{"id":4510,"date":"2026-05-28T05:25:16","date_gmt":"2026-05-28T04:25:16","guid":{"rendered":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/cp-7-analysis-of-inorganic-and-organic-unknowns\/"},"modified":"2026-06-10T10:57:34","modified_gmt":"2026-06-10T09:57:34","slug":"cp-7-analysis-of-inorganic-and-organic-unknowns","status":"publish","type":"page","link":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/core-practicals\/cp-7-analysis-of-inorganic-and-organic-unknowns\/","title":{"rendered":"CP 7 &#8211; Analysis of Inorganic and Organic Unknowns"},"content":{"rendered":"\n<aside class=\"ols-sidebar\">\r\n  <div class=\"ols-sidebar-header\">\r\n    <h3>Revision Notes<\/h3>\r\n    <p>Edexcel A Level Chemistry<\/p>\r\n  <\/div>\r\n\r\n  <div class=\"ols-topic-group\">\r\n    <h4>Core Practicals<\/h4>\r\n    <ul class=\"ols-topic-list\">\r\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/core-practicals\/cp-1-molar-volume-of-a-gas\/\">CP1: Molar Volume of a Gas<\/a><\/li>\r\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/core-practicals\/cp-2-prepare-a-standard-solution\/\">CP2: Prepare a Standard Solution<\/a><\/li>\r\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/core-practicals\/cp-3-concentration-of-hcl-by-titration\/\">CP3: Concentration of HCl by Titration<\/a><\/li>\r\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/core-practicals\/cp-4-hydrolysis-of-halogenoalkanes\/\">CP4: Hydrolysis of Halogenoalkanes<\/a><\/li>\r\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/core-practicals\/cp-5-oxidation-of-ethanol\/\">CP5: Oxidation of Ethanol<\/a><\/li>\r\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/core-practicals\/cp-6-chlorination-of-2-methylpropan-2-ol\/\">CP6: Chlorination of 2-methylpropan-2-ol<\/a><\/li>\r\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/core-practicals\/cp-7-analysis-of-inorganic-and-organic-unknowns\/\">CP7: Analysis of Inorganic and Organic Unknowns<\/a><\/li>\r\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/core-practicals\/cp-8-enthalpy-change-via-hess-law\/\">CP8: Enthalpy Change via Hess\u2019s Law<\/a><\/li>\r\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/core-practicals\/cp-9-electrochemical-cells\/\">CP9: Electrochemical Cells<\/a><\/li>\r\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/core-practicals\/cp-10-titration-of-edta\/\">CP10: Titration of EDTA<\/a><\/li>\r\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/core-practicals\/cp-11-rates-of-reaction-clock\/\">CP11: Rates of Reaction (Clock)<\/a><\/li>\r\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/core-practicals\/cp-12-continuous-monitoring-rates\/\">CP12: Continuous Monitoring Rates<\/a><\/li>\r\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/core-practicals\/cp-13-preparation-of-aspirin\/\">CP13: Preparation of Aspirin<\/a><\/li>\r\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/core-practicals\/cp-14-thin-layer-chromatography\/\">CP14: Thin Layer Chromatography<\/a><\/li>\r\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/core-practicals\/cp-15-preparing-organic-compound\/\">CP15: Preparing Organic Compound<\/a><\/li>\r\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/core-practicals\/cp-16-testing-organic-unknowns\/\">CP16: Testing Organic Unknowns<\/a><\/li>\r\n    <\/ul>\r\n  <\/div>\r\n\r\n  <div class=\"ols-topic-group\">\r\n    <h4>Useful Links<\/h4>\r\n    <ul class=\"ols-topic-list\">\r\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/\">Edexcel A Level Chemistry<\/a><\/li>\r\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/core-practicals\/\">Core Practicals<\/a><\/li>\r\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-5-formulae-equations-and-amounts-of-substance\/\">Formulae, Equations and Amounts of Substance<\/a><\/li>\r\n    <\/ul>\r\n  <\/div>\r\n<\/aside>\r\n\r\n<script>\r\n(function () {\r\n  var sidebar = document.querySelector('.ols-sidebar');\r\n  if (!sidebar) return;\r\n\r\n  var currentPath = window.location.pathname.replace(\/\\\/$\/, '');\r\n\r\n  sidebar.querySelectorAll('.ols-topic-list li').forEach(function (li) {\r\n    li.classList.remove('active');\r\n\r\n    var link = li.querySelector('a');\r\n    if (!link) return;\r\n\r\n    var linkPath = new URL(link.href).pathname.replace(\/\\\/$\/, '');\r\n\r\n    if (linkPath === currentPath) {\r\n      