{"id":11276,"date":"2026-09-27T14:51:34","date_gmt":"2026-09-27T13:51:34","guid":{"rendered":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/required-practicals\/rates-of-hydrolysis-of-halogenoalkanes\/"},"modified":"2026-10-03T08:38:11","modified_gmt":"2026-10-03T07:38:11","slug":"rates-of-hydrolysis-of-halogenoalkanes","status":"publish","type":"page","link":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/required-practicals\/rates-of-hydrolysis-of-halogenoalkanes\/","title":{"rendered":"Comparing the Rates of Hydrolysis of Halogenoalkanes"},"content":{"rendered":"<script src=\"https:\/\/cdnjs.cloudflare.com\/ajax\/libs\/three.js\/r128\/three.min.js\"><\/script>\n\n<section class=\"ols-revision-page ols-core-practical-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      --soft-orange: #fff7ed;\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, 0.10);\n      --inner-shadow: 0 10px 26px rgba(28, 36, 75, 0.08);\n      font-family: Poppins, Arial, sans-serif;\n      color: var(--navy);\n      background: #ffffff;\n    }\n\n    .ols-revision-page * { box-sizing: border-box; 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}\n    .ols-author-content { min-width: 0; }\n    .ols-author-title { margin: 0 0 4px; font-size: clamp(24px,3vw,34px); line-height: 1.15; font-weight: 700; color: var(--navy); letter-spacing: -0.03em; }\n    .ols-author-description { margin: 0; font-size: 17px; line-height: 1.7; font-weight: 300; color: var(--grey-text); }\n    .ols-linkedin-pill { display: inline-flex; align-items: center; justify-content: center; gap: 10px; margin-top: 16px; padding: 11px 18px; border-radius: 999px; background: linear-gradient(135deg,#0A66C2,#004182); color: #ffffff; text-decoration: none; font-size: 14px; line-height: 1; font-weight: 700; letter-spacing: 0.01em; box-shadow: 0 10px 22px rgba(10,102,194,0.24); position: relative; overflow: hidden; transition: transform 0.22s ease, box-shadow 0.22s ease; }\n    .ols-linkedin-pill::before { content: \"\"; position: absolute; top: 0; left: -120%; width: 100%; height: 100%; background: linear-gradient(120deg, rgba(255,255,255,0) 0%, rgba(255,255,255,0.28) 50%, rgba(255,255,255,0) 100%); transition: left 0.7s ease; }\n    .ols-linkedin-pill:hover { transform: translateY(-3px) scale(1.03); box-shadow: 0 16px 34px rgba(10,102,194,0.34), 0 0 0 6px rgba(10,102,194,0.10); color: #ffffff; }\n    .ols-linkedin-pill:hover::before { left: 120%; }\n    .ols-linkedin-icon { width: 18px; height: 18px; display: block; flex-shrink: 0; }\n\n    .ols-note-card.soft { background: linear-gradient(135deg, #ffffff 0%, var(--soft-red) 100%); }\n    .ols-note-card.purple { background: linear-gradient(135deg, #ffffff 0%, var(--soft-purple) 100%); }\n    .ols-note-card.orange { background: linear-gradient(135deg, #ffffff 0%, var(--soft-orange) 100%); }\n    .ols-note-title { display: flex; align-items: center; gap: 14px; margin-bottom: 20px; }\n    .ols-note-icon { width: 52px; height: 52px; border-radius: 16px; background: var(--navy); color: #ffffff; display: grid; place-items: center; font-size: 24px; font-weight: 800; flex-shrink: 0; }\n    .ols-note-title h2, .ols-h5p-card h2, .ols-related-card h2, .ols-faq-card h2 { margin: 0; font-size: clamp(28px, 3.5vw, 42px); line-height: 1.15; font-weight: 800; color: #111827; letter-spacing: -0.03em; }\n    .ols-h5p-card h2, .ols-related-card h2, .ols-faq-card h2 { margin-bottom: 14px; }\n    .ols-note-card p, .ols-note-card li { font-size: clamp(15px, 1.25vw, 17px); line-height: 1.65; font-weight: 300; color: var(--body-text); }\n    .ols-h5p-card p, .ols-related-card p, .ols-faq-card p { font-size: clamp(15px, 1.3vw, 18px); line-height: 1.65; font-weight: 300; color: var(--body-text); }\n    .ols-note-card strong, .ols-h5p-card strong, .ols-related-card strong, .ols-faq-card strong { font-weight: 700; color: var(--navy); }\n    .ols-note-card ul, .ols-note-card ol { margin: 0; padding-left: 22px; }\n\n    .ols-key-box { margin-top: 20px; background: var(--soft-green); border: 1px solid rgba(63, 143, 70, 0.25); border-radius: 20px; padding: 18px 20px; }\n    .ols-key-box p { margin: 0; font-weight: 400; color: var(--navy); }\n    .ols-definition-box { background: linear-gradient(135deg, #ffffff, var(--soft-purple)); border: 2px dashed rgba(122, 62, 157, 0.35); border-radius: 24px; padding: 22px 24px; margin-top: 22px; }\n    .ols-definition-box p { margin: 0; color: var(--navy); font-weight: 400; }\n\n    .ols-rule-list { display: grid; gap: 14px; margin-top: 18px; }\n    .ols-rule-item { background: #ffffff; border: 1px solid var(--border); border-left: 5px solid var(--blue); border-radius: 18px; padding: 18px; box-shadow: var(--inner-shadow); }\n    .ols-rule-item h3 { margin: 0 0 8px; font-size: 20px; line-height: 1.25; color: var(--navy); }\n    .ols-rule-item p { margin: 0; font-size: 15px; line-height: 1.6; }\n\n    .ols-figure-card { margin: 26px auto 4px; border: 1px solid var(--border); border-radius: 26px; overflow: hidden; background: #ffffff; box-shadow: var(--inner-shadow); max-width: 100%; }\n    .ols-figure-card.medium { max-width: 820px; }\n    .ols-figure-card.compact { max-width: 700px; }\n    .ols-figure-image { width: 100%; min-height: 260px; display: flex; align-items: center; justify-content: center; background: #ffffff; padding: 20px; }\n    .ols-figure-image img { max-width: 100%; height: auto; display: block; }\n    .ols-figure-caption { padding: 18px 24px 22px; background: linear-gradient(135deg, #ffffff, #f8fbff); border-top: 1px solid var(--border); }\n    .ols-figure-caption p { margin: 0; color: #5f6b85; font-size: clamp(15px, 1.3vw, 17px); line-height: 1.6; font-weight: 300; font-style: italic; }\n    .ols-zoom-card, .ols-zoom-card * { box-sizing: border-box; }\n    .ols-zoom-card { display: block !important; margin: 26px auto 34px !important; border: 1px solid rgba(28, 36, 75, 0.14) !important; border-radius: 26px !important; background: #ffffff !important; box-shadow: 0 18px 45px rgba(28, 36, 75, 0.10) !important; overflow: visible !important; position: relative !important; z-index: 1 !important; isolation: isolate !important; }\n    .ols-zoom-card.medium { max-width: 820px; }\n    .ols-zoom-card.compact { max-width: 700px; }\n    .ols-zoom-card.wide { max-width: 940px; }\n    .ols-zoom-card.slim { max-width: 600px; }\n    .ols-zoom-card:hover { z-index: 50 !important; }\n    .ols-zoom-card-image { display: flex !important; align-items: center !important; justify-content: center !important; width: 100% !important; min-height: 240px !important; padding: 20px !important; background: #ffffff !important; overflow: visible !important; border-top-left-radius: 26px !important; border-top-right-radius: 26px !important; position: relative !important; z-index: 2 !important; }\n    .ols-zoom-card img.ols-zoomable-img { display: block !important; max-width: 100% !important; height: auto !important; border-radius: 18px !important; cursor: zoom-in !important; pointer-events: auto !important; user-select: none !important; -webkit-user-drag: none !important; transform: translateZ(0) scale(1) !important; transform-origin: center center !important; transition: transform 0.32s ease, box-shadow 0.32s ease, filter 0.32s ease !important; position: relative !important; z-index: 2 !important; }\n    @media (hover: hover) and (pointer: fine) { .ols-zoom-card img.ols-zoomable-img:hover { transform: translateZ(0) scale(1.35) !important; box-shadow: 0 28px 70px rgba(28, 36, 75, 0.34) !important; filter: saturate(1.02) contrast(1.01) !important; z-index: 100 !important; } }\n    .ols-zoom-card-caption { padding: 18px 22px 20px !important; background: linear-gradient(135deg, #ffffff, #f8fbff) !important; border-bottom-left-radius: 26px !important; border-bottom-right-radius: 26px !important; position: relative !important; z-index: 1 !important; }\n    .ols-zoom-card-caption p { margin: 0 !important; color: #5f6b85 !important; font-size: 15px !important; line-height: 1.65 !important; font-weight: 300 !important; font-style: italic !important; font-family: Poppins, Arial, sans-serif !important; }\n    .ols-image-lightbox { position: fixed; inset: 0; z-index: 999999; display: none; align-items: center; justify-content: center; padding: 34px; background: rgba(10, 15, 35, 0.86); backdrop-filter: blur(8px); -webkit-backdrop-filter: blur(8px); }\n    .ols-image-lightbox.is-open { display: flex; }\n    .ols-image-lightbox-inner { position: relative; width: min(96vw, 1500px); max-height: 92vh; display: flex; align-items: center; justify-content: center; }\n    .ols-image-lightbox-img { display: block; max-width: 100%; max-height: 92vh; height: auto; width: auto; border-radius: 22px; background: #ffffff; box-shadow: 0 32px 90px rgba(0, 0, 0, 0.45); object-fit: contain; }\n    .ols-image-lightbox-close { position: absolute; top: -18px; right: -18px; width: 46px; height: 46px; border: 0; border-radius: 50%; background: #ffffff; color: var(--navy); font-family: Poppins, Arial, sans-serif; font-size: 28px; line-height: 1; font-weight: 700; cursor: pointer; box-shadow: 0 16px 34px rgba(0, 0, 0, 0.28); display: flex; align-items: center; justify-content: center; transition: transform 0.2s ease, background 0.2s ease, color 0.2s ease; }\n    .ols-image-lightbox-close:hover { transform: scale(1.08); background: var(--blue); color: #ffffff; }\n    @media (max-width: 760px) { .ols-zoom-card { border-radius: 22px !important; overflow: hidden !important; } .ols-zoom-card-image { min-height: auto !important; padding: 12px !important; overflow: hidden !important; border-top-left-radius: 22px !important; border-top-right-radius: 22px !important; } .ols-zoom-card img.ols-zoomable-img, .ols-zoom-card img.ols-zoomable-img:hover { transform: none !important; box-shadow: none !important; } .ols-zoom-card-caption { border-bottom-left-radius: 22px !important; border-bottom-right-radius: 22px !important; } .ols-image-lightbox { padding: 16px; } .ols-image-lightbox-inner { width: 100%; max-height: 88vh; } .ols-image-lightbox-img { max-height: 88vh; border-radius: 16px; } .ols-image-lightbox-close { top: 10px; right: 10px; width: 42px; height: 42px; font-size: 26px; } }\n\n\n    .ols-table-wrap { overflow: hidden; border-radius: 22px; border: 1px solid var(--border); background: #ffffff; margin-top: 18px; }\n    .ols-table { width: 100%; border-collapse: collapse; table-layout: fixed; }\n    .ols-table th { background: var(--navy); color: #ffffff; padding: 16px; text-align: left; font-size: clamp(14px, 1.2vw, 17px); font-weight: 600; overflow-wrap: anywhere; }\n    .ols-table td { padding: 16px; border-bottom: 1px solid var(--border); font-size: clamp(14px, 1.15vw, 16px); line-height: 1.45; color: var(--body-text); vertical-align: top; overflow-wrap: anywhere; }\n    .ols-table tr:last-child td { border-bottom: none; }\n\n    .ols-h5p-card { background: linear-gradient(135deg, #ffffff 0%, #f7f0ff 100%); }\n    .ols-h5p-frame { margin-top: 22px; padding: 18px; border-radius: 24px; background: #ffffff; border: 1px solid var(--border); box-shadow: inset 0 0 0 1px rgba(28, 36, 75, 0.03); }\n\n    .ols-faq-list { display: grid; gap: 14px; margin-top: 18px; }\n    .ols-faq-item { background: #ffffff; border: 1px solid var(--border); border-radius: 18px; padding: 18px 20px; box-shadow: var(--inner-shadow); }\n    .ols-faq-item h3 { margin: 0 0 8px; 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text-decoration: none; border-radius: 24px; }\n    .ols-course-cta-image {\n      width: 100%;\n      border-radius: 24px;\n      overflow: hidden;\n      border: 1px solid var(--border);\n      background: #ffffff;\n      box-shadow: var(--inner-shadow);\n      transition: transform 0.35s ease, box-shadow 0.35s ease;\n    }\n    .ols-course-cta-image img { width: 100%; height: auto; display: block; transition: transform 0.45s ease; }\n    .ols-course-cta-image-link:hover .ols-course-cta-image { transform: translateY(-8px) scale(1.015); box-shadow: 0 26px 60px rgba(28, 36, 75, 0.18), 0 0 0 1px rgba(37, 99, 235, 0.12); }\n    .ols-course-cta-image-link:hover .ols-course-cta-image img { transform: scale(1.03); }\n    .ols-course-cta-header-row { display: flex; flex-wrap: wrap; align-items: center; justify-content: space-between; gap: 14px; margin-bottom: 18px; }\n    .ols-course-cta-kicker { display: inline-flex; align-items: center; padding: 8px 14px; border-radius: 999px; background: #ffffff; border: 1px solid rgba(37, 99, 235, 0.18); color: var(--blue); font-size: 14px; line-height: 1.2; font-weight: 700; box-shadow: var(--inner-shadow); }\n    .ols-course-cta-covalent h2 { margin: 0 0 14px; font-size: clamp(28px, 3.5vw, 42px); line-height: 1.15; font-weight: 800; letter-spacing: -0.03em; color: #111827; }\n    .ols-course-cta-intro { margin: 0 0 24px; color: var(--body-text); font-size: clamp(16px, 1.4vw, 18px); line-height: 1.7; font-weight: 300; }\n    .ols-course-cta-features { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 14px; margin: 0 0 30px; }\n    .ols-course-feature { background: rgba(255, 255, 255, 0.78); border: 1px solid var(--border); border-radius: 18px; padding: 16px 18px; }\n    .ols-course-feature h3 { margin: 0 0 6px; color: var(--navy); font-size: 18px; line-height: 1.3; font-weight: 800; }\n    .ols-course-feature p { margin: 0; color: var(--body-text); font-size: 15px; line-height: 1.6; font-weight: 300; }\n    .ols-course-cta-bottom { display: flex; justify-content: center; padding-top: 22px; border-top: 1px solid var(--border); }\n    .ols-course-button { display: inline-flex; align-items: center; justify-content: center; padding: 15px 28px; border-radius: 999px; background: var(--navy); color: #ffffff; text-decoration: none; font-size: 16px; line-height: 1.2; font-weight: 800; box-shadow: 0 12px 26px rgba(28, 36, 75, 0.18); transition: transform 0.2s ease, background 0.2s ease, box-shadow 0.2s ease; }\n    .ols-course-button:hover { transform: translateY(-2px); background: var(--blue); color: #ffffff; box-shadow: 0 16px 32px rgba(37, 99, 235, 0.24); }\n    .ols-course-button-top { flex-shrink: 0; padding: 12px 22px; font-size: 15px; }\n\n    .ols-attribution-card {\n      background: linear-gradient(135deg, #ffffff, #f8fbff);\n      border: 1px solid rgba(28, 36, 75, 0.14);\n      border-radius: 28px;\n      box-shadow: 0 18px 45px rgba(28, 36, 75, 0.10);\n      padding: 34px;\n      margin-bottom: 24px;\n      overflow: hidden;\n      font-family: Poppins, Arial, sans-serif;\n      box-sizing: border-box;\n    }\n    .ols-attribution-card, .ols-attribution-card * { box-sizing: border-box; }\n    .ols-attribution-card p { margin: 0; font-size: 14px; line-height: 1.65; font-weight: 300; color: #667085; }\n    .ols-attribution-card strong { font-weight: 700; color: #1C244B; }\n\n    @media (max-width: 1050px) {\n      .ols-main { max-width: none; }\n      .ols-related-grid { grid-template-columns: repeat(2, minmax(0, 1fr)); }\n      .ols-course-cta-top { grid-template-columns: 1fr; }\n      .ols-course-cta-image-link { max-width: 520px; margin: 0 auto; }\n    }\n\n    @media (max-width: 760px) {\n      .ols-title-card, .ols-note-card, .ols-h5p-card, .ols-related-card, .ols-faq-card, .ols-attribution-card { padding: 24px 18px; border-radius: 22px; }\n      .ols-note-title { align-items: flex-start; }\n      .ols-related-grid, .ols-course-cta-features { grid-template-columns: 1fr; }\n      .ols-figure-card { border-radius: 22px; }\n      .ols-figure-image { min-height: 210px; padding: 14px; }\n      .ols-figure-caption { padding: 16px; }\n      .ols-table-wrap { border: none; 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}\n      .ols-course-cta-card { padding: 20px; border-radius: 24px; }\n      .ols-course-cta-header-row { align-items: stretch; }\n      .ols-course-button-top, .ols-course-button { width: 100%; }\n    }\n  \n    .ols-figure-placeholder .ols-placeholder-box { border: 2px dashed #c9973a; background: #fffaf0; border-radius: 16px; padding: 26px 22px; font-weight: 700; color: #7a4b12; text-align: center; line-height: 1.6; }\n    .ols-figure-placeholder .ols-figure-image { background: transparent; }\n    .ols-figure-placeholder { background: #ffffff; border: 1px solid rgba(28, 36, 75, 0.12); border-radius: 22px; padding: 14px; margin: 18px 0 6px; }\n    .ols-figure-placeholder .ols-figure-caption p { margin: 10px 0 0; font-size: 14px; color: #667085; text-align: center; }\n\n    \/* inline checks (H5P re-flow, Sep 2026) *\/\n    .ols-h5p-card.ols-h5p-inline { padding: 26px 28px; border-left: 6px solid #7c3aed; }\n    .ols-h5p-card.ols-h5p-inline h2 { font-size: clamp(20px, 2.2vw, 27px); letter-spacing: -0.02em; }\n    .ols-h5p-card.ols-h5p-inline > p { margin: 8px 0 0; }\n    .ols-h5p-card.ols-h5p-inline .ols-h5p-frame { margin-top: 16px; padding: 14px; border-radius: 20px; }\n    .ols-h5p-kicker { display: inline-block; margin-bottom: 10px; padding: 5px 12px; border-radius: 999px; background: #ede9fe; color: #5b21b6; font-size: 12px; font-weight: 700; letter-spacing: 0.06em; text-transform: uppercase; }\n    .ols-h5p-card.ols-h5p-recap { border-left-color: #c9973a; background: linear-gradient(135deg, #ffffff 0%, #fff8e8 100%); }\n    .ols-h5p-recap .ols-h5p-kicker { background: #fdf0d2; color: #8a5a00; }\n    @media (max-width: 760px) { .ols-h5p-card.ols-h5p-inline { padding: 20px 16px; } }\n\n    \/* core practical pages (Sep 2026) *\/\n    .ols-note-card h3 { margin: 22px 0 8px; font-size: 18px; line-height: 1.25; font-weight: 500; color: var(--navy); }\n    .ols-table td { overflow-wrap: anywhere; }\n<\/style>\n\n  <aside class=\"ols-sidebar\">\n  <div class=\"ols-sidebar-header\">\n    <h3>Revision Notes<\/h3>\n    <p>AQA A Level Chemistry<\/p>\n  <\/div>\n\n  <div class=\"ols-topic-group\">\n    <h4>Required Practicals<\/h4>\n\n    <ul class=\"ols-topic-list\">\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/required-practicals\/molar-volume-of-a-gas\/\">Gas volumes: Molar Volume of a Gas<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/required-practicals\/rp2-measurement-of-an-enthalpy-change\/\">RP2: Enthalpy Change via Hess's Law<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/required-practicals\/rp1-acid-base-titration\/\">RP1: Concentration of HCl by Titration<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/required-practicals\/rp1-making-a-volumetric-solution\/\">RP1: Preparation of a Standard Solution<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/required-practicals\/rates-of-hydrolysis-of-halogenoalkanes\/\">Hydrolysis rates: Hydrolysis of Halogenoalkanes<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/required-practicals\/preparing-an-organic-liquid-chlorination-of-2-methylpropan-2-ol\/\">Organic prep: Chlorination of 2-methylpropan-2-ol<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/required-practicals\/rp5-distillation-of-a-product-oxidation-of-ethanol\/\">RP5: Oxidation of an Alcohol<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/required-practicals\/rp4-rp6-identifying-inorganic-ions-and-organic-functional-groups\/\">RP4 and RP6: Analysis of Inorganic and Organic Unknowns<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/required-practicals\/rp3-effect-of-temperature-on-rate-of-reaction\/\">RP3: Rates of Reaction<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/required-practicals\/gravimetric-analysis-water-of-crystallisation\/\">Gravimetric: Gravimetric and Composition Analysis<\/a>\n      <\/li>\n    <\/ul>\n  <\/div>\n\n  <div class=\"ols-topic-group\">\n    <h4>Useful Links<\/h4>\n\n    <ul class=\"ols-topic-list\">\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/\">AQA Chemistry<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/required-practicals\/\">Required Practicals<\/a>\n      <\/li>\n    <\/ul>\n  <\/div>\n<\/aside>\n\n<script>\ndocument.addEventListener('DOMContentLoaded', function () {\n  var currentPath = window.location.pathname.replace(\/\\\/$\/, '');\n  var sidebarLinks = document.querySelectorAll('.ols-sidebar .ols-topic-list a');\n  sidebarLinks.forEach(function (link) {\n    var linkPath = new URL(link.href, window.location.origin).pathname.replace(\/\\\/$\/, '');\n    if (linkPath === currentPath) { link.closest('li').classList.add('active'); } else { link.closest('li').classList.remove('active'); }\n  });\n});\n<\/script>\n\n  <main class=\"ols-main\">\n      <nav class=\"ols-breadcrumbs\" 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\/aqa\/\">AQA<\/a> \/\n<a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/required-practicals\/\">Required Practicals<\/a> \/\n<span>Comparing the Rates of Hydrolysis of Halogenoalkanes<\/span>\n<\/nav>\n\n      <header class=\"ols-title-card\">\n        <h1>Comparing the Rates of Hydrolysis of Halogenoalkanes<\/h1>\n        <p class=\"ols-page-intro\">In Practical Skills: Rates of Hydrolysis you compare how quickly halogenoalkanes are hydrolysed by timing the appearance of a silver halide precipitate after aqueous silver nitrate is added. Relative rate is 1\/t, so a shorter time means a faster reaction. Part 1 changes the halogen; Part 2 changes the structure around the carbon bonded to the halogen.<\/p>\n\n        <div class=\"ols-badges\">\n<div class=\"ols-badge\">Paper 1, 2 and 3<\/div>\n<div class=\"ols-badge\">AQA<\/div>\n<div class=\"ols-badge\">Practical Skills: Rates of Hydrolysis<\/div>\n<div class=\"ols-badge\">7405<\/div>\n<\/div>\n\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:<br><span>Dr. Mohammed Al-Fatah<\/span>\n      <\/h2>\n\n      <p class=\"ols-author-description\">Chemistry specialist revision notes for AQA A Level Chemistry.<\/p>\n\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\"\/>\n        <\/svg>\n        View LinkedIn Profile\n      <\/a>\n\n    <\/div>\n\n  <\/div>\n      <\/header>\n\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: Testing for Halide Ions<\/h2>\n<p>Three quick questions on the silver nitrate test you met at GCSE: the colours, the reason for the acid and what a precipitate is.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-content\" data-content-id=\"1008\"><\/div><\/div>\n<\/section>\n<article class=\"ols-note-card\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">1<\/div>\n<h2>What This Practical Is Testing<\/h2>\n<\/div>\n<p>In this practical (Practical Skills: Rates of Hydrolysis) you compare how quickly different halogenoalkanes are <strong>hydrolysed<\/strong>.<\/p><p>Hydrolysis is a reaction with water: the water molecule acts as a nucleophile, the C\u2013X bond breaks and the products are an <strong>alcohol, a hydrogen ion and a halide ion<\/strong>.<\/p><p>The halide ion is detected by aqueous silver nitrate, which gives a precipitate of the silver halide. The rates are compared by timing how long the precipitate takes to appear.<\/p><div class=\"ols-key-box\"><p><strong>Key idea:<\/strong> <strong>relative rate \u221d 1\/t<\/strong>, so a shorter time means a faster hydrolysis. The experiment gives relative rates, not a rate in mol dm\u207b\u00b3 s\u207b\u00b9.<\/p><\/div>\n<p>The experiment has two linked comparisons. In <strong>Part 1<\/strong> three primary halogenoalkanes with different halogens are compared: 1-chlorobutane, 1-bromobutane and 1-iodobutane.<\/p>\n<p>In <strong>Part 2<\/strong> the halogen is kept the same and the structure is changed: 1-bromobutane (primary), 2-bromobutane (secondary) and 2-bromo-2-methylpropane (tertiary).<\/p>\n<p>The chemistry is examined in the written papers (at least 15% of the marks test practical skills) and the practical endorsement.<\/p>\n<p>Expect to describe the method, explain the role of each reagent, process the times and explain the order using bond enthalpies from the AQA data sheet.<\/p>\n<div class=\"ols-table-wrap\">\n<table class=\"ols-table\">\n<thead>\n<tr><th>Stage<\/th><th>What happens<\/th><th>What you see<\/th><\/tr>\n<\/thead>\n<tbody>\n<tr><td><strong>Hydrolyse<\/strong><\/td><td>Water attacks the halogenoalkane; the C\u2013X bond breaks and X\u207b is released.<\/td><td>Nothing yet: the solution stays clear.<\/td><\/tr>\n<tr><td><strong>Detect<\/strong><\/td><td>Ag\u207a(aq) from the silver nitrate reacts with X\u207b(aq) to give AgX(s).<\/td><td>The liquid turns cloudy throughout.<\/td><\/tr>\n<tr><td><strong>Compare<\/strong><\/td><td>The time to the first cloudiness is recorded and converted to 1\/t.<\/td><td>The shortest time is the fastest hydrolysis.<\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<div class=\"ols-key-box\">\n<p><strong>Key idea:<\/strong> Silver nitrate does not cause the hydrolysis. The water it is dissolved in is the nucleophile, and the Ag\u207a ions detect the halide ion as it is released.<\/p><p>This is why no precipitate can form before the aqueous silver nitrate is added, and why timing starts at that moment.<\/p>\n<\/div>\n<\/article>\n<article class=\"ols-note-card soft\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">2<\/div>\n<h2>Safety and Apparatus<\/h2>\n<\/div>\n<p>The reagents are flammable, volatile and, in the case of silver nitrate, staining. A hazard question expects you to name the hazard and the matching precaution, not just &#8220;wear goggles&#8221;.