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/\">Hydrogen Halide<\/a>\n        <\/div>\n      <\/section>\n\n      <section class=\"ols-attribution-card ols-attr-std\" aria-label=\"Copyright notice\">\n<style id=\"ols-attribution-card-css\">.ols-attribution-card.ols-attr-std{background:linear-gradient(135deg,#ffffff,#f8fbff);border:1px solid rgba(28,36,75,0.14);border-radius:28px;box-shadow:0 18px 45px rgba(28,36,75,0.10);padding:34px;margin:24px 0;overflow:hidden;font-family:Poppins,Arial,sans-serif;box-sizing:border-box}.ols-attribution-card.ols-attr-std *{box-sizing:border-box}.ols-attribution-card.ols-attr-std p{margin:0;font-size:14px;line-height:1.65;font-weight:300;color:#667085}.ols-attribution-card.ols-attr-std strong{font-weight:700;color:#1C244B}@media (max-width:760px){.ols-attribution-card.ols-attr-std{padding:24px 18px;border-radius:22px}}<\/style>\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    <\/main>\n  \n\n<script type=\"application\/ld+json\">\n{\n    \"@context\": \"https:\/\/schema.org\",\n    \"@graph\": [\n        {\n            \"@type\": \"Organization\",\n            \"@id\": \"https:\/\/www.onlinelearningsystem.net\/#organization\",\n            \"name\": \"Online Learning System\",\n            \"url\": \"https:\/\/www.onlinelearningsystem.net\/\",\n            \"logo\": {\n                \"@type\": \"ImageObject\",\n                \"url\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2025\/07\/a-level-chemistry-virtual-lesson-tutor.webp\"\n            }\n        },\n        {\n            \"@type\": \"WebSite\",\n            \"@id\": \"https:\/\/www.onlinelearningsystem.net\/#website\",\n            \"url\": \"https:\/\/www.onlinelearningsystem.net\/\",\n            \"name\": \"Online Learning System\",\n            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An alkene decolourises it straight away, so heating is not needed.\"\n                    }\n                }\n            ]\n        }\n    ]\n}\n<\/script>\n\n<\/section>\n\n\n\n<p class=\"wp-block-paragraph\"><\/p>\n","protected":false},"excerpt":{"rendered":"<p>Revision Notes \/ A Level Chemistry \/ Edexcel International \/ Topic 5 Alkenes \/ Reactions of Alkenes: Bromine Water Reactions of Alkenes with Bromine Water A concise revision guide to the reaction of alkenes with bromine water, including the orange to colourless observation, why the reaction is a test for the alkene functional group and [&hellip;]<\/p>\n","protected":false},"author":12,"featured_media":0,"parent":4332,"menu_order":2,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-3436","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/pages\/3436","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=3436"}],"version-history":[{"count":0,"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/pages\/3436\/revisions"}],"up":[{"embeddable":true,"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/pages\/4332"}],"wp:attachment":[{"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/media?parent=3436"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}