{"id":11566,"date":"2026-09-28T14:13:05","date_gmt":"2026-09-28T13:13:05","guid":{"rendered":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/practical-skills\/gravimetric-analysis-water-of-crystallisation\/"},"modified":"2026-10-03T08:38:13","modified_gmt":"2026-10-03T07:38:13","slug":"gravimetric-analysis-water-of-crystallisation","status":"publish","type":"page","link":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/practical-skills\/gravimetric-analysis-water-of-crystallisation\/","title":{"rendered":"Gravimetric Analysis: Water of Crystallisation and Composition of a Solid"},"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; }\n    .ols-main { min-width: 0; max-width: 970px; }\n    .ols-breadcrumbs { display: flex; flex-wrap: wrap; gap: 8px; margin: 10px 0 22px; font-size: 15px; color: var(--grey-text); }\n    .ols-breadcrumbs a, .ols-breadcrumbs span { color: var(--grey-text); text-decoration: none; font-weight: 600; }\n    .ols-breadcrumbs a:hover { color: var(--blue); text-decoration: underline; text-underline-offset: 3px; }\n    .ols-title-card, .ols-note-card, .ols-h5p-card, .ols-related-card, .ols-faq-card { background: #ffffff; border: 1px solid var(--border); border-radius: 28px; box-shadow: var(--shadow); padding: 34px; margin-bottom: 24px; overflow: hidden; }\n    .ols-title-card { background: linear-gradient(135deg, #ffffff 0%, #f8fbff 100%); }\n    .ols-title-card h1 { margin: 0 0 18px; font-size: clamp(36px, 5vw, 58px); line-height: 1.08; font-weight: 800; letter-spacing: -0.04em; color: #111827; }\n    .ols-page-intro { font-size: 19px; line-height: 1.7; font-weight: 300; color: var(--body-text); margin: 0 0 22px; }\n    .ols-badges { display: flex; flex-direction: column; align-items: flex-start; gap: 12px; margin-bottom: 22px; }\n    .ols-badge { display: inline-flex; align-items: center; padding: 9px 14px; border-radius: 999px; background: #ffffff; border: 1px solid var(--border); font-size: 15px; font-weight: 600; color: var(--navy); }\n    .ols-author { display: flex; align-items: center; gap: 20px; padding: 28px; border-radius: 28px; background: linear-gradient(135deg, #ffffff 0%, #f8fbff 100%); border: 1px solid rgba(28,36,75,0.12); box-shadow: 0 18px 45px rgba(28,36,75,0.10); margin-top: 22px; }\n    .ols-author-avatar-img { width: 92px; height: 92px; border-radius: 50%; object-fit: cover; object-position: center; flex-shrink: 0; border: 4px solid #ffffff; box-shadow: 0 14px 32px rgba(28,36,75,0.18), 0 0 0 1px rgba(28,36,75,0.10); transition: transform 0.25s ease, box-shadow 0.25s ease; }\n    .ols-author:hover .ols-author-avatar-img { transform: scale(1.04); box-shadow: 0 20px 42px rgba(28,36,75,0.22), 0 0 0 1px rgba(28,36,75,0.10); }\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; font-size: 20px; line-height: 1.3; color: var(--navy); }\n    .ols-faq-item p { margin: 0; font-size: 16px; line-height: 1.65; color: var(--body-text); }\n\n    .ols-related-grid { display: grid; grid-template-columns: repeat(3, minmax(0, 1fr)); gap: 16px; margin-top: 18px; }\n    .ols-related-item { border: 1px solid var(--border); border-radius: 18px; padding: 18px; background: #ffffff; color: var(--navy); text-decoration: none; font-weight: 600; line-height: 1.5; transition: transform 0.2s ease, box-shadow 0.2s ease; }\n    .ols-related-item:hover { transform: translateY(-2px); box-shadow: 0 10px 22px rgba(28, 36, 75, 0.08); }\n\n    .ols-course-cta-covalent {\n      width: 100%;\n      margin: 30px 0 24px;\n      font-family: Poppins, Arial, sans-serif;\n    }\n    .ols-course-cta-covalent, .ols-course-cta-covalent * { box-sizing: border-box; }\n    .ols-course-cta-card {\n      overflow: hidden;\n      border-radius: 30px;\n      border: 1px solid var(--border);\n      background: radial-gradient(circle at top left, rgba(37, 99, 235, 0.16), transparent 34%), linear-gradient(135deg, #ffffff 0%, #f8fbff 100%);\n      box-shadow: var(--shadow);\n      padding: 30px;\n    }\n    .ols-course-cta-top {\n      display: grid;\n      grid-template-columns: minmax(260px, 0.9fr) minmax(0, 1.1fr);\n      gap: 28px;\n      align-items: center;\n      margin-bottom: 24px;\n    }\n    .ols-course-cta-image-link { display: block; 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>Cambridge International AS Level Chemistry<\/p>\n  <\/div>\n\n  <div class=\"ols-topic-group\">\n    <h4>Practical Skills (Paper 3)<\/h4>\n\n    <ul class=\"ols-topic-list\">\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/practical-skills\/molar-volume-of-a-gas\/\">Gas collection: Molar Volume of a Gas<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/practical-skills\/enthalpy-change-via-hess-law\/\">Thermometry: Enthalpy Change via Hess's