<\/p>\n<div class=\"ols-table-wrap\">\n<table class=\"ols-table\">\n<thead>\n<tr><th>Apparatus or reagent<\/th><th>What it is for<\/th><th>Note<\/th><\/tr>\n<\/thead>\n<tbody>\n<tr><td><strong>250 cm\u00b3 beaker<\/strong><\/td><td>Water bath, three-quarters full<\/td><td>Filled from a kettle, never heated with a Bunsen<\/td><\/tr>\n<tr><td><strong>Thermometer (0 to 100 \u00b0C)<\/strong><\/td><td>Checks the bath is at 50 \u00b0C before and during timing<\/td><td>Reads to \u00b10.5 \u00b0C<\/td><\/tr>\n<tr><td><strong>Test tubes with bungs<\/strong><\/td><td>Hold 5 cm\u00b3 ethanol + 4 drops of halogenoalkane; the bung stops the volatile halogenoalkane escaping while the tube warms<\/td><td>2-bromo-2-methylpropane boils at 73 \u00b0C<\/td><\/tr>\n<tr><td><strong>Dropping pipettes<\/strong><\/td><td>Deliver the drops of halogenoalkane and the 1 cm\u00b3 of silver nitrate<\/td><td>One pipette per liquid to avoid contamination<\/td><\/tr>\n<tr><td><strong>Measuring cylinder or graduated pipette<\/strong><\/td><td>Measures 5 cm\u00b3 ethanol and 1 cm\u00b3 silver nitrate solution<\/td><td>1 cm\u00b3 graduated pipette reads to \u00b10.05 cm\u00b3<\/td><\/tr>\n<tr><td><strong>Stop clock<\/strong><\/td><td>Times from adding the silver nitrate to the first cloudiness<\/td><td>Reads to 0.01 s; reaction time is the real limit<\/td><\/tr>\n<tr><td><strong>White tile or card<\/strong><\/td><td>Background against which the first cloudiness is judged<\/td><td>Same background for every tube<\/td><\/tr>\n<tr><td><strong>Reagents<\/strong><\/td><td>1-chlorobutane, 1-bromobutane, 1-iodobutane, 2-bromobutane, 2-bromo-2-methylpropane, ethanol, 0.05 mol dm\u207b\u00b3 silver nitrate solution<\/td><td>Kettle for the hot water<\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<div class=\"ols-key-box\">\n<p><strong>Hazards and precautions:<\/strong> Ethanol and the halogenoalkanes are highly flammable: no naked flames, so the water bath is prepared from a kettle.<\/p><p>The halogenoalkanes are harmful and volatile: work in a well ventilated laboratory or fume cupboard and keep the tubes stoppered until the silver nitrate is added.<\/p><p>Silver nitrate stains skin and is an irritant: wear gloves and wash spills off at once.<\/p><p>Kettle water scalds: mix it with cold water to reach 50 \u00b0C before filling the beaker. Eye protection throughout.<\/p>\n<\/div>\n<\/article>\n<article class=\"ols-note-card\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">3<\/div>\n<h2>The Five Halogenoalkanes Used<\/h2>\n<\/div>\n<p>Before you interpret the results you must be able to classify each halogenoalkane.<\/p><p>Find the carbon atom bonded to the halogen and <strong>count the carbon atoms bonded to that carbon<\/strong>: one gives a primary halogenoalkane, two a secondary and three a tertiary.<\/p><div class=\"ols-key-box\"><p><strong>Remember:<\/strong> The length of the chain is irrelevant; only the environment of the C\u2013X carbon counts.<\/p><\/div>\n<div class=\"ols-table-wrap\">\n<table class=\"ols-table\">\n<thead>\n<tr><th>Halogenoalkane<\/th><th>Classification<\/th><th>Where it is used<\/th><th>Comparison being made<\/th><\/tr>\n<\/thead>\n<tbody>\n<tr><td><strong>1-chlorobutane<\/strong><\/td><td>Primary<\/td><td>Part 1<\/td><td>Effect of the halogen<\/td><\/tr>\n<tr><td><strong>1-bromobutane<\/strong><\/td><td>Primary<\/td><td>Parts 1 and 2<\/td><td>Control compound in both parts<\/td><\/tr>\n<tr><td><strong>1-iodobutane<\/strong><\/td><td>Primary<\/td><td>Part 1<\/td><td>Effect of the halogen<\/td><\/tr>\n<tr><td><strong>2-bromobutane<\/strong><\/td><td>Secondary<\/td><td>Part 2<\/td><td>Effect of structure<\/td><\/tr>\n<tr><td><strong>2-bromo-2-methylpropane<\/strong><\/td><td>Tertiary<\/td><td>Part 2<\/td><td>Effect of structure<\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<p>1-Bromobutane appears in both parts on purpose. In Part 1 it is the middle member of the halogen series; in Part 2 it is the primary compound against which the secondary and tertiary bromoalkanes are judged.<\/p><p>The tertiary compound is the bromo analogue of 2-chloro-2-methylpropane, the product prepared in <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/required-practicals\/preparing-an-organic-liquid-chlorination-of-2-methylpropan-2-ol\/\">Practical Skills: Organic Preparation (chlorination of 2-methylpropan-2-ol)<\/a>.<\/p>\n<div class=\"ols-zoom-card\">\n<div class=\"ols-zoom-card-image\">\n<a class=\"ols-lightbox-link\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/09\/core-practical-hyd-classify.jpg\" aria-label=\"Open image full screen\">\n<img decoding=\"async\" class=\"ols-zoomable-img ols-lightbox-target\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/09\/core-practical-hyd-classify.jpg\" alt=\"Skeletal formulas of 1-chlorobutane, 1-bromobutane and 1-iodobutane (primary), 2-bromobutane (secondary) and 2-bromo-2-methylpropane (tertiary), with the carbon carrying the halogen ringed\">\n<\/a>\n<\/div>\n<div class=\"ols-zoom-card-caption\"><p>Skeletal formulae of the five halogenoalkanes with the carbon bonded to the halogen circled. Three are primary, one is secondary and one is tertiary.<\/p><\/div>\n<\/div>\n<div class=\"ols-key-box\">\n<p><strong>Exam wording:<\/strong> &#8220;The carbon bonded to the bromine is attached to three other carbon atoms, so 2-bromo-2-methylpropane is a tertiary halogenoalkane.&#8221; Name the carbon, count its neighbours, state the class.<\/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>Check: Classifying by the C\u2013X Carbon<\/h2>\n<p>Classify six halogenoalkanes that are not on this page as primary, secondary or tertiary.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-1009\" class=\"h5p-iframe\" data-content-id=\"1009\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Rates of Hydrolysis Quick Choice: Classifying by the C\u2013X Carbon\"><\/iframe><\/div><\/div>\n<\/section>\n<article class=\"ols-note-card\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">4<\/div>\n<h2>Method: Step by Step<\/h2>\n<\/div>\n<p>The reaction runs in a water bath at about <strong>50 \u00b0C<\/strong>. At room temperature 1-chlorobutane takes far too long to give a visible precipitate (the sample time below is already 10 minutes at 50 \u00b0C).<\/p>\n<p>A controlled temperature is essential because rate depends on temperature. Every step below carries its reason: the reason is what the mark scheme rewards.<\/p>\n<div class=\"ols-table-wrap\">\n<table class=\"ols-table\">\n<thead>\n<tr><th>Step<\/th><th>What you do<\/th><th>Why<\/th><\/tr>\n<\/thead>\n<tbody>\n<tr><td><strong>1 Prepare the bath<\/strong><\/td><td>Fill a 250 cm\u00b3 beaker about three-quarters full with water from a kettle mixed with cold water, and check with a thermometer that it reads 50 \u00b0C.<\/td><td>No naked flames near flammable ethanol and halogenoalkanes; the temperature must be known and kept the same for every tube.<\/td><\/tr>\n<tr><td><strong>2 Add ethanol<\/strong><\/td><td>Add 5 cm\u00b3 of ethanol to each labelled test tube.<\/td><td>Ethanol is a solvent in which both the halogenoalkane and the aqueous silver nitrate mix, giving one phase so that water molecules can reach the halogenoalkane.<\/td><\/tr>\n<tr><td><strong>3 Add the halogenoalkane<\/strong><\/td><td>Add four drops of the relevant halogenoalkane to its tube and bung it.<\/td><td>The same number of drops gives approximately equal amounts; the bung stops the volatile halogenoalkane evaporating while the tube warms.<\/td><\/tr>\n<tr><td><strong>4 Warm both reagents<\/strong><\/td><td>Stand the halogenoalkane tubes and a tube of 0.05 mol dm\u207b\u00b3 silver nitrate solution in the same bath for a few minutes.<\/td><td>Both reagents must be at 50 \u00b0C when mixed; otherwise the mixture cools on mixing and the temperature is not controlled.<\/td><\/tr>\n<tr><td><strong>5 Mix and start the clock<\/strong><\/td><td>Add 1 cm\u00b3 (the same volume in every tube) of the warmed silver nitrate solution, bung, shake once and start the stop clock immediately.<\/td><td>The water in the aqueous silver nitrate is the nucleophile, so hydrolysis begins the moment it is added; the same volume keeps the Ag\u207a and water concentrations equal.