li.classList.add('active');\r\n    }\r\n  });\r\n})();\r\n<\/script>\n\n<section class=\"ols-cp7-page\" id=\"ols-cp7-page\">\n  <style>\n    .ols-cp7-page {\n      --navy:#1C244B;\n      --blue:#2563eb;\n      --light-blue:#eef4ff;\n     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padding:22px 18px; border-radius:22px; }\n      .ols-author-avatar-img { width:72px; height:72px; }\n      .ols-author-title { font-size:24px; }\n      .ols-author-description { font-size:15px; }\n      .ols-image-card, .ols-image-frame { border-radius:20px; }\n      .ols-image-frame { border-radius:20px 20px 0 0; }\n      .ols-lightbox { padding:12px; }\n      .ols-lightbox p { display:none; }\n    }\n  <\/style>\n\n  <div class=\"ols-cp7-layout\">\n\n    <main class=\"ols-cp7-main\">\n      <nav class=\"ols-cp7-breadcrumbs\" aria-label=\"Breadcrumb\">\n        <a href=\"\/xyz\/revision-notes\/\">Revision Notes<\/a> \/\n        <a href=\"\/xyz\/revision-notes\/a-level-chemistry\/\">A Level Chemistry<\/a> \/\n        <a href=\"\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/\">Edexcel<\/a> \/\n        <a href=\"\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/core-practicals\/\">Core Practicals<\/a> \/\n        <span>CP7: Analysis of Inorganic and Organic Unknowns<\/span>\n      <\/nav>\n\n      <header class=\"ols-title-card\">\n        <h1>CP7: Analysis of Inorganic and Organic Unknowns<\/h1>\n        <p class=\"ols-page-intro\">This practical is an evidence trail. Students test unknown organic liquids A, B and C, then inorganic solids X, Y and Z. The exam skill is to connect each observation to an inference, then use the full pattern of results to identify the unknown.<\/p>\n        <div class=\"ols-badges\">\n          <div class=\"ols-badge\">Exam board: Edexcel<\/div>\n          <div class=\"ols-badge\">Paper 3: General and Practical Principles in Chemistry<\/div>\n        <\/div>\n        <div class=\"ols-author\">\n          <img decoding=\"async\" class=\"ols-author-avatar-img\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/05\/Author-Profile.jpeg\" alt=\"Dr. Mohammed Al-Fatah\">\n          <div class=\"ols-author-content\">\n            <h2 class=\"ols-author-title\">Written by: Dr. Mohammed Al-Fatah<\/h2>\n            <p class=\"ols-author-description\">Chemistry specialist revision notes for A Level Chemistry.<\/p>\n            <a class=\"ols-linkedin-pill\" href=\"https:\/\/www.linkedin.com\/in\/doctormohammedfatah\/\" target=\"_blank\" rel=\"noopener noreferrer\">\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\"><\/path>\n              <\/svg>\n              View LinkedIn Profile\n            <\/a>\n          <\/div>\n        <\/div>\n      <\/header>\n\n      <section class=\"ols-full-image\" aria-label=\"CP7 complete summary infographic\">\n        <div class=\"ols-image-card\">\n          <div class=\"ols-image-frame\">\n            <img decoding=\"async\" class=\"ols-lightbox-img\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/06\/Core-practical-analysis-of-unknowns.webp\" alt=\"Core practical 8 analysis of organic and inorganic unknowns summary infographic\">\n          <\/div>\n          <div class=\"ols-image-caption\">\n            <h3>The CP7 evidence trail<\/h3>\n            <p>Unknown \u2192 test \u2192 observation \u2192 inference \u2192 identity. This is the logic students should use throughout the practical.<\/p>\n          <\/div>\n        <\/div>\n      <\/section>\n\n      <article class=\"ols-note-card soft\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">1<\/div>\n          <h2>How CP7 Works<\/h2>\n        <\/div>\n        <p>The objective is to identify several unknown colourless organic liquids and inorganic solids. The practical does not rely on one isolated result. It relies on the <strong>pattern<\/strong> of positive and negative tests.<\/p>\n        <div class=\"ols-evidence-strip\">\n          <div class=\"ols-evidence-step\"><span>?<\/span><strong>Unknown<\/strong><\/div>\n          <div class=\"ols-evidence-step\"><span>\ud83e\uddea<\/span><strong>Test<\/strong><\/div>\n          <div class=\"ols-evidence-step\"><span>\ud83d\udc41<\/span><strong>Observation<\/strong><\/div>\n          <div class=\"ols-evidence-step\"><span>\u2192<\/span><strong>Inference<\/strong><\/div>\n          <div class=\"ols-evidence-step\"><span>\u2713<\/span><strong>Identity<\/strong><\/div>\n        <\/div>\n        <div class=\"ols-key-box\">\n          <p><strong>Key idea:<\/strong> Negative tests are useful. They tell you what the unknown is not, which helps remove incorrect identities.