Law<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/practical-skills\/concentration-of-hcl-by-titration\/\">Titration: Concentration of HCl by Titration<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/practical-skills\/preparation-of-a-standard-solution\/\">Standard solution: Preparation of a Standard Solution<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/practical-skills\/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\/cie\/practical-skills\/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\/cie\/practical-skills\/oxidation-of-an-alcohol-distillation-and-reflux\/\">Distil or reflux: Oxidation of an Alcohol<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/practical-skills\/qualitative-analysis-of-inorganic-and-organic-unknowns\/\">Qualitative analysis: Analysis of Inorganic and Organic Unknowns<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/practical-skills\/rates-of-reaction-timing-an-observation\/\">Rates: Rates of Reaction<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/practical-skills\/gravimetric-analysis-water-of-crystallisation\/\">Gravimetric: Gravimetric and Composition Analysis<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/practical-skills\/redox-titrations-manganate-vii-and-iodine-thiosulfate\/\">Redox titrations: Redox Titrations<\/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\/cie\/\">Cambridge International (CIE) Chemistry<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/practical-skills\/\">Practical Skills (Paper 3)<\/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\/cie\/\">Cambridge International (CIE)<\/a> \/\n<a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/practical-skills\/\">Practical Skills (Paper 3)<\/a> \/\n<span>Gravimetric Analysis: Water of Crystallisation and Composition of a Solid<\/span>\n<\/nav>\n\n      <header class=\"ols-title-card\">\n        <h1>Gravimetric Analysis: Water of Crystallisation and Composition of a Solid<\/h1>\n        <p class=\"ols-page-intro\">A focused revision guide to gravimetric analysis for Cambridge International A Level Chemistry: heating a hydrated salt to constant mass to find its water of crystallisation, the percentage decomposition of a carbonate, the composition of copper(II) carbonate, composition from a gas volume, and the errors and uncertainties that decide the answer.<\/p>\n\n        <div class=\"ols-badges\">\n<div class=\"ols-badge\">AS Level<\/div>\n<div class=\"ols-badge\">Practical Skills: Gravimetric Analysis<\/div>\n<div class=\"ols-badge\">9701 Paper 3<\/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 Cambridge International AS and 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: Mass, Moles and Hydrated Salts<\/h2>\n<p>Three quick questions on the GCSE ideas this practical builds on: relative formula mass, conservation of mass in an open crucible, and dehydrating copper(II) sulfate.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-content\" data-content-id=\"1049\"><\/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>This practical, Practical Skills: Gravimetric Analysis on the Cambridge International course, uses <strong>changes in mass<\/strong> to find a formula or a composition.<\/p><p>A weighed solid is heated in a crucible until nothing more is lost, the residue is weighed, and the masses are turned into moles.<\/p><p>The main example is the number of moles of <strong>water of crystallisation<\/strong>, x, in hydrated copper(II) sulfate, CuSO\u2084\u00b7xH\u2082O. The same method finds how much of a carbonate has decomposed and which of two possible formulae a compound has.<\/p>\n<p class=\"ols-equation\">CuSO\u2084\u00b7xH\u2082O(s) \u2192 CuSO\u2084(s) + xH\u2082O(g)<\/p>\n<p>The practical paper expects you to be able to <strong>heat a solid in a crucible on a pipe-clay triangle<\/strong> and record any mass change.<\/p>\n<p>The example given is the determination of the water of hydration of a hydrated salt from the change in mass.<\/p>\n<p>The syllabus also lists gas-volume experiments that find the composition of a solid from the volume of carbon dioxide given off, and the terms anhydrous, hydrated and water of crystallisation (2.3.4) with the mole calculations that go with them (2.4.1).<\/p>\n<p>On the Cambridge International course this practical is examined through Paper 3, a timed laboratory examination that assesses manipulation, observation, presentation of data, analysis and evaluation.<\/p><p>Questions ask you to explain heating to constant mass and cooling in a desiccator, to calculate x or a percentage from the masses, to predict the direction of each error, and to work out a percentage uncertainty from the balance resolution.