{"id":11274,"date":"2026-09-27T14:51:31","date_gmt":"2026-09-27T13:51:31","guid":{"rendered":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/required-practicals\/rp1-acid-base-titration\/"},"modified":"2026-10-03T08:38:11","modified_gmt":"2026-10-03T07:38:11","slug":"rp1-acid-base-titration","status":"publish","type":"page","link":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/required-practicals\/rp1-acid-base-titration\/","title":{"rendered":"Required Practical 1: Acid\u2013Base Titration"},"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>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>Required Practical 1: Acid\u2013Base Titration<\/span>\n<\/nav>\n\n      <header class=\"ols-title-card\">\n        <h1>Required Practical 1: Acid\u2013Base Titration<\/h1>\n        <p class=\"ols-page-intro\">Required Practical 1 finds the concentration of a hydrochloric acid solution by diluting it tenfold and titrating 25.0 cm\u00b3 aliquots against standardised 0.0800 mol dm\u207b\u00b3 sodium hydroxide with phenolphthalein. This page gives the method with the reason for every step, corrected sample results, the full calculation to 0.963 mol dm\u207b\u00b3, the error directions and the percentage uncertainty budget that Papers 1, 2 and 3 questions demand.<\/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\">Required Practical 1<\/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: Neutralisation and Volumes<\/h2>\n<p>Three quick questions on what you already know: the apparatus that measures a fixed 25.0 cm\u00b3, the products of neutralisation and how a burette volume is worked out.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-content\" data-content-id=\"992\"><\/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 Required Practical 1 you find the <strong>concentration<\/strong> of a hydrochloric acid solution that is too concentrated to titrate directly.<\/p><p>You pipette 25.0 cm\u00b3 of the original acid into a 250 cm\u00b3 volumetric flask and make it up to the mark with distilled water.<\/p><p>You then titrate 25.0 cm\u00b3 portions (aliquots) of the diluted acid against a <strong>standardised<\/strong> sodium hydroxide solution of concentration 0.0800 mol dm\u207b\u00b3 using phenolphthalein.<\/p><p>The mean titre gives the moles of alkali, the equation gives the moles of acid, and a scale-up of ten takes you back to the original solution.<\/p>\n<p>The reaction is a strong acid neutralising a strong base:<\/p>\n<p>HCl(aq) + NaOH(aq) \u2192 NaCl(aq) + H\u2082O(l)<\/p>\n<p>The <strong>ionic equation<\/strong>, which is asked for at least as often, is H\u207a(aq) + OH\u207b(aq) \u2192 H\u2082O(l). The ratio is 1 : 1, so at the end point the moles of NaOH delivered from the burette equal the moles of HCl in the flask.<\/p>\n<p>The sodium hydroxide has to be <strong>standardised<\/strong> first because it cannot be a primary standard: solid NaOH absorbs water and carbon dioxide from the air, so a solution made by weighing it never has the concentration you calculate.<\/p>\n<p>Its concentration is found by titrating it against a primary standard such as anhydrous sodium carbonate (see <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/required-practicals\/rp1-making-a-volumetric-solution\/\">Required Practical 1 (preparation of a standard solution)<\/a>).<\/p>\n<div class=\"ols-key-box\"><p><strong>Common mistake:<\/strong> Students lose marks by writing &#8220;the NaOH is a standard solution&#8221; as if weighing it out were enough.<\/p><\/div>\n\n<p>Required Practical 1 on AQA is usually run the other way round: you first make a standard solution from a weighed solid, most often anhydrous sodium carbonate (see <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/required-practicals\/rp1-making-a-volumetric-solution\/\">Required Practical 1 (preparation of a standard solution)<\/a>).<\/p><p>You then titrate the acid against it, with methyl orange as the usual indicator.<\/p><p>Every technique below (pipette, burette, end point, concordant titres, uncertainty) is examined in exactly the same way, and the calculation from a mass is worked through further down this page.