<\/p>\n        <\/div>\n      <\/article>\n\n      <article class=\"ols-note-card blue\" id=\"organic-unknowns\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">2<\/div>\n          <h2>Organic Unknowns A, B and C<\/h2>\n        <\/div>\n        <p>The organic section uses four tests: bromine water, acidified potassium dichromate(VI), Fehling\u2019s solution, and hydrolysis followed by silver nitrate. In the sample data, each organic unknown is identified by the test it responds to.<\/p>\n\n        <div class=\"ols-table-wrap\">\n          <table class=\"ols-table\">\n            <thead>\n              <tr>\n                <th>Test<\/th>\n                <th>A<\/th>\n                <th>B<\/th>\n                <th>C<\/th>\n                <th>Inference<\/th>\n              <\/tr>\n            <\/thead>\n            <tbody>\n              <tr>\n                <td><strong>Bromine water<\/strong><\/td>\n                <td class=\"no\">No change<\/td>\n                <td class=\"yes\">Orange \u2192 colourless<\/td>\n                <td class=\"no\">No change<\/td>\n                <td>B contains a C=C double bond, so B is an alkene.<\/td>\n              <\/tr>\n              <tr>\n                <td><strong>Acidified potassium dichromate(VI)<\/strong><\/td>\n                <td class=\"yes\">Orange \u2192 green<\/td>\n                <td class=\"no\">No change<\/td>\n                <td class=\"no\">No change<\/td>\n                <td>A is oxidised, so A contains an oxidisable functional group.<\/td>\n              <\/tr>\n              <tr>\n                <td><strong>Fehling\u2019s solution<\/strong><\/td>\n                <td class=\"no\">No brick-red precipitate<\/td>\n                <td class=\"no\">No brick-red precipitate<\/td>\n                <td class=\"no\">No brick-red precipitate<\/td>\n                <td>No aldehyde is detected in the sample data.<\/td>\n              <\/tr>\n              <tr>\n                <td><strong>Hydrolysis, acidification, then AgNO<sub>3<\/sub><\/strong><\/td>\n                <td class=\"no\">No precipitate<\/td>\n                <td class=\"no\">No precipitate<\/td>\n                <td class=\"yes\">Cream precipitate<\/td>\n                <td>C contains bromine after hydrolysis, so C is a bromoalkane.<\/td>\n              <\/tr>\n            <\/tbody>\n          <\/table>\n        <\/div>\n\n        <div class=\"ols-key-box\">\n          <p><strong>Final organic identifications:<\/strong> A = oxidisable alcohol, B = alkene, C = bromoalkane.<\/p>\n        <\/div>\n\n        <div class=\"ols-image-grid\">\n          <div class=\"ols-image-card\">\n            <div class=\"ols-image-frame\"><img decoding=\"async\" class=\"ols-lightbox-img\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/06\/Bromine-water-test-in-laboratory-setting.webp\" alt=\"Bromine water test showing only B decolourising from orange to colourless\"><\/div>\n            <div class=\"ols-image-caption\"><h3>Bromine water<\/h3><p>Only B decolourises bromine water. This is evidence for an alkene.<\/p><\/div>\n          <\/div>\n          <div class=\"ols-image-card\">\n            <div class=\"ols-image-frame\"><img decoding=\"async\" class=\"ols-lightbox-img\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/06\/Acidified-dichromate-test-setup.webp\" alt=\"Acidified potassium dichromate test showing orange to green colour change for A\"><\/div>\n            <div class=\"ols-image-caption\"><h3>Acidified dichromate<\/h3><p>Only A changes from orange to green, showing oxidation.<\/p><\/div>\n          <\/div>\n          <div class=\"ols-image-card\">\n            <div class=\"ols-image-frame\"><img decoding=\"async\" class=\"ols-lightbox-img\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/06\/Fehlings-Solution-Test-in-action.webp\" alt=\"Fehling solution test showing no brick-red precipitate in the CP7 sample data\"><\/div>\n            <div class=\"ols-image-caption\"><h3>Fehling\u2019s solution<\/h3><p>No brick-red precipitate forms in the CP7 sample data, so an aldehyde is not detected.