<\/p><p>Weighing by difference is the same skill as in <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/practical-skills\/preparation-of-a-standard-solution\/\">Practical Skills: Standard Solutions (preparation of a standard solution)<\/a>.<\/p>\n<div class=\"ols-key-box\">\n<p><strong>Definition:<\/strong> Water of crystallisation is water that is chemically bonded within the crystal lattice of a hydrated salt, in a fixed ratio shown in the formula, for example CuSO\u2084\u00b75H\u2082O. Anhydrous means without water of crystallisation.<\/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 apparatus decides both how completely the solid can be heated and how precisely the masses are known.<\/p>\n<div class=\"ols-table-wrap\">\n<table class=\"ols-table\">\n<thead>\n<tr><th>Item<\/th><th>What it is for<\/th><th>Precision or note<\/th><\/tr>\n<\/thead>\n<tbody>\n<tr><td><strong>Porcelain crucible and lid<\/strong><\/td><td>Holds the solid while it is heated strongly; the lid is placed slightly ajar<\/td><td>withstands a Bunsen flame; weighed with its lid every time<\/td><\/tr>\n<tr><td><strong>Pipe-clay triangle on a tripod<\/strong><\/td><td>Supports the crucible directly in the flame<\/td><td>clay-covered wire does not react with or stick to the crucible<\/td><\/tr>\n<tr><td><strong>Bunsen burner and heat-resistant mat<\/strong><\/td><td>Heats gently at first, then more strongly<\/td><td>too strong a flame decomposes some anhydrous salts<\/td><\/tr>\n<tr><td><strong>Crucible tongs<\/strong><\/td><td>Moves the hot crucible<\/td><td>never touch the crucible by hand<\/td><\/tr>\n<tr><td><strong>Desiccator<\/strong><\/td><td>The crucible cools in a dry atmosphere<\/td><td>stops the anhydrous salt absorbing water from the air<\/td><\/tr>\n<tr><td><strong>Balance<\/strong><\/td><td>Weighs the crucible empty, with the hydrated salt, and after each heating<\/td><td>2 d.p. balance: \u00b10.005 g per reading, \u00b10.01 g for a mass found by difference<\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<div class=\"ols-key-box\">\n<p><strong>Safety:<\/strong> Wear eye protection: hydrated salts can spit when first heated. Copper(II) sulfate is harmful if swallowed and an irritant.<\/p><p>A crucible stays hot long after it stops glowing, so use tongs and place it on the mat or in the desiccator, never on the bench. Do not look directly down into a crucible that is being heated.<\/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>Method: Step by Step<\/h2>\n<\/div>\n<p>The method below is for hydrated copper(II) sulfate, chosen because the colour change from blue to white shows the progress of the heating. Every mass is recorded to 0.01 g.<\/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>Weigh the crucible<\/strong><\/td><td>Weigh a clean, dry crucible and lid.<\/td><td>Every other mass is found by difference from this one.<\/td><\/tr>\n<tr><td><strong>Add the salt<\/strong><\/td><td>Add about 2.5 g of hydrated copper(II) sulfate and weigh the crucible, lid and contents.<\/td><td>A mass of this size gives a mass loss large enough to measure precisely on a 2 d.p. balance.<\/td><\/tr>\n<tr><td><strong>Heat gently<\/strong><\/td><td>Heat the crucible on a pipe-clay triangle with the lid slightly ajar, gently at first and then more strongly.<\/td><td>Gentle heating stops the solid spitting out; the gap lets the water vapour escape.<\/td><\/tr>\n<tr><td><strong>Do not overheat<\/strong><\/td><td>Keep the flame below red heat once the solid has turned white.<\/td><td>Anhydrous CuSO\u2084 decomposes to black copper(II) oxide if heated too strongly, which would add to the mass loss.<\/td><\/tr>\n<tr><td><strong>Cool<\/strong><\/td><td>Move the crucible with tongs into a desiccator and let it cool.<\/td><td>Anhydrous copper(II) sulfate absorbs water from the air as it cools; a hot crucible also gives a false reading.<\/td><\/tr>\n<tr><td><strong>Weigh<\/strong><\/td><td>Weigh the cool crucible, lid and residue.<\/td><td>This is the first value of the mass after heating.<\/td><\/tr>\n<tr><td><strong>Constant mass<\/strong><\/td><td>Repeat heating, cooling and weighing until two consecutive masses agree within 0.01 g.<\/td><td>No further change shows that all the water of crystallisation has been removed.<\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<!-- 3D card: gravimetric (27 Sep 2026) -->\n<!-- Copyright (c) 2026 Dr. Mohammed Al-Fatah, onlinelearningsystem.net. 