<\/p>\n\n\n<p>You are assessed through the written papers (at least 15% of the marks test practical skills) and the practical endorsement.<\/p><p>For this practical that means: the reasons for each technique step, the direction of the error each mistake causes, the treatment of the results table, the calculation with correct units and significant figures, and the percentage uncertainty budget.<\/p>\n<div class=\"ols-key-box\">\n<p><strong>Key idea:<\/strong> The whole practical is stoichiometry on top of accurate volumes: moles of alkali from c \u00d7 V, moles of acid from the equation, then scale from the aliquot to the flask and back to the original acid.<\/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: Equations and Mole Ratios<\/h2>\n<p>Write state symbols and the ionic equation for a different acid and alkali, and use the mole ratio.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-993\" class=\"h5p-iframe\" data-content-id=\"993\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Titration of Hydrochloric Acid Fill In: State Symbols and Mole Ratio\"><\/iframe><\/div><\/div>\n<\/section>\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>An apparatus question wants the full list with a reason for each item, and the precision of the measuring glassware. The items students forget are the small ones: the white tile, the funnel, the wash bottle, the dropping pipette and the stopper.<\/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>25 cm\u00b3 volumetric pipette and filler<\/strong><\/td><td>Measures 25.0 cm\u00b3 of the original acid into the volumetric flask, then 25.0 cm\u00b3 aliquots of the diluted acid into the conical flask<\/td><td>\u00b10.06 cm\u00b3; never mouth-pipette<\/td><\/tr>\n<tr><td><strong>250 cm\u00b3 volumetric flask with stopper<\/strong><\/td><td>Dilutes the 25.0 cm\u00b3 sample to exactly 250 cm\u00b3; stoppered and inverted to mix<\/td><td>\u00b10.3 cm\u00b3; one graduation line only<\/td><\/tr>\n<tr><td><strong>50 cm\u00b3 burette, clamp and stand<\/strong><\/td><td>Delivers a measured, variable volume of NaOH(aq) into the flask<\/td><td>\u00b10.05 cm\u00b3 per reading, read to the nearest 0.05 cm\u00b3<\/td><\/tr>\n<tr><td><strong>Small funnel<\/strong><\/td><td>Fills the burette without spills; removed before the initial reading<\/td><td>Left in, it drips and lowers the reading<\/td><\/tr>\n<tr><td><strong>250 cm\u00b3 conical flask<\/strong><\/td><td>Holds the aliquot during titration; its shape lets you swirl without loss<\/td><td>Rinsed with distilled water only<\/td><\/tr>\n<tr><td><strong>White tile<\/strong><\/td><td>Sits under the flask so the faint pink end point is seen against white<\/td><td>A sheet of white paper also works<\/td><\/tr>\n<tr><td><strong>Wash bottle of distilled water and dropping pipette<\/strong><\/td><td>Makes the volumetric flask up to the mark, the last drops one at a time; rinses the pipette tip into the flask<\/td><td>Overshooting the mark means starting again<\/td><\/tr>\n<tr><td><strong>Beakers<\/strong><\/td><td>Hold the original acid, the diluted acid and the NaOH(aq) while pipetting and filling<\/td><td>Label them<\/td><\/tr>\n<tr><td><strong>Reagents<\/strong><\/td><td>Hydrochloric acid, about 1 mol dm\u207b\u00b3; sodium hydroxide, 0.0800 mol dm\u207b\u00b3, standardised; phenolphthalein indicator<\/td><td>Quote the alkali concentration with its status: standardised<\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<div class=\"ols-key-box\">\n<p><strong>Hazards and precautions:<\/strong> Hydrochloric acid at about 1 mol dm\u207b\u00b3 is low hazard; sodium hydroxide at 0.0800 mol dm\u207b\u00b3 is an irritant; phenolphthalein is dissolved in ethanol, which is flammable.<\/p><p>Wear eye protection throughout, wipe up spills at once and wash any splash off the skin with plenty of water. Use a pipette filler, never the mouth.<\/p><p>Fill the burette below eye level, standing it on the bench or a low stool, so that alkali cannot splash into the eyes.