<\/p><\/div>\n          <\/div>\n          <div class=\"ols-image-card\">\n            <div class=\"ols-image-frame\"><img decoding=\"async\" class=\"ols-lightbox-img\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/06\/Silver-nitrate-test-after-hydrolysis.webp\" alt=\"Silver nitrate test after hydrolysis showing cream precipitate for bromoalkane C\"><\/div>\n            <div class=\"ols-image-caption\"><h3>Hydrolysis then silver nitrate<\/h3><p>C gives a cream precipitate after hydrolysis, acidification and silver nitrate, consistent with a bromoalkane.<\/p><\/div>\n          <\/div>\n        <\/div>\n      <\/article>\n\n      <article class=\"ols-note-card red\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">3<\/div>\n          <h2>Fehling\u2019s Test: Positive Control<\/h2>\n        <\/div>\n        <p>The CP7 sample data gives no Fehling\u2019s reaction. However, students still need to recognise what a positive result would look like. Aldehydes reduce Fehling\u2019s solution to a <strong>brick-red precipitate<\/strong> of copper(I) oxide. Ketones do not react under these conditions.<\/p>\n        <div class=\"ols-image-grid\">\n          <div class=\"ols-image-card\">\n            <div class=\"ols-image-frame\"><img decoding=\"async\" class=\"ols-lightbox-img\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/06\/Positive-Fehlings-test-in-lab-setting.webp\" alt=\"Positive Fehling test showing brick red precipitate as a reference result for aldehydes\"><\/div>\n            <div class=\"ols-image-caption\"><h3>Reference positive result<\/h3><p>This is a positive control image, not the CP7 sample result. A brick-red precipitate would indicate an aldehyde.<\/p><\/div>\n          <\/div>\n          <div class=\"ols-image-card\">\n            <div class=\"ols-image-frame\"><img decoding=\"async\" class=\"ols-lightbox-img\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/06\/Halide-ion-test-in-lab-setting.webp\" alt=\"Halide ion test comparison showing white, cream and pale yellow silver halide precipitates\"><\/div>\n            <div class=\"ols-image-caption\"><h3>Link to silver halides<\/h3><p>After hydrolysis, silver nitrate can detect released halide ions by precipitate colour.<\/p><\/div>\n          <\/div>\n        <\/div>\n      <\/article>\n\n      <article class=\"ols-note-card green\" id=\"inorganic-unknowns\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">4<\/div>\n          <h2>Inorganic Unknowns X, Y and Z<\/h2>\n        <\/div>\n        <p>The inorganic section uses flame tests to identify cations, then precipitation and displacement tests to identify anions. The full identity comes from combining cation and anion evidence.<\/p>\n\n        <div class=\"ols-table-wrap\">\n          <table class=\"ols-table\">\n            <thead>\n              <tr>\n                <th>Test<\/th>\n                <th>X<\/th>\n                <th>Y<\/th>\n                <th>Z<\/th>\n              <\/tr>\n            <\/thead>\n            <tbody>\n              <tr>\n                <td><strong>Flame test<\/strong><\/td>\n                <td>Red-orange, so Ca<sup>2+<\/sup><\/td>\n                <td>Yellow, so Na<sup>+<\/sup><\/td>\n                <td>Lilac, so K<sup>+<\/sup><\/td>\n              <\/tr>\n              <tr>\n                <td><strong>HNO<sub>3<\/sub>, AgNO<sub>3<\/sub>, then dilute NH<sub>3<\/sub><\/strong><\/td>\n                <td>Cream precipitate, not dissolved in dilute NH<sub>3<\/sub>, so Br<sup>&#8211;<\/sup><\/td>\n                <td>No change<\/td>\n                <td>Fizzing with acid, then no further silver halide evidence<\/td>\n              <\/tr>\n              <tr>\n                <td><strong>HNO<sub>3<\/sub>, then BaCl<sub>2<\/sub><\/strong><\/td>\n                <td>No change<\/td>\n                <td>White precipitate, so SO<sub>4<\/sub><sup>2-<\/sup><\/td>\n                <td>Fizzing with acid, then no lasting white precipitate<\/td>\n              <\/tr>\n              <tr>\n                <td><strong>Chlorine water<\/strong><\/td>\n                <td>Orange solution forms, so Br<sub>2<\/sub> is produced from Br<sup>&#8211;<\/sup><\/td>\n                <td>No change<\/td>\n                <td>Slight fizzing<\/td>\n              <\/tr>\n            <\/tbody>\n          <\/table>\n        <\/div>\n\n        <div class=\"ols-key-box\">\n          <p><strong>Final inorganic identifications:<\/strong> X = calcium bromide, CaBr<sub>2<\/sub>; Y = sodium sulfate, Na<sub>2<\/sub>SO<sub>4<\/sub>; Z = potassium carbonate, K<sub>2<\/sub>CO<sub>3<\/sub>.