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width:100%; height:100%; margin:0; border-radius:0; border:0; padding:16px 20px; display:flex; flex-direction:column; overflow:auto;}\n.ols-grv-001:fullscreen .grv-head{display:none;}\n.ols-grv-001:fullscreen .grv-stage{flex:1 1 auto; height:auto; min-height:320px;}\n.ols-grv-001:-webkit-full-screen{max-width:none; width:100%; height:100%; margin:0; border-radius:0; border:0; padding:16px 20px; display:flex; flex-direction:column; overflow:auto;}\n.ols-grv-001:-webkit-full-screen .grv-head{display:none;}\n.ols-grv-001:-webkit-full-screen .grv-stage{flex:1 1 auto; height:auto; min-height:320px;}\n\n.ols-cc-grv-001{\n  font-family:'Poppins',system-ui,-apple-system,'Segoe UI',Roboto,Helvetica,Arial,sans-serif;\n  margin:10px auto 0; text-align:center; font-size:11px; font-style:italic; color:#aab0c0;\n}\n.ols-cc-grv-001 a{color:#aab0c0; text-decoration:none;}\n.ols-cc-grv-001 a:hover{text-decoration:underline;}\n<\/style>\n\n<div class=\"grv-head\">\n  <h2 class=\"grv-title\">Gravimetric Analysis: Heating to Constant Mass<\/h2>\n  <p class=\"grv-sub\">Weigh a hydrated salt, heat it to constant mass and find its formula, then use the same crucible to measure a carbonate decomposing and to decide the formula of a green copper compound.<\/p>\n<\/div>\n\n<div class=\"grv-stage\" id=\"grvStage\" tabindex=\"0\" aria-label=\"Film of the practical. Space plays or pauses, the left and right arrow keys skip 10 seconds.\">\n  <canvas class=\"grv-canvas\" id=\"grvCanvas\" aria-hidden=\"true\"><\/canvas>\n  <div class=\"grv-overlay\" id=\"grvOverlay\"><\/div>\n  <div class=\"grv-subt\" id=\"grvSubt\"><\/div>\n  <div class=\"grv-hint\" id=\"grvHint\" hidden>Paused: drag to look around<\/div>\n  <button type=\"button\" class=\"grv-poster\" id=\"grvPoster\" aria-label=\"Play the film\"><svg viewBox=\"0 0 24 24\" aria-hidden=\"true\"><path d=\"M7 4.5v15l12.5-7.5z\"\/><\/svg><span>Replay<\/span><\/button>\n<\/div>\n\n<div class=\"grv-player\" id=\"grvPlayer\" role=\"group\" aria-label=\"Film controls\">\n  <button type=\"button\" class=\"grv-pb\" id=\"grvPlay\" aria-label=\"Play\"><svg viewBox=\"0 0 24 24\" aria-hidden=\"true\"><path d=\"M7 4.5v15l12.5-7.5z\"\/><\/svg><\/button>\n  <button type=\"button\" class=\"grv-pb\" id=\"grvBack\" aria-label=\"Back 10 seconds\"><svg viewBox=\"0 0 24 24\" aria-hidden=\"true\"><path d=\"M12 4V1.5L7.5 5 12 8.5V6a7 7 0 1 1-7 7H3a9 9 0 1 0 9-9z\"\/><text x=\"12.2\" y=\"16.2\" text-anchor=\"middle\">10<\/text><\/svg><\/button>\n  <button type=\"button\" class=\"grv-pb\" id=\"grvFwd\" aria-label=\"Forward 10 seconds\"><svg viewBox=\"0 0 24 24\" aria-hidden=\"true\"><path d=\"M12 4V1.5L16.5 5 12 8.5V6a7 7 0 1 0 7 7h2a9 9 0 1 1-9-9z\"\/><text x=\"11.8\" y=\"16.2\" text-anchor=\"middle\">10<\/text><\/svg><\/button>\n  <button type=\"button\" class=\"grv-pb\" id=\"grvRestart\" aria-label=\"Restart\"><svg viewBox=\"0 0 24 24\" aria-hidden=\"true\"><path d=\"M5.5 5h2.2v14H5.5zM9.2 12l9.3 6.8V5.2z\"\/><\/svg><\/button>\n  <div class=\"grv-prog\" id=\"grvProg\" role=\"slider\" tabindex=\"0\" aria-label=\"Seek\" aria-valuemin=\"0\" aria-valuemax=\"260\" aria-valuenow=\"0\" aria-valuetext=\"0:00\">\n    <div class=\"grv-track\"><div class=\"grv-fill\" id=\"grvFill\"><\/div><\/div>\n    <div class=\"grv-thumb\" id=\"grvThumb\"><\/div>\n  <\/div>\n  <span class=\"grv-time\" id=\"grvTime\">0:00 \/ 4:20<\/span>\n  <button type=\"button\" class=\"grv-pb grv-speed\" id=\"grvSpeed\" aria-label=\"Playback speed 1\u00d7\">1\u00d7<\/button>\n  <button type=\"button\" class=\"grv-pb\" id=\"grvFs\" aria-label=\"Full screen\"><svg viewBox=\"0 0 24 24\" aria-hidden=\"true\"><path d=\"M4 9V4h5v2H6v3zm11-5h5v5h-2V6h-3zM4 15h2v3h3v2H4zm14 3v-3h2v5h-5v-2z\"\/><\/svg><\/button>\n<\/div>\n<div class=\"grv-chips\" id=\"grvChips\" role=\"group\" aria-label=\"Chapters\"><\/div>\n<\/section>\n\n<p class=\"ols-cc-grv-001\">&copy; Dr. Mohammed Al-Fatah &#8211; <a href=\"https:\/\/www.onlinelearningsystem.net\" target=\"_blank\" rel=\"noopener\">onlinelearningsystem.net<\/a><\/p>\n<script src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/JS\/gravimetric.js?v=20260928c\"><\/script>\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\/core-practical-grav-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-grav-apparatus.jpg\" alt=\"Crucible with its lid ajar on a pipe-clay triangle over a Bunsen burner, with tongs, a desiccator and a balance reading to 0.01 g\">\n<\/a>\n<\/div>\n<div class=\"ols-zoom-card-caption\"><p>The apparatus for heating a hydrated salt to constant mass: crucible and lid on a pipe-clay triangle, a desiccator for cooling and a balance reading to 0.01 g.<\/p><\/div>\n<\/div>\n<div class=\"ols-key-box\">\n<p><strong>Technique point:<\/strong> Always weigh the crucible with its lid, and use the same balance for every weighing, so that any zero error cancels when the masses are subtracted.<\/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: Heating a New Salt to Constant Mass<\/h2>\n<p>Order the method for a different hydrated salt.