<\/td><\/tr>\n<tr><td><strong>6 Judge the first cloudiness<\/strong><\/td><td>Keep the tube in the bath and watch it against a white tile; stop the clock at the first sign of cloudiness.<\/td><td>The precipitate is a fine suspension, so &#8220;first cloudiness&#8221; against a fixed background is the endpoint; taking the tube out lets it cool.<\/td><\/tr>\n<tr><td><strong>7 Repeat and record<\/strong><\/td><td>Repeat each tube, discard anomalous times and calculate a mean; record the colour of each precipitate.<\/td><td>Judging cloudiness is the main random error; a mean of concordant times reduces it and the colour confirms which halide was released.<\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<p>The <strong>control variables<\/strong> an examiner expects you to list are: the temperature of the bath, the volume of ethanol, the volume and concentration of the silver nitrate solution, and the amount of halogenoalkane.<\/p><p>Two more are the same observer judging the endpoint against the same background, and the tubes staying in the bath throughout. The only variable that changes is the halogenoalkane.<\/p>\n<div class=\"ols-zoom-card\">\n<div class=\"ols-zoom-card-image\">\n<a class=\"ols-lightbox-link\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/09\/core-practical-hyd-apparatus.jpg\" aria-label=\"Open image full screen\">\n<img decoding=\"async\" class=\"ols-zoomable-img ols-lightbox-target\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/09\/core-practical-hyd-apparatus.jpg\" alt=\"Water bath at 50 \u00b0C with three reagent tubes, the silver nitrate tube, pipette, stop clock and white tile\">\n<\/a>\n<\/div>\n<div class=\"ols-zoom-card-caption\"><p>The timing set-up: bath at 50 \u00b0C with a thermometer, three reagent tubes and the warmed silver nitrate, a pipette delivering 1 cm\u00b3, a stop clock and a white tile behind the tubes.<\/p><\/div>\n<\/div>\n<div class=\"ols-key-box\">\n<p><strong>Evaluation point:<\/strong> Using the same number of drops of each liquid gives approximately, not exactly, equal amounts of substance: the halogenoalkanes have different densities and molar masses. A fairer method measures equal moles by mass or with a graduated pipette.<\/p>\n<\/div>\n<\/article>\n<!-- 3D card: hydrolysis-timing (27 Sep 2026) -->\n<!-- Copyright (c) 2026 Dr. Mohammed Al-Fatah, onlinelearningsystem.net. 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The halogen is more electronegative than carbon, so the C\u2013X bond is polar and the carbon carries a partial positive charge, \u03b4+.<\/p><p>Water is a nucleophile because its oxygen atom has two lone pairs of electrons.<\/p><p>In the primary halogenoalkanes of Part 1 the oxygen lone pair attacks the \u03b4+ carbon while the C\u2013X bond breaks, the halide ion leaves and the protonated alcohol then loses H\u207a.<\/p>\n<p>R\u2013X + H\u2082O \u2192 R\u2013OH + H\u207a + X\u207b<\/p>\n<p>CH\u2083CH\u2082CH\u2082CH\u2082Br(l) + H\u2082O(l) \u2192 CH\u2083CH\u2082CH\u2082CH\u2082OH(aq) + H\u207a(aq) + Br\u207b(aq)<\/p>\n<p>Water is a <strong>weak nucleophile<\/strong>, much weaker than hydroxide ions, which is why the reaction is slow enough to time with a stop clock. Direct attack on the \u03b4+ carbon is not the only route, and this matters for Part 2.<\/p>\n<p>The two routes have names. A primary halogenoalkane reacts mainly by the <strong>S\u20992 mechanism<\/strong>: water attacks the \u03b4+ carbon and the C\u2013X bond breaks in the same step.<\/p><p>A tertiary halogenoalkane reacts mainly by the <strong>S\u20991 mechanism<\/strong>: the C\u2013X bond breaks first to give a carbocation, and water attacks the carbocation in a second, fast step.<\/p><p>The tertiary carbocation, (CH\u2083)\u2083C\u207a, is stabilised by the <strong>positive inductive effect<\/strong> of three alkyl groups pushing electron density towards the positive carbon, so it forms readily and 2-bromo-2-methylpropane hydrolyses fastest. A secondary halogenoalkane sits between the two.<\/p>\n<div class=\"ols-zoom-card\">\n<div class=\"ols-zoom-card-image\">\n<a class=\"ols-lightbox-link\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/09\/skel-67-cp5-hydrolysis-mechanism.svg\" aria-label=\"Open image full screen\">\n<img decoding=\"async\" class=\"ols-zoomable-img ols-lightbox-target\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/09\/skel-67-cp5-hydrolysis-mechanism.svg\" alt=\"Mechanism of the hydrolysis of 1-bromobutane by water to give butan-1-ol, with curly arrows and lone pairs\" width=\"1503\" height=\"1643\">\n<\/a>\n<\/div>\n<div class=\"ols-zoom-card-caption\"><p>Water attacks the \u03b4+ carbon of a primary halogenoalkane in one step as the C\u2013Br bond breaks; the protonated alcohol then loses H\u207a.<\/p><\/div>\n<\/div>\n<div class=\"ols-key-box\">\n<p><strong>Key idea:<\/strong> Whatever the route, the C\u2013X bond must break. In Part 1 the strength of that bond controls the rate; in Part 2 the halogen is the same, so the stability of the carbocation that can form controls the rate.<\/p>\n<\/div>\n<\/article>\n<article class=\"ols-note-card\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">6<\/div>\n<h2>Why Ethanol, Water and Silver Nitrate Are Used<\/h2>\n<\/div>\n<p>Each reagent has one job, and students lose marks by swapping them round: the commonest error is calling ethanol the nucleophile.<\/p>\n<div class=\"ols-table-wrap\">\n<table class=\"ols-table\">\n<thead>\n<tr><th>Reagent<\/th><th>Role<\/th><th>Why it matters<\/th><\/tr>\n<\/thead>\n<tbody>\n<tr><td><strong>Ethanol<\/strong><\/td><td>Solvent in which both the halogenoalkane and the aqueous silver nitrate dissolve<\/td><td>Halogenoalkanes are almost insoluble in water; without ethanol there would be two layers and the water could not reach the halogenoalkane.<\/td><\/tr>\n<tr><td><strong>Water (in the aqueous silver nitrate)<\/strong><\/td><td>The nucleophile that attacks the \u03b4+ carbon<\/td><td>It is the only source of water in the tube, so no hydrolysis, and no precipitate, can occur before it is added.<\/td><\/tr>\n<tr><td><strong>Silver nitrate<\/strong><\/td><td>Supplies Ag\u207a(aq) to detect the halide ion as AgX(s)<\/td><td>The precipitate makes an invisible reaction visible; its colour tells you which halide was released.<\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<p><strong>Why not use hydroxide ions?<\/strong> Aqueous sodium hydroxide would hydrolyse the halogenoalkane faster, but OH\u207b would give a brown precipitate of silver oxide, Ag\u2082O, the moment silver nitrate was added: 2Ag\u207a(aq) + 2OH\u207b(aq) \u2192 Ag\u2082O(s) + H\u2082O(l).<\/p><p>That masks the halide test. OH\u207b is also a much stronger nucleophile, so the reaction would be over too quickly to time.<\/p>\n<div class=\"ols-key-box\">\n<p><strong>Exam wording:<\/strong> &#8220;Water, from the aqueous silver nitrate, is the nucleophile. Ethanol is the solvent that allows the halogenoalkane and the aqueous solution to mix.&#8221; Never write &#8220;ethanol is the nucleophile&#8221; or &#8220;silver nitrate hydrolyses the halogenoalkane&#8221;.<\/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>Check: Roles of the Reagents<\/h2>\n<p>Fill the gaps for the hydrolysis of a compound not used on this page: nucleophile, solvent, detector and the colour you would see.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-1011\" class=\"h5p-iframe\" data-content-id=\"1011\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Rates of Hydrolysis Fill In: Roles of the Reagents\"><\/iframe><\/div><\/div>\n<\/section>\n<article class=\"ols-note-card soft\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">7<\/div>\n<h2>How the Silver Halide Precipitate Shows the Rate<\/h2>\n<\/div>\n<p>The precipitate can only form once hydrolysis has released halide ions, so the time to the first cloudiness measures how quickly the halogenoalkane has hydrolysed.<\/p>\n<p>Because Ag\u207a(aq) and X\u207b(aq) react instantly, the precipitation step adds nothing to the time.<\/p>\n<p>The solid forms as a <strong>fine suspension<\/strong> throughout the liquid, which is why the endpoint is described as cloudiness rather than a lump at the bottom of the tube.