<\/p>\n        <\/div>\n\n        <div class=\"ols-image-grid\">\n          <div class=\"ols-image-card\">\n            <div class=\"ols-image-frame\"><img decoding=\"async\" class=\"ols-lightbox-img\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/06\/Flame-test-colours-and-cation-identification.webp\" alt=\"Flame test colours for required metal cations including lithium sodium potassium calcium strontium and barium\"><\/div>\n            <div class=\"ols-image-caption\"><h3>Flame tests<\/h3><p>Students should recognise the required cation colours, including Na<sup>+<\/sup> yellow, K<sup>+<\/sup> lilac and Ca<sup>2+<\/sup> brick red or red-orange.<\/p><\/div>\n          <\/div>\n          <div class=\"ols-image-card\">\n            <div class=\"ols-image-frame\"><img decoding=\"async\" class=\"ols-lightbox-img\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/06\/Halide-ion-test-in-lab-setting.webp\" alt=\"Silver nitrate halide test showing chloride bromide and iodide precipitates\"><\/div>\n            <div class=\"ols-image-caption\"><h3>Halide ion test<\/h3><p>Silver nitrate gives AgCl white, AgBr cream and AgI pale yellow. X gives the bromide result.<\/p><\/div>\n          <\/div>\n          <div class=\"ols-image-card\">\n            <div class=\"ols-image-frame\"><img decoding=\"async\" class=\"ols-lightbox-img\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/06\/Sulfate-ion-test-infographic-and-lab-setup.webp\" alt=\"Sulfate ion test showing white barium sulfate precipitate\"><\/div>\n            <div class=\"ols-image-caption\"><h3>Sulfate ion test<\/h3><p>Y gives a white precipitate with acidified barium chloride, showing sulfate ions.<\/p><\/div>\n          <\/div>\n          <div class=\"ols-image-card\">\n            <div class=\"ols-image-frame\"><img decoding=\"async\" class=\"ols-lightbox-img\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/06\/Carbonate-ion-test-demonstration.webp\" alt=\"Carbonate ion test showing fizzing with acid and cloudy limewater\"><\/div>\n            <div class=\"ols-image-caption\"><h3>Carbonate clue<\/h3><p>Z fizzes with acid, showing carbonate ions are present.<\/p><\/div>\n          <\/div>\n        <\/div>\n      <\/article>\n\n      <section class=\"ols-full-image\" aria-label=\"CP7 inorganic evidence guide\">\n        <div class=\"ols-image-card\">\n          <div class=\"ols-image-frame\">\n            <img decoding=\"async\" class=\"ols-lightbox-img\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/06\/CP8-Inorganic-Unknowns-Identification-Guide.webp\" alt=\"CP7 inorganic unknowns identification guide for calcium bromide sodium sulfate and potassium carbonate\">\n          <\/div>\n          <div class=\"ols-image-caption\">\n            <h3>Inorganic unknowns guide<\/h3>\n            <p>This visual summary links the flame test, halide test, sulfate test and chlorine water test to X, Y and Z.<\/p>\n          <\/div>\n        <\/div>\n      <\/section>\n\n      <article class=\"ols-note-card purple\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">5<\/div>\n          <h2>Chlorine Water Displacement<\/h2>\n        <\/div>\n        <p>Chlorine is more reactive than bromine and iodine, so chlorine can displace bromide and iodide ions from solution. In CP7, X forms an orange solution with chlorine water, showing that bromide ions have been oxidised to bromine.<\/p>\n        <div class=\"ols-image-grid\">\n          <div class=\"ols-image-card\">\n            <div class=\"ols-image-frame\"><img decoding=\"async\" class=\"ols-lightbox-img\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/06\/Chlorine-water-displacement-reactions.webp\" alt=\"Chlorine water displacement reactions showing chloride bromide and iodide results\"><\/div>\n            <div class=\"ols-image-caption\"><h3>Displacement comparison<\/h3><p>Chloride gives no visible displacement, bromide gives orange bromine, and iodide gives brown iodine.