<\/p><p>That last point is the safety mark examiners give; &#8220;take care with glassware&#8221; earns nothing.<\/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: What Each Precaution Does<\/h2>\n<p>Decide whether each step in a titration reduces random error, reduces systematic error or is there for safety only.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-994\" class=\"h5p-iframe\" data-content-id=\"994\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Titration of Hydrochloric Acid Quick Choice: Random, Systematic or Safety\"><\/iframe><\/div><\/div>\n<\/section>\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>Every step carries a reason. Method questions in Papers 1, 2 and 3 are marked on the reasons and the numbers, not on the bare instruction, so learn the third column as carefully as the second.<\/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<\/strong><\/td><td>Rinse the 25 cm\u00b3 pipette with a little of the hydrochloric acid and discard the rinsings<\/td><td>Water left inside would dilute the acid drawn up, so fewer moles would be transferred<\/td><\/tr>\n<tr><td><strong>2<\/strong><\/td><td>Pipette 25.0 cm\u00b3 of the hydrochloric acid into a rinsed 250 cm\u00b3 volumetric flask, touching the tip against the inside of the neck; do not blow out the last drop<\/td><td>The pipette is calibrated to leave that drop behind; blowing it out transfers extra acid<\/td><\/tr>\n<tr><td><strong>3<\/strong><\/td><td>Rinse the pipette tip and the neck of the flask into the bulb with distilled water<\/td><td>Every drop of acid must end up in the 250 cm\u00b3<\/td><\/tr>\n<tr><td><strong>4<\/strong><\/td><td>Add distilled water to about 1 cm below the line, then add the last drops with a dropping pipette until the bottom of the meniscus sits on the line, read at eye level<\/td><td>Overshooting cannot be undone: the flask is emptied and the dilution repeated<\/td><\/tr>\n<tr><td><strong>5<\/strong><\/td><td>Stopper and invert the flask at least ten times<\/td><td>Without mixing the aliquots taken later would have different concentrations (a random error)<\/td><\/tr>\n<tr><td><strong>6<\/strong><\/td><td>Rinse the burette with distilled water, then with the NaOH(aq); fill through a funnel, open the tap to fill the jet, then remove the funnel and take the initial reading to the nearest 0.05 cm\u00b3<\/td><td>Water in the burette dilutes the alkali; an air bubble in the jet and drips from the funnel both give false readings; the initial reading need not be 0.00<\/td><\/tr>\n<tr><td><strong>7<\/strong><\/td><td>Rinse the conical flask with distilled water only, pipette in 25.0 cm\u00b3 of the diluted acid (rinsing the pipette with diluted acid first) and add 2 to 3 drops of phenolphthalein<\/td><td>Water in the conical flask does not change the moles of acid in it, but rinsing it with acid would add extra moles and enlarge the titre<\/td><\/tr>\n<tr><td><strong>8<\/strong><\/td><td>Stand the flask on a white tile and run in NaOH(aq) from the burette, swirling continuously, until the first permanent pink appears; record the final reading. This is the rough titre<\/td><td>The rough titre locates the end point roughly so that the accurate titrations can be run dropwise near it; it is never used in the mean<\/td><\/tr>\n<tr><td><strong>9<\/strong><\/td><td>Repeat with fresh aliquots, adding the alkali quickly to within about 2 cm\u00b3 of the rough titre and then drop by drop, swirling, until the first faint pink persists for about 30 s<\/td><td>One drop is about 0.05 cm\u00b3, so dropwise addition is what makes the end point sharp<\/td><\/tr>\n<tr><td><strong>10<\/strong><\/td><td>Continue until at least two titres agree within 0.10 cm\u00b3 of each other; record every reading to two decimal places ending in 0 or 5<\/td><td>Concordant titres show the random error is small; the mean of those titres alone goes into the calculation<\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<div class=\"ols-key-box\">\n<p><strong>Exam wording:<\/strong> &#8220;Rinse the pipette with the acid, the burette with the alkali and the conical flask with distilled water.