<\/p>\n<div class=\"ols-table-wrap\">\n<table class=\"ols-table\">\n<thead>\n<tr><th>Halide ion released<\/th><th>Ionic equation<\/th><th>Colour of AgX(s)<\/th><th>What it tells you<\/th><\/tr>\n<\/thead>\n<tbody>\n<tr><td><strong>Cl\u207b<\/strong><\/td><td>Ag\u207a(aq) + Cl\u207b(aq) \u2192 AgCl(s)<\/td><td>White<\/td><td>A chloroalkane has hydrolysed<\/td><\/tr>\n<tr><td><strong>Br\u207b<\/strong><\/td><td>Ag\u207a(aq) + Br\u207b(aq) \u2192 AgBr(s)<\/td><td>Cream<\/td><td>A bromoalkane has hydrolysed<\/td><\/tr>\n<tr><td><strong>I\u207b<\/strong><\/td><td>Ag\u207a(aq) + I\u207b(aq) \u2192 AgI(s)<\/td><td>Yellow<\/td><td>An iodoalkane has hydrolysed<\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<p>White and cream are hard to tell apart in a cloudy tube, and the colour is not what the practical measures: the compounds are known, so the colour is a check, not an identification.<\/p><p>The ammonia confirmation that separates them is given in its own card below and in <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/required-practicals\/rp4-rp6-identifying-inorganic-ions-and-organic-functional-groups\/\">Required Practicals 4 and 6 (analysis of inorganic and organic unknowns)<\/a>.<\/p>\n<div class=\"ols-zoom-card\">\n<div class=\"ols-zoom-card-image\">\n<a class=\"ols-lightbox-link\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/09\/core-practical-hyd-precip.jpg\" aria-label=\"Open image full screen\">\n<img decoding=\"async\" class=\"ols-zoomable-img ols-lightbox-target\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/09\/core-practical-hyd-precip.jpg\" alt=\"Three tubes of uniform cloudy suspension, white AgCl, cream AgBr, pale yellow AgI, with the three ionic equations\">\n<\/a>\n<\/div>\n<div class=\"ols-zoom-card-caption\"><p>Silver halide precipitate colours: uniform cloudy suspensions of white silver chloride, cream silver bromide and pale yellow silver iodide, with the ionic equations.<\/p><\/div>\n<\/div>\n<div class=\"ols-key-box\">\n<p><strong>Key idea:<\/strong> Yellow AgI means iodide ions were released by hydrolysis, so the original compound was an iodo compound. It does not mean iodine molecules, I\u2082, are present.<\/p>\n<\/div>\n<\/article>\n<article class=\"ols-note-card\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">8<\/div>\n<h2>Part 1: Comparing Chloro-, Bromo- and Iodoalkanes<\/h2>\n<\/div>\n<p>In Part 1 all three halogenoalkanes are primary, so the only variable is the halogen. The sample results below are for one run at 50 \u00b0C. The column that examiners look for is <strong>1\/t<\/strong>: relative rate is proportional to 1\/t, so the largest value is the fastest reaction.<\/p>\n<div class=\"ols-table-wrap\">\n<table class=\"ols-table\">\n<thead>\n<tr><th>Halogenoalkane<\/th><th>Bond broken<\/th><th>Time to first cloudiness \/ s<\/th><th>1\/t \/ s\u207b\u00b9 (2 s.f.)<\/th><th>Mean bond enthalpy \/ kJ mol\u207b\u00b9<\/th><th>Relative rate<\/th><\/tr>\n<\/thead>\n<tbody>\n<tr><td><strong>1-iodobutane<\/strong><\/td><td>C\u2013I<\/td><td>52<\/td><td>0.019<\/td><td>228<\/td><td>Fastest<\/td><\/tr>\n<tr><td><strong>1-bromobutane<\/strong><\/td><td>C\u2013Br<\/td><td>87<\/td><td>0.011<\/td><td>290<\/td><td>Intermediate<\/td><\/tr>\n<tr><td><strong>1-chlorobutane<\/strong><\/td><td>C\u2013Cl<\/td><td>606<\/td><td>0.0017<\/td><td>346<\/td><td>Slowest<\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<p>The order is iodo > bromo > chloro. The <strong>mean bond enthalpy<\/strong> falls down Group 7: C\u2013Cl 346 kJ mol\u207b\u00b9, C\u2013Br 290 kJ mol\u207b\u00b9, C\u2013I 228 kJ mol\u207b\u00b9 (values from the AQA data sheet).<\/p>\n<p>The C\u2013X bond is broken in the rate-determining step, so the weakest bond, C\u2013I, needs the <strong>lowest activation energy<\/strong> and 1-iodobutane hydrolyses fastest.<\/p>\n<p>The ratio of the 1\/t values shows the size of the effect: 1-iodobutane reacts about 0.019 \/ 0.0017 \u2248 11 times faster than 1-chlorobutane at 50 \u00b0C.<\/p>\n<p>Bond polarity predicts the opposite. Chlorine is the most electronegative of the three halogens, so the C\u2013Cl bond is the most polar and its carbon the most \u03b4+; if polarity controlled the rate the chloro compound would be fastest.<\/p><div class=\"ols-key-box\"><p><strong>Key idea:<\/strong> The data show it is slowest, so <strong>bond enthalpy, not polarity, controls the rate<\/strong>.<\/p><\/div>\n<div class=\"ols-key-box\">\n<p><strong>Exam wording:<\/strong> &#8220;The C\u2013I bond has the lowest bond enthalpy (228 kJ mol\u207b\u00b9), so it breaks most easily in the rate-determining step and 1-iodobutane hydrolyses fastest.&#8221; Quote the values, say which step the bond breaks in, and link weak bond to low activation energy.<\/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>Check: New Data at 50 \u00b0C<\/h2>\n<p>Times for three propyl compounds you have not met on this page: convert to 1\/t, rank, explain and predict the effect of a cooler bath.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-1012\" class=\"h5p-iframe\" data-content-id=\"1012\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Rates of Hydrolysis Work It Out: New Data at 50 \u00b0C\"><\/iframe><\/div><\/div>\n<\/section>\n<article class=\"ols-note-card\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">9<\/div>\n<h2>Part 2: Comparing Primary, Secondary and Tertiary Bromoalkanes<\/h2>\n<\/div>\n<p>In Part 2 the halogen is kept the same, bromine, so the only variable is the structure around the C\u2013Br carbon.<\/p><p>Part 2 was a separate run, which is why 1-bromobutane appears again as the primary control: times are only comparable within one run, so each part carries its own 1-bromobutane reading (87 s in the Part 1 run, 59 s in this one).<\/p><div class=\"ols-key-box\"><p><strong>Remember:<\/strong> Never compare a Part 1 time with a Part 2 time.<\/p><\/div>\n<div class=\"ols-table-wrap\">\n<table class=\"ols-table\">\n<thead>\n<tr><th>Halogenoalkane<\/th><th>Classification<\/th><th>Time to first cloudiness \/ s<\/th><th>1\/t \/ s\u207b\u00b9 (2 s.f.)<\/th><th>Relative rate<\/th><\/tr>\n<\/thead>\n<tbody>\n<tr><td><strong>2-bromo-2-methylpropane<\/strong><\/td><td>Tertiary<\/td><td>3<\/td><td>0.33<\/td><td>Fastest<\/td><\/tr>\n<tr><td><strong>2-bromobutane<\/strong><\/td><td>Secondary<\/td><td>34<\/td><td>0.029<\/td><td>Intermediate<\/td><\/tr>\n<tr><td><strong>1-bromobutane<\/strong><\/td><td>Primary<\/td><td>59<\/td><td>0.017<\/td><td>Slowest<\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<p>The order is <strong>tertiary > secondary > primary<\/strong>, and it needs an explanation because bond enthalpy cannot give one: every compound here has a C\u2013Br bond of about 290 kJ mol\u207b\u00b9.<\/p>\n<p>If water simply attacked the \u03b4+ carbon in every case, the crowded tertiary carbon should be the slowest. It is the fastest because it reacts by a different route.<\/p>\n<p>The C\u2013Br bond breaks first to give the tertiary carbocation (CH\u2083)\u2083C\u207a, which is stabilised by the positive inductive effect of its three alkyl groups, and water then attacks the carbocation.<\/p>\n<div class=\"ols-key-box\"><p><strong>Key idea:<\/strong> The more alkyl groups on the C\u2013Br carbon, the more stable the carbocation, the lower the activation energy and the faster the hydrolysis.<\/p><\/div>\n\n<div class=\"ols-zoom-card\">\n<div class=\"ols-zoom-card-image\">\n<a class=\"ols-lightbox-link\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/09\/skel-06-bromoalkane-rates.svg\" aria-label=\"Open image full screen\">\n<img decoding=\"async\" class=\"ols-zoomable-img ols-lightbox-target\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/09\/skel-06-bromoalkane-rates.svg\" alt=\"Displayed 1-bromobutane, 2-bromobutane and 2-bromo-2-methylpropane with a table of times for the silver bromide precipitate to form\" width=\"1507\" height=\"1224\">\n<\/a>\n<\/div>\n<div class=\"ols-zoom-card-caption\"><p>Part 2 at 50 \u00b0C: 1-bromobutane, 2-bromobutane and 2-bromo-2-methylpropane with their times and 1\/t values, and why the tertiary compound is fastest.<\/p><\/div>\n<\/div>\n<div class=\"ols-key-box\">\n<p><strong>Evaluation point:<\/strong> A time of 3 s is too short to measure reliably: reaction time alone is about \u00b10.2 s at the start and at the stop.<\/p><p>To improve Part 2, run it at a lower temperature (room temperature is enough for the tertiary compound) or use more dilute reagents so that every time is at least 30 s.