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-1050\" class=\"h5p-iframe\" data-content-id=\"1050\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Gravimetric Analysis Practical Order: Heating a New Salt to Constant Mass\"><\/iframe><\/div><\/div>\n<\/section>\n<article class=\"ols-note-card soft\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">4<\/div>\n<h2>Results and Calculating x<\/h2>\n<\/div>\n<p>The table gives a complete set of results. The mass fell sharply after the first heating and then by only 0.07 g and 0.01 g, so the last two weighings show that constant mass was reached.<\/p>\n<div class=\"ols-table-wrap\">\n<table class=\"ols-table\">\n<thead>\n<tr><th>Measurement<\/th><th>Mass \/ g<\/th><\/tr>\n<\/thead>\n<tbody>\n<tr><td><strong>Crucible and lid<\/strong><\/td><td>22.35<\/td><\/tr>\n<tr><td><strong>Crucible, lid and hydrated CuSO\u2084<\/strong><\/td><td>24.85<\/td><\/tr>\n<tr><td><strong>After heating 1<\/strong><\/td><td>24.03<\/td><\/tr>\n<tr><td><strong>After heating 2<\/strong><\/td><td>23.96<\/td><\/tr>\n<tr><td><strong>After heating 3<\/strong><\/td><td>23.95<\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\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-grav-constmass.jpg?v=2\" 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-grav-constmass.jpg?v=2\" alt=\"Heating hydrated copper(II) sulfate to constant mass: blue crystals turn white and the last two weighings agree within 0.01 g\">\n<\/a>\n<\/div>\n<div class=\"ols-zoom-card-caption\"><p>Heating hydrated copper(II) sulfate to constant mass: the blue crystals turn white and the last two weighings agree within 0.01 g.<\/p><\/div>\n<\/div>\n<p><strong>Worked Example.<\/strong> Mr of CuSO\u2084 = 63.5 + 32.1 + (4 \u00d7 16.0) = 159.6; Mr of H\u2082O = 18.0.<\/p>\n<p class=\"ols-equation\">Step 1: mass of anhydrous CuSO\u2084 = 23.95 \u2212 22.35 = 1.60 g<\/p>\n<p class=\"ols-equation\">Step 2: mass of water lost = 24.85 \u2212 23.95 = 0.90 g<\/p>\n<p class=\"ols-equation\">Step 3: moles of CuSO\u2084 = 1.60 \u00f7 159.6 = 0.0100 mol; moles of H\u2082O = 0.90 \u00f7 18.0 = 0.0500 mol<\/p>\n<p class=\"ols-equation\">Step 4: x = 0.0500 \u00f7 0.0100 = 4.99, which rounds to 5<\/p>\n<p><strong>Answer:<\/strong> the formula is CuSO\u2084\u00b75H\u2082O. The same data give the Mr of the hydrated salt directly.<\/p><p>Mr = 2.50 g \u00f7 0.0100 mol = 249, and (249 \u2212 159.6) \u00f7 18.0 = 5.0 water molecules per formula unit.<\/p><p>Round x to the nearest whole number only at the end, and say why: a value of 4.99 comes from experimental error, not from a fraction of a water molecule.<\/p>\n<div class=\"ols-key-box\">\n<p><strong>Exam wording:<\/strong> &#8220;Heat to constant mass: heat, cool in a desiccator and weigh, repeating until two consecutive masses agree within 0.01 g, to make sure all the water has been removed.&#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: Finding x for Hydrated Zinc Sulfate<\/h2>\n<p>Work through the calculation for a different hydrated salt.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-content\" data-content-id=\"1051\"><\/div><\/div>\n<\/section>\n<article class=\"ols-note-card\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">5<\/div>\n<h2>Thermal Decomposition of a Group 2 Carbonate<\/h2>\n<\/div>\n<p>The same crucible method measures how far a <strong>thermal decomposition<\/strong> has gone. A Group 2 carbonate loses carbon dioxide on heating, so the mass lost is the mass of CO\u2082, and the moles of CO\u2082 equal the moles of carbonate decomposed.<\/p>\n<p class=\"ols-equation\">CaCO\u2083(s) \u2192 CaO(s) + CO\u2082(g)<\/p>\n<p><strong>Worked Example.<\/strong> 2.00 g of calcium carbonate (Mr 100.1) is heated strongly in a crucible without a lid for several periods, and the mass of solid falls to 1.34 g.<\/p>\n<p class=\"ols-equation\">Step 1: moles of CaCO\u2083 at the start = 2.00 \u00f7 100.1 = 0.0200 mol<\/p>\n<p class=\"ols-equation\">Step 2: mass of CO\u2082 lost = 2.00 \u2212 1.34 = 0.66 g; moles of CO\u2082 = 0.66 \u00f7 44.0 = 0.0150 mol<\/p>\n<p class=\"ols-equation\">Step 3: percentage converted to CaO = 0.0150 \u00f7 0.0200 \u00d7 100 = 75.1%<\/p>\n<p><strong>Answer:<\/strong> 75.1% of the calcium carbonate was converted to calcium oxide. Complete decomposition would have left 0.0200 \u00d7 56.1 = 1.12 g of CaO.<\/p><p>Calcium carbonate needs a temperature of about 900 \u00b0C, close to the limit of a Bunsen flame, so incomplete decomposition is expected.<\/p><p>Magnesium carbonate decomposes at a much lower temperature because the smaller Mg\u00b2\u207a ion polarises the carbonate ion more.