<\/p><\/div>\n          <\/div>\n          <div class=\"ols-image-card\">\n            <div class=\"ols-image-frame\"><img decoding=\"async\" class=\"ols-lightbox-img\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/06\/Silver-nitrate-test-after-hydrolysis.webp\" alt=\"Cream silver bromide precipitate after hydrolysis and silver nitrate addition\"><\/div>\n            <div class=\"ols-image-caption\"><h3>Consistent evidence for bromide<\/h3><p>The chlorine water result agrees with the cream AgBr precipitate from the silver nitrate test.<\/p><\/div>\n          <\/div>\n        <\/div>\n      <\/article>\n\n      <section class=\"ols-interactive\" id=\"interactive-evidence\">\n        <h2>Interactive Evidence Trail<\/h2>\n        <p>Click each button to reveal how the observations lead to the identity. This mirrors the thinking students need in the practical and in exam questions.<\/p>\n        <div class=\"ols-interactive-controls\">\n          <button type=\"button\" data-target=\"ols-a\">Identify A<\/button>\n          <button type=\"button\" data-target=\"ols-b\">Identify B<\/button>\n          <button type=\"button\" data-target=\"ols-c\">Identify C<\/button>\n          <button type=\"button\" data-target=\"ols-x\">Identify X<\/button>\n          <button type=\"button\" data-target=\"ols-y\">Identify Y<\/button>\n          <button type=\"button\" data-target=\"ols-z\">Identify Z<\/button>\n        <\/div>\n\n        <div id=\"ols-a\" class=\"ols-result-panel is-visible\">\n          <h3>A = oxidisable alcohol<\/h3>\n          <ul>\n            <li>Acidified dichromate changes orange to green.<\/li>\n            <li>Fehling\u2019s solution gives no brick-red precipitate.<\/li>\n            <li>The best functional-group inference is an oxidisable alcohol rather than an aldehyde.<\/li>\n          <\/ul>\n        <\/div>\n\n        <div id=\"ols-b\" class=\"ols-result-panel\">\n          <h3>B = alkene<\/h3>\n          <ul>\n            <li>Bromine water changes from orange to colourless.<\/li>\n            <li>This is an addition reaction across a C=C double bond.<\/li>\n            <li>The organic product is a 1,2-dibromo compound.<\/li>\n          <\/ul>\n        <\/div>\n\n        <div id=\"ols-c\" class=\"ols-result-panel\">\n          <h3>C = bromoalkane<\/h3>\n          <ul>\n            <li>C is warmed with ethanol and sodium hydroxide to hydrolyse the halogenoalkane.<\/li>\n            <li>The mixture is acidified with nitric acid before silver nitrate is added.<\/li>\n            <li>A cream precipitate shows AgBr, so C is a bromoalkane.<\/li>\n          <\/ul>\n        <\/div>\n\n        <div id=\"ols-x\" class=\"ols-result-panel\">\n          <h3>X = calcium bromide, CaBr<sub>2<\/sub><\/h3>\n          <ul>\n            <li>Red-orange flame indicates Ca<sup>2+<\/sup>.<\/li>\n            <li>Cream precipitate with AgNO<sub>3<\/sub> indicates Br<sup>&#8211;<\/sup>.<\/li>\n            <li>Orange solution with chlorine water confirms Br<sub>2<\/sub> is formed from Br<sup>&#8211;<\/sup>.<\/li>\n          <\/ul>\n        <\/div>\n\n        <div id=\"ols-y\" class=\"ols-result-panel\">\n          <h3>Y = sodium sulfate, Na<sub>2<\/sub>SO<sub>4<\/sub><\/h3>\n          <ul>\n            <li>Yellow flame indicates Na<sup>+<\/sup>.<\/li>\n            <li>White precipitate with acidified barium chloride indicates SO<sub>4<\/sub><sup>2-<\/sup>.<\/li>\n            <li>No halide or chlorine-water displacement evidence is observed.<\/li>\n          <\/ul>\n        <\/div>\n\n        <div id=\"ols-z\" class=\"ols-result-panel\">\n          <h3>Z = potassium carbonate, K<sub>2<\/sub>CO<sub>3<\/sub><\/h3>\n          <ul>\n            <li>Lilac flame indicates K<sup>+<\/sup>.<\/li>\n            <li>Fizzing with acid indicates CO<sub>3<\/sub><sup>2-<\/sup>.<\/li>\n            <li>The carbonate ion reacts with acid to produce carbon dioxide gas.<\/li>\n          <\/ul>\n        <\/div>\n      <\/section>\n\n      <article class=\"ols-note-card blue\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">6<\/div>\n          <h2>Ionic Equations and Reagent Roles<\/h2>\n        <\/div>\n        <p>These are the equations students should be able to write from the CP7 data. They also explain why acidification is important before precipitation tests.