<\/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>Check: Why the Tertiary Compound Is Fastest<\/h2>\n<p>A student explains the tertiary result with a bond enthalpy argument; pick the statement that would earn the marks.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-1013\" class=\"h5p-iframe\" data-content-id=\"1013\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Rates of Hydrolysis MCQ: Why the Tertiary Compound Is Fastest\"><\/iframe><\/div><\/div>\n<\/section>\n<article class=\"ols-note-card soft\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">10<\/div>\n<h2>Exam-Style Data Interpretation<\/h2>\n<\/div>\n<p>A common exam version gives times for equal moles (equal amounts of substance) of 2-chloropropane, 2-bromopropane and 2-iodopropane in the same total volume at 50 \u00b0C, together with electronegativities and bond enthalpies, and asks you to explain the trend.<\/p><p>Equal moles in the same total volume gives the same concentration of each halogenoalkane, so concentration cannot be the cause of any difference.<\/p>\n<div class=\"ols-table-wrap\">\n<table class=\"ols-table\">\n<thead>\n<tr><th>Halogenoalkane<\/th><th>Time to first cloudiness \/ s<\/th><th>1\/t \/ s\u207b\u00b9 (2 s.f.)<\/th><th>Electronegativity of the halogen<\/th><th>Mean C\u2013X bond enthalpy \/ kJ mol\u207b\u00b9<\/th><\/tr>\n<\/thead>\n<tbody>\n<tr><td><strong>2-iodopropane<\/strong><\/td><td>31<\/td><td>0.032<\/td><td>2.7<\/td><td>228<\/td><\/tr>\n<tr><td><strong>2-bromopropane<\/strong><\/td><td>74<\/td><td>0.014<\/td><td>3.0<\/td><td>290<\/td><\/tr>\n<tr><td><strong>2-chloropropane<\/strong><\/td><td>241<\/td><td>0.0041<\/td><td>3.2<\/td><td>346<\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<p><strong>Why not electronegativity?<\/strong> Chlorine is the most electronegative, so the C\u2013Cl carbon is the most \u03b4+ and should attract the nucleophile most strongly. If that controlled the rate, 2-chloropropane would be fastest. It is slowest, so the polarity argument fails.<\/p>\n<p><strong>Why does bond enthalpy explain the trend?<\/strong> The C\u2013X bond is broken in the rate-determining step. A stronger bond needs more energy to break, so the activation energy is higher and a smaller fraction of collisions succeed.<\/p><p>C\u2013Cl (346 kJ mol\u207b\u00b9) is the strongest and 2-chloropropane is slowest; C\u2013I (228 kJ mol\u207b\u00b9) is the weakest and 2-iodopropane is fastest.<\/p>\n<p><strong>Working with 1\/t.<\/strong> 1\/31 = 0.032 s\u207b\u00b9, 1\/74 = 0.014 s\u207b\u00b9, 1\/241 = 0.0041 s\u207b\u00b9. The iodo compound reacts about 0.032 \/ 0.0041 \u2248 8 times faster than the chloro compound. Quote 1\/t to 2 significant figures, because the times themselves are only known to the nearest second.<\/p>\n<div class=\"ols-key-box\">\n<p><strong>Exam wording:<\/strong> &#8220;Equal moles in the same volume gives equal concentrations, so the difference in rate is due to the halogenoalkane. The C\u2013I bond has the lowest bond enthalpy, so it breaks most easily and 2-iodopropane hydrolyses fastest, even though iodine is the least electronegative halogen.&#8221;<\/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>Check: Describe and Explain<\/h2>\n<p>Write a six-mark answer describing how you would compare three pentyl compounds and explaining the expected order; the key terms are marked automatically.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-1014\" class=\"h5p-iframe\" data-content-id=\"1014\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Rates of Hydrolysis Explain: Compare Three Compounds\"><\/iframe><\/div><\/div>\n<\/section>\n<article class=\"ols-note-card\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">11<\/div>\n<h2>Errors, Uncertainty and Improvements<\/h2>\n<\/div>\n<p>The stop clock reads to 0.01 s, but the real uncertainty is your <strong>reaction time<\/strong> (about \u00b10.2 s at the start and again at the stop, so \u00b10.4 s in total) and, far larger, the judgement of &#8220;first cloudiness&#8221;, which can differ by \u00b12 s between observers. Percentage uncertainty = (uncertainty \/ reading) \u00d7 100.<\/p>\n<p>Reaction time on 606 s: (0.4 \/ 606) \u00d7 100 = 0.066 %. Reaction time on 52 s: (0.4 \/ 52) \u00d7 100 = 0.77 %. Reaction time on 3 s: (0.4 \/ 3) \u00d7 100 = 13 %. Judgement of the endpoint (\u00b12 s) on 3 s: (2 \/ 3) \u00d7 100 = 67 %. Thermometer (\u00b10.5 \u00b0C) on 50 \u00b0C: (0.5 \/ 50) \u00d7 100 = 1.0 %. Graduated pipette (\u00b10.05 cm\u00b3) on 1 cm\u00b3 of silver nitrate: (0.05 \/ 1) \u00d7 100 = 5.0 %. The short Part 2 times, not the apparatus, dominate the uncertainty.<\/p>\n<div class=\"ols-table-wrap\">\n<table class=\"ols-table\">\n<thead>\n<tr><th>Source of error<\/th><th>Effect on the result<\/th><th>Improvement<\/th><\/tr>\n<\/thead>\n<tbody>\n<tr><td><strong>Tube lifted out of the bath to inspect it<\/strong><\/td><td>Mixture cools, time too long, comparison unfair<\/td><td>Keep the tube in the bath; view it against a white tile behind the beaker<\/td><\/tr>\n<tr><td><strong>Silver nitrate not warmed<\/strong><\/td><td>Mixture below 50 \u00b0C at the start, all times too long<\/td><td>Stand the silver nitrate tube in the same bath for the same time<\/td><\/tr>\n<tr><td><strong>Different volumes of silver nitrate<\/strong><\/td><td>Different Ag\u207a and water concentrations, times not comparable<\/td><td>Use a graduated pipette to add exactly 1 cm\u00b3 to every tube<\/td><\/tr>\n<tr><td><strong>Drops not equal moles<\/strong><\/td><td>Different amounts of each halogenoalkane; concentration not truly controlled<\/td><td>Measure equal moles by mass or with a graduated pipette<\/td><\/tr>\n<tr><td><strong>Endpoint judged differently for each tube<\/strong><\/td><td>Random error of several seconds, worst for short times<\/td><td>Same observer, same white background, repeat and average; or use a light sensor and data logger<\/td><\/tr>\n<tr><td><strong>Clock started late (after shaking)<\/strong><\/td><td>All times too short; fastest compound most affected<\/td><td>Start the clock as the silver nitrate is added, then shake once<\/td><\/tr>\n<tr><td><strong>Tertiary time of 3 s too short to measure<\/strong><\/td><td>Percentage uncertainty above 50 %<\/td><td>Lower the bath temperature or dilute the reagents so every time exceeds 30 s<\/td><\/tr>\n<tr><td><strong>Bath temperature drifts during a long run<\/strong><\/td><td>Later tubes at a different temperature<\/td><td>Monitor with a thermometer and top up with hot water; use a thermostatically controlled bath<\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<div class=\"ols-key-box\">\n<p><strong>Key idea:<\/strong> The apparatus errors are small (1 % to 5 %); the endpoint judgement and reaction time on very short times are large. An improvement that lengthens the times, or replaces the eye with a sensor, does more than a better pipette.<\/p>\n<\/div>\n<\/article>\n<article class=\"ols-note-card soft\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">12<\/div>\n<h2>Confirming the Precipitate with Ammonia<\/h2>\n<\/div>\n<p>Because white AgCl and cream AgBr look alike in a cloudy tube, the halide test is completed with <strong>ammonia solution<\/strong>.<\/p><p>Silver chloride dissolves in dilute NH\u2083(aq) to give the colourless complex ion [Ag(NH\u2083)\u2082]\u207a; silver bromide dissolves only in concentrated NH\u2083(aq); silver iodide dissolves in neither.<\/p><p>Nitric acid is added before the silver nitrate in the general test to remove carbonate and hydroxide ions, but in the hydrolysis experiment it is not needed because the only anion released is the halide.<\/p>\n<div class=\"ols-table-wrap\">\n<table class=\"ols-table\">\n<thead>\n<tr><th>Precipitate<\/th><th>Colour<\/th><th>Dilute NH\u2083(aq)<\/th><th>Concentrated NH\u2083(aq)<\/th><\/tr>\n<\/thead>\n<tbody>\n<tr><td><strong>AgCl(s)<\/strong><\/td><td>White<\/td><td>Dissolves: AgCl(s) + 2NH\u2083(aq) \u2192 [Ag(NH\u2083)\u2082]\u207a(aq) + Cl\u207b(aq)<\/td><td>Dissolves<\/td><\/tr>\n<tr><td><strong>AgBr(s)<\/strong><\/td><td>Cream<\/td><td>Insoluble<\/td><td>Dissolves: AgBr(s) + 2NH\u2083(aq) \u2192 [Ag(NH\u2083)\u2082]\u207a(aq) + Br\u207b(aq)<\/td><\/tr>\n<tr><td><strong>AgI(s)<\/strong><\/td><td>Yellow<\/td><td>Insoluble<\/td><td>Insoluble<\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<p>The solubility trend follows the solubility of the silver halides themselves: AgCl is the least insoluble and AgI the most, so only AgCl can be pulled into solution by dilute ammonia. Link this to <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/required-practicals\/rp4-rp6-identifying-inorganic-ions-and-organic-functional-groups\/\">Required Practicals 4 and 6 (analysis of inorganic and organic unknowns)<\/a>, where the same test identifies unknown halides.