<\/p><p>A simple check on the residue is to add dilute acid: effervescence shows that some carbonate is left.<\/p>\n<div class=\"ols-key-box\">\n<p><strong>Remember:<\/strong> The mass lost is the gas. Convert it to moles of CO\u2082 and use the 1 : 1 ratio with the carbonate, not the mass of the residue alone.<\/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: Percentage Decomposition of Magnesium Carbonate<\/h2>\n<p>Apply the same calculation to a different Group 2 carbonate.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-1052\" class=\"h5p-iframe\" data-content-id=\"1052\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Gravimetric Analysis Practical Fill In: Percentage Decomposition of Magnesium Carbonate\"><\/iframe><\/div><\/div>\n<\/section>\n<article class=\"ols-note-card soft\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">6<\/div>\n<h2>Composition of Copper(II) Carbonate<\/h2>\n<\/div>\n<p>The compound sold as &#8220;copper(II) carbonate&#8221; is green, and heating it to constant mass shows what it really is. It turns black as <strong>copper(II) oxide<\/strong> forms. Two formulae are possible, and each predicts a different mass of residue from the same starting mass.<\/p>\n<p class=\"ols-equation\">CuCO\u2083(s) \u2192 CuO(s) + CO\u2082(g)<\/p>\n<p class=\"ols-equation\">CuCO\u2083\u00b7Cu(OH)\u2082(s) \u2192 2CuO(s) + CO\u2082(g) + H\u2082O(g)<\/p>\n<div class=\"ols-table-wrap\">\n<table class=\"ols-table\">\n<thead>\n<tr><th>Possible formula<\/th><th>Mr<\/th><th>Residue from 2.00 g<\/th><th>Residue as % of the start<\/th><\/tr>\n<\/thead>\n<tbody>\n<tr><td><strong>CuCO\u2083<\/strong><\/td><td>123.5<\/td><td>2.00 \u00d7 79.5 \u00f7 123.5 = 1.29 g<\/td><td>64.4%<\/td><\/tr>\n<tr><td><strong>CuCO\u2083\u00b7Cu(OH)\u2082<\/strong><\/td><td>221.0<\/td><td>2.00 \u00d7 (2 \u00d7 79.5) \u00f7 221.0 = 1.44 g<\/td><td>71.9%<\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<p>A student heats 2.00 g of the green solid to constant mass and obtains <strong>1.44 g<\/strong> of black residue, 72.0% of the starting mass.<\/p><p>This matches the second formula, so the solid is basic copper(II) carbonate, CuCO\u2083\u00b7Cu(OH)\u2082, and not CuCO\u2083.<\/p><p>Measuring the carbon dioxide given off would decide the formula just as well.<\/p>\n<div class=\"ols-key-box\">\n<p><strong>Key idea:<\/strong> To choose between formulae, predict the result (residue mass, mass lost or gas volume) for each one and see which the experiment matches.<\/p>\n<\/div>\n<\/article>\n<article class=\"ols-note-card\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">7<\/div>\n<h2>Composition From a Gas Volume<\/h2>\n<\/div>\n<p>A carbonate in a mixture can also be measured by the <strong>volume of carbon dioxide<\/strong> it gives with excess acid, collected over water or in a gas syringe.<\/p><p>The volume gives the moles of CO\u2082, the equation gives the moles of carbonate, and the moles give its mass and its percentage in the sample.<\/p><p>Only the carbonate reacts to give gas, so any unreactive impurity makes the percentage less than 100%.<\/p>\n<p>This is the gas-volume experiment named in the practical paper.<\/p><p>The worked example, the percentage of calcium carbonate in an impure sample from 96.0 cm\u00b3 of CO\u2082, together with the method and its errors, is on <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/practical-skills\/molar-volume-of-a-gas\/\">Practical Skills: Gas Collection (molar volume of a gas)<\/a>; it is not repeated here.<\/p><p>The gas method is quicker than heating to constant mass and suits carbonates that decompose only at high temperature, but carbon dioxide dissolving in the water makes the volume, and so the percentage, slightly too low.<\/p>\n<div class=\"ols-key-box\">\n<p><strong>Remember:<\/strong> Mass method: mass lost = mass of CO\u2082. Gas method: volume \u00f7 24.0 dm\u00b3 mol\u207b\u00b9 (at room temperature and pressure) = moles of CO\u2082. Both lead to moles of carbonate by the equation.<\/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: Which Compound Is It?<\/h2>\n<p>Use a residue mass to decide between two possible formulae for a new compound.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-content\" data-content-id=\"1053\"><\/div><\/div>\n<\/section>\n<article class=\"ols-note-card soft\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">8<\/div>\n<h2>Errors, Uncertainty and Improvements<\/h2>\n<\/div>\n<p>Every error in this practical changes one of two masses, the water (or gas) lost or the residue, and so pushes the answer one way. Name the error, give its direction and give an improvement that removes it.