<\/p>\n\n        <div class=\"ols-equation-grid\">\n          <div class=\"ols-equation-card\">\n            <h3>Carbonate with acid<\/h3>\n            <div class=\"ols-equation\">CO<sub>3<\/sub><sup>2-<\/sup> + 2H<sup>+<\/sup> \u2192 CO<sub>2<\/sub> + H<sub>2<\/sub>O<\/div>\n          <\/div>\n          <div class=\"ols-equation-card\">\n            <h3>Silver bromide precipitate<\/h3>\n            <div class=\"ols-equation\">Ag<sup>+<\/sup> + Br<sup>&#8211;<\/sup> \u2192 AgBr<\/div>\n          <\/div>\n          <div class=\"ols-equation-card\">\n            <h3>Barium sulfate precipitate<\/h3>\n            <div class=\"ols-equation\">Ba<sup>2+<\/sup> + SO<sub>4<\/sub><sup>2-<\/sup> \u2192 BaSO<sub>4<\/sub><\/div>\n          <\/div>\n          <div class=\"ols-equation-card\">\n            <h3>Bromide displaced by chlorine<\/h3>\n            <div class=\"ols-equation\">2Br<sup>&#8211;<\/sup> + Cl<sub>2<\/sub> \u2192 Br<sub>2<\/sub> + 2Cl<sup>&#8211;<\/sup><\/div>\n          <\/div>\n        <\/div>\n\n        <div class=\"ols-warning-box\">\n          <p><strong>Exam trap:<\/strong> Nitric acid is added before silver nitrate to react with carbonate ions. This prevents silver carbonate forming and masking the halide result.<\/p>\n        <\/div>\n      <\/article>\n\n      <article class=\"ols-note-card soft\" id=\"exam-style\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">7<\/div>\n          <h2>Exam-Style Data Practice<\/h2>\n        <\/div>\n        <p>CP7 links directly to exam questions where students must identify unknowns from observations, spectra or calculation data.<\/p>\n\n        <h3>Unknown solution matrix<\/h3>\n        <p>Four unknown solutions are sodium carbonate, barium chloride, dilute hydrochloric acid and dilute sulfuric acid. From the pairwise observations, the identities are:<\/p>\n        <div class=\"ols-table-wrap\">\n          <table class=\"ols-table\">\n            <thead>\n              <tr><th>Letter<\/th><th>Identity<\/th><th>Reasoning clue<\/th><\/tr>\n            <\/thead>\n            <tbody>\n              <tr><td>A<\/td><td>Sulfuric acid<\/td><td>Forms a white precipitate with barium chloride and reacts with carbonate.<\/td><\/tr>\n              <tr><td>B<\/td><td>Hydrochloric acid<\/td><td>Reacts with carbonate but does not form a sulfate precipitate.<\/td><\/tr>\n              <tr><td>C<\/td><td>Barium chloride<\/td><td>Forms a white precipitate with sulfuric acid.<\/td><\/tr>\n              <tr><td>D<\/td><td>Sodium carbonate<\/td><td>Effervescence occurs with acids.<\/td><\/tr>\n            <\/tbody>\n          <\/table>\n        <\/div>\n\n        <h3>Spectroscopy and formula question<\/h3>\n        <p>The organic compound has percentage composition 38.7% carbon, 9.7% hydrogen and 52.6% oxygen. The answer pathway is:<\/p>\n        <ol>\n          <li>Empirical formula = CH<sub>2<\/sub>O.<\/li>\n          <li>Molecular ion peak at m\/z = 62, so M<sub>r<\/sub> = 62.<\/li>\n          <li>Molecular formula = C<sub>2<\/sub>H<sub>6<\/sub>O<sub>2<\/sub>.<\/li>\n          <li>Broad absorption at approximately 3400 cm<sup>-1<\/sup> shows O-H.<\/li>\n          <li>A fragment such as CHO<sup>+<\/sup> at m\/z 31 supports the structure.<\/li>\n          <li>The compound is CH<sub>2<\/sub>OHCH<sub>2<\/sub>OH, ethane-1,2-diol.<\/li>\n        <\/ol>\n      <\/article>\n\n      <article class=\"ols-note-card green\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">8<\/div>\n          <h2>What Students Usually Miss<\/h2>\n        <\/div>\n        <ul>\n          <li><strong>Do not ignore negative results.<\/strong> Fehling\u2019s solution has no reaction in the CP7 sample data, which helps rule out an aldehyde.<\/li>\n          <li><strong>Do not identify C directly from silver nitrate.<\/strong> The halogenoalkane must first be hydrolysed so halide ions are released.<\/li>\n          <li><strong>Do not forget acidification.<\/strong> Nitric acid removes carbonate interference before the silver nitrate test.<\/li>\n          <li><strong>Do not use flame colour alone for the full identity.<\/strong> The flame test gives the cation only. You still need the anion tests.<\/li>\n          <li><strong>Do not confuse AgBr and BaSO<sub>4<\/sub>.<\/strong> AgBr is cream and comes from silver nitrate with bromide. BaSO<sub>4<\/sub> is white and comes from barium chloride with sulfate.