<\/p>\n<div class=\"ols-key-box\">\n<p><strong>Exam wording:<\/strong> &#8220;Add dilute ammonia solution: the white precipitate dissolves, so it was silver chloride. A cream precipitate that dissolves only in concentrated ammonia is silver bromide.&#8221;<\/p>\n<\/div>\n<\/article>\n<article class=\"ols-note-card\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">13<\/div>\n<h2>Common Mistakes<\/h2>\n<\/div>\n<ul>\n<li><strong>&#8220;Silver nitrate causes the hydrolysis.&#8221;<\/strong> Water hydrolyses the halogenoalkane; silver ions only detect the halide ion released.<\/li>\n<li><strong>&#8220;Ethanol is the nucleophile.&#8221;<\/strong> Ethanol is the solvent. The nucleophile is water from the aqueous silver nitrate.<\/li>\n<li><strong>&#8220;A yellow precipitate shows iodine is present.&#8221;<\/strong> Yellow AgI shows iodide ions, released by hydrolysis of an iodo compound.<\/li>\n<li><strong>&#8220;Chlorine is most electronegative, so the chloro compound is fastest.&#8221;<\/strong> The data show the opposite: bond enthalpy controls the rate, and C\u2013Cl is the strongest bond.<\/li>\n<li><strong>&#8220;The tertiary compound is fastest because its C\u2013Br bond is weaker.&#8221;<\/strong> The bond is the same; the tertiary carbocation is more stable.<\/li>\n<li><strong>Taking the tube out of the bath to look at it.<\/strong> The temperature drops and the comparison is no longer fair; hold the tube in the bath against a white background.<\/li>\n<li><strong>Comparing a Part 1 time with a Part 2 time.<\/strong> They are separate runs; compare only within a run.<\/li>\n<li><strong>Quoting a rate in mol dm\u207b\u00b3 s\u207b\u00b9.<\/strong> The experiment gives relative rates from 1\/t, nothing more.<\/li>\n<\/ul>\n<\/article>\n<section class=\"ols-h5p-card ols-h5p-inline\">\n<span class=\"ols-h5p-kicker\">Check your understanding<\/span>\n<h2>Check: Rates of Hydrolysis Summary<\/h2>\n<p>Six rounds; in each pick the one accurate statement about reagents, endpoint, 1\/t, bond enthalpy, carbocations and precipitate colours.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-1015\" class=\"h5p-iframe\" data-content-id=\"1015\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Rates of Hydrolysis Summary: Rates of Hydrolysis\"><\/iframe><\/div><\/div>\n<\/section>\n<article class=\"ols-note-card\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">14<\/div>\n<h2>Common Exam Points<\/h2>\n<\/div>\n<h3>Say<\/h3><p>&#8220;Water from the aqueous silver nitrate is the nucleophile; ethanol is the solvent.&#8221;<\/p><p>&#8220;Relative rate is proportional to 1\/t, so the shortest time is the fastest.&#8221;<\/p><p>&#8220;The C\u2013I bond has the lowest mean bond enthalpy (228 kJ mol\u207b\u00b9), so it breaks most easily in the rate-determining step.&#8221;<\/p><p>&#8220;The tertiary carbocation is stabilised by three alkyl groups, so the C\u2013Br bond breaks first and the tertiary halogenoalkane hydrolyses fastest.&#8221;<\/p>\n<h3>Do not say<\/h3><p>&#8220;Silver nitrate hydrolyses the halogenoalkane.&#8221; &#8220;Ethanol is the nucleophile.&#8221; &#8220;The chloro compound is fastest because C\u2013Cl is the most polar bond.&#8221; &#8220;The yellow precipitate is iodine.&#8221; &#8220;The rate was 52 s.&#8221;<\/p>\n<h3>Watch for<\/h3><p>Every equation needs state symbols: Ag\u207a(aq) + Br\u207b(aq) \u2192 AgBr(s). Give 1\/t to 2 significant figures with the unit s\u207b\u00b9. In an evaluation, name the variable that was not controlled and say which way the time moves (too long or too short), then give the improvement.<\/p>\n<\/article>\n<section class=\"ols-faq-card\">\n<h2>FAQs<\/h2>\n<p>Quick answers to the questions students ask most about Practical Skills: Rates of Hydrolysis and the hydrolysis of halogenoalkanes.<\/p>\n\n<div class=\"ols-faq-list\">\n<div class=\"ols-faq-item\">\n<h3>How is the rate measured in this practical?<\/h3>\n<p>It is not measured directly. The time from adding the aqueous silver nitrate to the first cloudiness is recorded, and relative rate is taken as 1\/t. A shorter time means a faster hydrolysis, and the 1\/t values can be compared within one run at one temperature.<\/p>\n<\/div>\n\n<div class=\"ols-faq-item\">\n<h3>Why does no precipitate form before the silver nitrate is added?<\/h3>\n<p>Because there is no water in the tube. Ethanol and the halogenoalkane do not react; the water that acts as the nucleophile arrives with the aqueous silver nitrate, so hydrolysis and the release of halide ions start at that moment.<\/p>\n<\/div>\n\n<div class=\"ols-faq-item\">\n<h3>Why does 1-iodobutane react faster than 1-chlorobutane?<\/h3>\n<p>The C\u2013I bond has a lower mean bond enthalpy (228 kJ mol\u207b\u00b9) than C\u2013Cl (346 kJ mol\u207b\u00b9), so it breaks more easily in the rate-determining step and the activation energy is lower. Electronegativity would predict the opposite order, so it is not the controlling factor.<\/p>\n<\/div>\n\n<div class=\"ols-faq-item\">\n<h3>Why is 2-bromo-2-methylpropane so much faster than 1-bromobutane?<\/h3>\n<p>Both have a C\u2013Br bond, so bond enthalpy cannot explain it.<\/p><p>The tertiary compound loses its bromide first to form the carbocation (CH\u2083)\u2083C\u207a, stabilised by the positive inductive effect of three alkyl groups. That stable carbocation forms readily, so the reaction is fast.<\/p><p>This is the S\u20991 route; primary compounds react by the S\u20992 route in which water attacks the \u03b4+ carbon directly.<\/p>\n<\/div>\n\n<div class=\"ols-faq-item\">\n<h3>Why is it hard to tell silver chloride from silver bromide?<\/h3>\n<p>White and cream look alike in a cloudy tube. Add ammonia solution: dilute ammonia dissolves silver chloride, concentrated ammonia dissolves silver bromide and silver iodide dissolves in neither.<\/p>\n<\/div>\n\n<div class=\"ols-faq-item\">\n<h3>Why must there be no naked flames?<\/h3>\n<p>Ethanol and the halogenoalkanes are highly flammable and volatile, so the water bath is filled from a kettle and never heated with a Bunsen burner. Bung the tubes while they warm so that the vapour is not lost.<\/p>\n<\/div>\n<\/div>\n<\/section>\n<section class=\"ols-related-card\">\n<h2>Related Required Practicals Pages<\/h2>\n<p>Use these pages to connect the practical techniques with each other and with the rest of the course.<\/p>\n<div class=\"ols-related-grid\">\n<a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/required-practicals\/molar-volume-of-a-gas\/\">Gas volumes: Molar Volume of a Gas<\/a>\n<a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/required-practicals\/rp2-measurement-of-an-enthalpy-change\/\">RP2: Enthalpy Change via Hess&#8217;s Law<\/a>\n<a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/required-practicals\/rp1-acid-base-titration\/\">RP1: Concentration of HCl by Titration<\/a>\n<a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/required-practicals\/rp1-making-a-volumetric-solution\/\">RP1: Preparation of a Standard Solution<\/a>\n<a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/required-practicals\/preparing-an-organic-liquid-chlorination-of-2-methylpropan-2-ol\/\">Organic prep: Chlorination of 2-methylpropan-2-ol<\/a>\n<a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/required-practicals\/rp5-distillation-of-a-product-oxidation-of-ethanol\/\">RP5: Oxidation of an Alcohol<\/a>\n<a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/required-practicals\/rp4-rp6-identifying-inorganic-ions-and-organic-functional-groups\/\">RP4 and RP6: Analysis of Inorganic and Organic Unknowns<\/a>\n<a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/required-practicals\/\">Required Practicals Overview<\/a>\n<\/div>\n<\/section>\n<section class=\"ols-attribution-card\">\n        <p><strong>Copyright and author footprint:<\/strong> This OLS revision page was written for Online Learning System by <strong>Dr. Mohammed Al-Fatah<\/strong>. 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