<\/p>\n<div class=\"ols-table-wrap\">\n<table class=\"ols-table\">\n<thead>\n<tr><th>Source of error<\/th><th>Effect on x (or on the % decomposed)<\/th><th>Improvement<\/th><\/tr>\n<\/thead>\n<tbody>\n<tr><td><strong>Incomplete dehydration or decomposition<\/strong><\/td><td>Too little lost: x (or the %) too low<\/td><td>Heat to constant mass: repeat until two masses agree within 0.01 g<\/td><\/tr>\n<tr><td><strong>Decomposition beyond the anhydrous salt (overheating)<\/strong><\/td><td>Extra gas lost: x too high<\/td><td>Heat gently once the solid is white; keep below red heat<\/td><\/tr>\n<tr><td><strong>Solid spitting out of the crucible<\/strong><\/td><td>Extra mass lost: x too high<\/td><td>Heat gently at first with the lid ajar<\/td><\/tr>\n<tr><td><strong>Anhydrous salt absorbing water while cooling<\/strong><\/td><td>Residue too heavy: x too low<\/td><td>Cool in a desiccator and weigh as soon as it is cool<\/td><\/tr>\n<tr><td><strong>Weighing while still warm<\/strong><\/td><td>Convection currents give a falsely low reading, so the loss looks too large<\/td><td>Let the crucible reach room temperature in the desiccator<\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\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-grav-errors.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-grav-errors.jpg\" alt=\"Four error cards showing whether each error makes the calculated x too high or too low\">\n<\/a>\n<\/div>\n<div class=\"ols-zoom-card-caption\"><p>The direction of each error when finding the water of crystallisation: incomplete heating and water absorbed on cooling make x too low; overheating and spitting make it too high.<\/p><\/div>\n<\/div>\n<p><strong>Percentage uncertainties.<\/strong> A 2 d.p. balance has an uncertainty of \u00b10.005 g per reading, and each mass in this practical is the difference of two readings, so it carries \u00b10.01 g.<\/p><p>For the water lost, 0.01 \u00f7 0.90 \u00d7 100 = 1.1%; for the anhydrous salt, 0.01 \u00f7 1.60 \u00d7 100 = 0.63%.<\/p><p>A larger sample, or a 3 d.p. balance, reduces both; halving the sample to 1.25 g would double the percentage uncertainty in the water lost to about 2.2%.<\/p>\n<div class=\"ols-key-box\">\n<p><strong>Exam focus:<\/strong> Do not write &#8220;heat it for longer&#8221;. Write &#8220;heat to constant mass&#8221;, and say what it shows: that all the water (or carbon dioxide) has been removed.<\/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: Errors in Heating Experiments<\/h2>\n<p>Choose the correct statements about the errors in heating experiments.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-1054\" class=\"h5p-iframe\" data-content-id=\"1054\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Gravimetric Analysis Practical Summary: Errors in Heating Experiments\"><\/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>Common Mistakes<\/h2>\n<\/div>\n<p>The same errors appear in students&#8217; write-ups and exam answers year after year. Each one costs a mark that the corrected version earns.<\/p>\n<ul>\n<li>Dividing the mass of water by the mass of salt instead of dividing the <strong>moles<\/strong> of water by the moles of anhydrous salt.<\/li>\n<li>Using the Mr of the hydrated salt to find the moles of anhydrous salt.<\/li>\n<li>Rounding x from 4.6 to 5 without comment. A value that far from a whole number means an error in the experiment, and it should be said.<\/li>\n<li>Writing &#8220;heat for longer&#8221; instead of &#8220;heat to constant mass&#8221;.<\/li>\n<li>Forgetting the desiccator, or weighing the crucible while it is still warm.<\/li>\n<li>Getting the direction of an error wrong: overheating and spitting make x too high; incomplete heating and water absorbed on cooling make it too low.<\/li>\n<li>Quoting the uncertainty of one balance reading (\u00b10.005 g) for a mass found by difference (\u00b10.01 g).<\/li>\n<\/ul>\n<\/article>\n<article class=\"ols-note-card\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">10<\/div>\n<h2>Common Exam Points<\/h2>\n<\/div>\n<h3>Say<\/h3><p>&#8220;Heat to constant mass, cooling in a desiccator before each weighing, until two consecutive masses agree within 0.01 g.&#8221; &#8220;x = moles of water lost \u00f7 moles of anhydrous salt.&#8221; &#8220;The mass lost is the mass of carbon dioxide, so moles of CO\u2082 = moles of carbonate decomposed.&#8221;<\/p>\n<h3>Do not say<\/h3><p>&#8220;Heat until it looks white.&#8221; (The colour is not proof that all the water has gone.) &#8220;The error is human error.&#8221; &#8220;x = 4.6, so the formula is CuSO\u2084\u00b74.6H\u2082O.&#8221;<\/p>\n<h3>Watch for<\/h3><p>Data where the mass has not reached constant mass; questions that give a percentage composition instead of masses; a choice between two formulae from a residue mass; percentage uncertainty for a mass found by difference; the gas-volume route to the composition of a solid.