<\/li>\n        <\/ul>\n      <\/article>\n    <\/main>\n  <\/div>\n\n  <div class=\"ols-lightbox\" id=\"olsCp7Lightbox\" aria-hidden=\"true\">\n    <button type=\"button\" aria-label=\"Close image\">\u00d7<\/button>\n    <img decoding=\"async\" src=\"\" alt=\"\">\n    <p><\/p>\n  <\/div>\n\n  <script>\n    (function(){\n      var page = document.getElementById('ols-cp7-page');\n      if(!page) return;\n\n      var lb = page.querySelector('#olsCp7Lightbox');\n      var lbImg = lb.querySelector('img');\n      var lbText = lb.querySelector('p');\n      var closeBtn = lb.querySelector('button');\n\n      function openLightbox(img){\n        if(!img) return;\n        lbImg.src = img.currentSrc || img.src;\n        lbImg.alt = img.alt || '';\n        lbText.textContent = img.alt || 'Image preview';\n        lb.classList.add('is-open');\n        lb.setAttribute('aria-hidden','false');\n        document.documentElement.style.overflow = 'hidden';\n      }\n\n      function closeLightbox(){\n        lb.classList.remove('is-open');\n        lb.setAttribute('aria-hidden','true');\n        lbImg.src = '';\n        lbImg.alt = '';\n        lbText.textContent = '';\n        document.documentElement.style.overflow = '';\n      }\n\n      page.addEventListener('click', function(e){\n        var frame = e.target.closest('.ols-image-frame');\n        if(!frame || !page.contains(frame)) return;\n        var img = frame.querySelector('img');\n        openLightbox(img);\n      });\n\n      closeBtn.addEventListener('click', closeLightbox);\n      lb.addEventListener('click', function(e){\n        if(e.target === lb) closeLightbox();\n      });\n      document.addEventListener('keydown', function(e){\n        if(e.key === 'Escape') closeLightbox();\n      });\n\n      var interactive = page.querySelector('.ols-interactive');\n      if(interactive){\n        var buttons = interactive.querySelectorAll('button[data-target]');\n        var panels = interactive.querySelectorAll('.ols-result-panel');\n        buttons.forEach(function(btn){\n          btn.addEventListener('click', function(){\n            buttons.forEach(function(b){ b.classList.remove('is-active'); });\n            panels.forEach(function(p){ p.classList.remove('is-visible'); });\n            btn.classList.add('is-active');\n            var target = interactive.querySelector('#' + btn.getAttribute('data-target'));\n            if(target) target.classList.add('is-visible');\n          });\n        });\n      }\n    })();\n  <\/script>\n\n  <script type=\"application\/ld+json\">\n  {\n    \"@context\":\"https:\/\/schema.org\",\n    \"@type\":\"LearningResource\",\n    \"name\":\"CP7: Analysis of Inorganic and Organic Unknowns\",\n    \"description\":\"A Level Chemistry revision notes for Edexcel CP7, covering inorganic and organic unknown analysis, flame tests, bromine water, acidified dichromate, Fehling's solution, silver nitrate, barium chloride and chlorine water displacement.\",\n    \"learningResourceType\":\"Revision notes\",\n    \"educationalLevel\":\"A Level\",\n    \"inLanguage\":\"en-GB\",\n    \"provider\":{\n      \"@type\":\"Organization\",\n      \"name\":\"Online Learning System\",\n      \"url\":\"https:\/\/www.onlinelearningsystem.net\/\"\n    },\n    \"about\":[\n      \"CP7\",\n      \"Qualitative analysis\",\n      \"Organic unknowns\",\n      \"Inorganic unknowns\",\n      \"Flame tests\",\n      \"Halide test\",\n      \"Sulfate test\",\n      \"Carbonate test\",\n      \"Bromine water\",\n      \"Acidified dichromate\"\n    ]\n  }\n  <\/script>\n<\/section>\n","protected":false},"excerpt":{"rendered":"<p>Revision Notes \/ A Level Chemistry \/ Edexcel \/ Core Practicals \/ CP7: Analysis of Inorganic and Organic Unknowns CP7: Analysis of Inorganic and Organic Unknowns This practical is an evidence trail. Students test unknown organic liquids A, B and C, then inorganic solids X, Y and Z. The exam skill is to connect each [&hellip;]<\/p>\n","protected":false},"author":12,"featured_media":0,"parent":4999,"menu_order":6,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-4510","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/pages\/4510","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=4510"}],"version-history":[{"count":0,"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/pages\/4510\/revisions"}],"up":[{"embeddable":true,"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/pages\/4999"}],"wp:attachment":[{"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/media?parent=4510"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}