&#8221; One sentence, three rinses, three different reasons; students who write &#8220;rinse all the glassware with water&#8221; lose the mark.<\/p>\n<\/div>\n<\/article>\n<!-- 3D card: titration-hcl-naoh (27 Sep 2026) -->\n<!-- Copyright (c) 2026 Dr. Mohammed Al-Fatah, onlinelearningsystem.net. 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padding:5px 10px; border-radius:10px; bottom:10px;}\n.ols-tit-001 .tit-narrow .tit-poster{width:74px; height:74px; margin:-37px 0 0 -37px;}\n.ols-tit-001 .tit-narrow .tit-poster svg{width:32px; height:32px;}\n\n@media (max-width:760px){\n  .ols-tit-001{padding:26px; border-radius:22px;}\n  .ols-tit-001 h2.tit-title{font-size:20.5px;}\n  .ols-tit-001 p.tit-sub{font-size:13.5px;}\n  .ols-tit-001 .tit-stage{height:560px;}\n}\n@media (max-width:560px){\n  .ols-tit-001 .tit-player{padding:6px 8px;}\n  .ols-tit-001 .tit-prog{order:-1; flex:1 1 100%; margin:0 4px;}\n  .ols-tit-001 .tit-pb{width:36px; height:36px;}\n  .ols-tit-001 .tit-time{margin-right:auto;}\n  .ols-tit-001 .tit-chip{font-size:11.5px; padding:5px 10px;}\n}\n@media (max-width:480px){\n  .ols-tit-001{padding:14px; border-radius:18px;}\n  .ols-tit-001 .tit-head{margin-bottom:14px;}\n}\n@media (prefers-reduced-motion:reduce){\n  .ols-tit-001 .tit-poster,.ols-tit-001 .tit-chip,.ols-tit-001 .tit-pb{transition:none;}\n}\n\n\/* full screen: the card fills the screen and the stage takes the spare height *\/\n.ols-tit-001:fullscreen{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-tit-001:fullscreen .tit-head{display:none;}\n.ols-tit-001:fullscreen .tit-stage{flex:1 1 auto; height:auto; min-height:320px;}\n.ols-tit-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-tit-001:-webkit-full-screen .tit-head{display:none;}\n.ols-tit-001:-webkit-full-screen .tit-stage{flex:1 1 auto; height:auto; min-height:320px;}\n\n.ols-cc-tit-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-tit-001 a{color:#aab0c0; text-decoration:none;}\n.ols-cc-tit-001 a:hover{text-decoration:underline;}\n<\/style>\n\n<div class=\"tit-head\">\n  <h2 class=\"tit-title\">Titration: HCl against Standardised NaOH<\/h2>\n  <p class=\"tit-sub\">Dilute a sample of hydrochloric acid, titrate 25.0 cm\u00b3 portions against 0.0800 mol dm\u207b\u00b3 sodium hydroxide with phenolphthalein, and work back to the concentration of the original acid.<\/p>\n<\/div>\n\n<div class=\"tit-stage\" id=\"titStage\" tabindex=\"0\" aria-label=\"Film of the practical. Space plays or pauses, the left and right arrow keys skip 10 seconds.\">\n  <canvas class=\"tit-canvas\" id=\"titCanvas\" aria-hidden=\"true\"><\/canvas>\n  <div class=\"tit-overlay\" id=\"titOverlay\"><\/div>\n  <div class=\"tit-subt\" id=\"titSubt\"><\/div>\n  <div class=\"tit-hint\" id=\"titHint\" hidden>Paused: drag to look around<\/div>\n  <button type=\"button\" class=\"tit-poster\" id=\"titPoster\" 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=\"tit-player\" id=\"titPlayer\" role=\"group\" aria-label=\"Film controls\">\n  <button type=\"button\" class=\"tit-pb\" id=\"titPlay\" 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=\"tit-pb\" id=\"titBack\" 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=\"tit-pb\" id=\"titFwd\" 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=\"tit-pb\" id=\"titRestart\" 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=\"tit-prog\" id=\"titProg\" role=\"slider\" tabindex=\"0\" aria-label=\"Seek\" aria-valuemin=\"0\" aria-valuemax=\"210\" aria-valuenow=\"0\" aria-valuetext=\"0:00\">\n    <div class=\"tit-track\"><div class=\"tit-fill\" id=\"titFill\"><\/div><\/div>\n    <div class=\"tit-thumb\" id=\"titThumb\"><\/div>\n  <\/div>\n  <span class=\"tit-time\" id=\"titTime\">0:00 \/ 3:30<\/span>\n  <button type=\"button\" class=\"tit-pb tit-speed\" id=\"titSpeed\" aria-label=\"Playback speed 1\u00d7\">1\u00d7<\/button>\n  <button type=\"button\" class=\"tit-pb\" id=\"titFs\" 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=\"tit-chips\" id=\"titChips\" role=\"group\" aria-label=\"Chapters\"><\/div>\n<\/section>\n\n<p class=\"ols-cc-tit-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\/titration-hcl-naoh.js?v=20260928b\"><\/script>\n\n<article class=\"ols-note-card soft\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">4<\/div>\n<h2>Diluting Before You Titrate<\/h2>\n<\/div>\n<p>The dilution step is not always part of Required Practical 1 as you meet it, but the reasoning is examined in planning questions and the technique is the same one used to make a standard solution.