<\/p>\n<\/article>\n<section class=\"ols-faq-card\">\n<h2>FAQs<\/h2>\n<p>Short answers to the questions students most often ask about gravimetric analysis.<\/p>\n\n<div class=\"ols-faq-list\">\n<div class=\"ols-faq-item\">\n<h3>Why do we heat to constant mass rather than for a fixed time?<\/h3>\n<p>Because a fixed time may not remove all the water or carbon dioxide. When two consecutive weighings agree within the resolution of the balance, nothing more is being lost, so the dehydration or decomposition is complete.<\/p>\n<\/div>\n\n<div class=\"ols-faq-item\">\n<h3>Why is the crucible cooled in a desiccator?<\/h3>\n<p>An anhydrous salt absorbs water from the air as it cools, which would make the final mass too high and x too low. A hot crucible also sets up air currents that make the balance read too low. The desiccator lets it cool in dry air.<\/p>\n<\/div>\n\n<div class=\"ols-faq-item\">\n<h3>Why is the lid left slightly ajar?<\/h3>\n<p>With the lid fully on, water vapour cannot escape; with it off, the solid can spit out when it is first heated. A small gap lets the vapour out and keeps the solid in.<\/p>\n<\/div>\n\n<div class=\"ols-faq-item\">\n<h3>What if my value of x is not a whole number?<\/h3>\n<p>Round it to the nearest whole number for the formula, but comment on it. A value such as 4.6 points to an error, most often incomplete heating (too low) or spitting and overheating (too high).<\/p>\n<\/div>\n\n<div class=\"ols-faq-item\">\n<h3>How do I find which formula a compound has?<\/h3>\n<p>Work out what each possible formula predicts, for example the mass of residue from the mass you heated, then compare with your result. The formula whose prediction matches is the one supported by the experiment.<\/p>\n<\/div>\n<\/div>\n<\/section>\n<section class=\"ols-related-card\">\n<h2>Related Practical Skills 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\/cie\/practical-skills\/molar-volume-of-a-gas\/\">Gas collection: Molar Volume of a Gas<\/a>\n<a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/practical-skills\/enthalpy-change-via-hess-law\/\">Thermometry: 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\/cie\/practical-skills\/concentration-of-hcl-by-titration\/\">Titration: Concentration of HCl by Titration<\/a>\n<a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/practical-skills\/preparation-of-a-standard-solution\/\">Standard solution: Preparation of a Standard Solution<\/a>\n<a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/practical-skills\/rates-of-hydrolysis-of-halogenoalkanes\/\">Hydrolysis rates: Hydrolysis of Halogenoalkanes<\/a>\n<a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/practical-skills\/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\/cie\/practical-skills\/oxidation-of-an-alcohol-distillation-and-reflux\/\">Distil or reflux: Oxidation of an Alcohol<\/a>\n<a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/practical-skills\/qualitative-analysis-of-inorganic-and-organic-unknowns\/\">Qualitative analysis: Analysis of Inorganic and Organic Unknowns<\/a>\n<a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/practical-skills\/rates-of-reaction-timing-an-observation\/\">Rates: Rates of Reaction<\/a>\n<a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/practical-skills\/redox-titrations-manganate-vii-and-iodine-thiosulfate\/\">Redox titrations: Redox Titrations<\/a>\n<a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/practical-skills\/\">Practical Skills (Paper 3) 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>. It is designed for A Level Chemistry revision and should not be copied or redistributed without permission.<\/p>\n      <\/section>\n\n      <div class=\"ols-image-lightbox\" id=\"olsImageLightboxNatureCovalentBonding9ch0\" aria-hidden=\"true\" role=\"dialog\" aria-modal=\"true\" aria-label=\"Expanded revision image\">\n        <div class=\"ols-image-lightbox-inner\">\n          <button class=\"ols-image-lightbox-close\" type=\"button\" aria-label=\"Close enlarged image\">\u00d7<\/button>\n          <img decoding=\"async\" class=\"ols-image-lightbox-img\" src=\"\" alt=\"\">\n        <\/div>\n      <\/div>\n\n      <script>\n        (function(){\n          var page = document.querySelector(\".ols-nature-of-covalent-bonding-9ch0-page\");\n          if (!page) { return; }\n          var lightbox = page.querySelector(\"#olsImageLightboxNatureCovalentBonding9ch0\");\n          if (!lightbox) { return; }\n          var lightboxImage = lightbox.querySelector(\".ols-image-lightbox-img\");\n    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