<\/p><p>An acid of about 1 mol dm\u207b\u00b3 contains 0.025 mol of HCl in 25.0 cm\u00b3. Titrating that with 0.0800 mol dm\u207b\u00b3 NaOH would need 0.025 \u00f7 0.0800 = 0.31 dm\u00b3, about 300 cm\u00b3 of alkali, six burette fillings, each adding its own reading uncertainty.<\/p><p>After a tenfold dilution the 25.0 cm\u00b3 aliquot holds 0.0025 mol and needs about 30 cm\u00b3, which fits a 50 cm\u00b3 burette comfortably and keeps the percentage uncertainty in the titre near 0.3%.<\/p>\n<p>The <strong>dilution factor<\/strong> is 250 \u00f7 25.0 = 10. Every mole that was in the 25.0 cm\u00b3 sample is now spread through 250 cm\u00b3, so a 25.0 cm\u00b3 aliquot of the diluted acid contains one tenth of the original moles.<\/p><div class=\"ols-key-box\"><p><strong>Common mistake:<\/strong> That factor of ten reappears in the calculation, and forgetting it is the most common calculation error on this practical.<\/p><\/div>\n<p>Technique decides whether the diluted concentration is what you think it is. The pipette is rinsed with the acid, not water, and is filled until the bottom of the meniscus sits on the line at eye level.<\/p><p>The tip touches the inside of the flask neck as it drains and the last drop stays in the pipette.<\/p><p>Water is added to about 1 cm below the line and then dropwise, because once the meniscus is past the line the only cure is to <strong>discard and repeat<\/strong>: water cannot be taken back out.<\/p><p>Finally the flask is stoppered and inverted at least ten times; a flask that is not inverted gives aliquots of different concentrations and scattered titres.<\/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-titr-dilution.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-titr-dilution.jpg\" alt=\"Five panels: rinse the pipette with the acid, fill to the mark, deliver 25.0 cm\u00b3 into the 250 cm\u00b3 volumetric flask, make up to the mark with a dropping pipette, stopper and invert ten times;\u2026\">\n<\/a>\n<\/div>\n<div class=\"ols-zoom-card-caption\"><p>Diluting the acid: rinse the pipette with the acid, fill to the mark, deliver 25.0 cm\u00b3 into the 250 cm\u00b3 volumetric flask, make up to the line with a dropping pipette, then stopper and invert ten times. Dilution factor = 250 \u00f7 25.0 = 10.<\/p><\/div>\n<\/div>\n<div class=\"ols-key-box\">\n<p><strong>Exam focus:<\/strong> Why dilute? &#8220;So that the titre is about 30 cm\u00b3 and fits the burette; an undiluted titration would need about 300 cm\u00b3 of alkali.&#8221; Why invert? &#8220;So the solution is homogeneous and every aliquot has the same concentration.&#8221; Both are one-mark answers that most students leave blank.<\/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: Dilution Errors<\/h2>\n<p>Apply the dilution reasoning to a different acid and a different flask, and decide which way the error goes.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-995\" class=\"h5p-iframe\" data-content-id=\"995\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Titration of Hydrochloric Acid MCQ: Overfilling the Volumetric Flask\"><\/iframe><\/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>Setting Up the Burette and Running the Titration<\/h2>\n<\/div>\n<p>The burette is rinsed with distilled water and then with the sodium hydroxide solution it will hold.<\/p><p>Filled with a wet burette, the alkali is slightly diluted, a larger volume is needed to supply the same moles of OH\u207b, the titre is <strong>too large<\/strong> and the calculated acid concentration is too high.<\/p><p>The burette is filled through a small funnel, below eye level, and the tap is opened briefly to fill the jet.<\/p><p>An air bubble that sits in the jet at the start and is pushed out during the titration counts as delivered volume that never reached the flask, so again the titre is too large.<\/p><p>Then the <strong>funnel is removed<\/strong> before the initial reading; left in, it drips, the final reading is lower than it should be and the titre is too small.<\/p>\n<p>The initial reading does not have to be 0.00 cm\u00b3. Read the bottom of the meniscus at eye level and record to the nearest 0.05 cm\u00b3, so every reading ends in 0 or 5 in the second decimal place.<\/p>\n<p>Reading from the top of the meniscus every time cancels out in the titre, because the titre is a difference of two readings; reading inconsistently does not cancel and adds random error.<\/p>\n<p>The conical flask is rinsed with distilled water only. Any water left in it makes no difference to the result because all the acid in the flask is titrated whatever its volume.<\/p><p>Rinsing the flask with the diluted acid, by contrast, adds acid that was not measured and enlarges the titre.<\/p><p>A <strong>conical flask<\/strong> rather than a beaker is used because it can be swirled vigorously without splashing out solution.<\/p><p>Two or three drops of phenolphthalein are enough; the indicator is itself a weak acid and consumes a trace of alkali.<\/p>\n<p>During the titration the flask is swirled continuously so that the alkali mixes at once and the pink flashes where it lands disappear.<\/p><p>In the rough titration the alkali is run in steadily to find the approximate end point.<\/p><p>In the accurate titrations it is run in quickly to about 2 cm\u00b3 short of that value and then added <strong>drop by drop<\/strong>, with the flask swirled after each drop, so that the end point is fixed to within one drop, about 0.05 cm\u00b3.<\/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-titr-setup.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-titr-setup.jpg\" alt=\"The whole titration set-up: 50 cm\u00b3 burette of 0.0800 mol dm\u207b\u00b3 NaOH(aq) clamped vertically, funnel removed, 250 cm\u00b3 conical flask of 25.0 cm\u00b3 diluted HCl(aq) with phenolphthalein on a white tile,\u2026\">\n<\/a>\n<\/div>\n<div class=\"ols-zoom-card-caption\"><p>The titration set-up: 50 cm\u00b3 burette of 0.0800 mol dm\u207b\u00b3 NaOH(aq) clamped vertically with the funnel removed, 25.0 cm\u00b3 of diluted HCl(aq) with three drops of phenolphthalein in a 250 cm\u00b3 conical flask on a white tile, and the eye level with the meniscus.<\/p><\/div>\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\/fix-3.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\/fix-3.jpg\" alt=\"Three-panel guide to filling, reading and checking a burette\">\n<\/a>\n<\/div>\n<div class=\"ols-zoom-card-caption\"><p>Using the burette: rinse with the solution, fill with the funnel then remove it, open the tap to fill the jet, and read the bottom of the meniscus at eye level to the nearest 0.05 cm\u00b3 (here 9.15 cm\u00b3).<\/p><p>A funnel left in lowers the final reading; a bubble in the jet inflates the titre.<\/p><\/div>\n<\/div>\n<div class=\"ols-key-box\">\n<p><strong>Exam focus:<\/strong> Three rinsing errors, three directions: pipette rinsed with water, fewer moles of acid, titre too small; burette rinsed with water, dilute alkali, titre too large; conical flask rinsed with acid, extra moles of acid, titre too large. Always finish with the effect on the calculated concentration.<\/p>\n<\/div>\n<\/article>\n<article class=\"ols-note-card soft\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">6<\/div>\n<h2>Spotting the End Point<\/h2>\n<\/div>\n<p>The diluted acid starts colourless because <strong>phenolphthalein<\/strong> is colourless below pH 8.2. As the alkali is added the pH rises slowly, then jumps through many units in a single drop near the equivalence point.<\/p><p>Phenolphthalein changes colour between pH 8.3 and 10, which lies inside the near-vertical section of the strong acid\u2013strong base curve (roughly pH 3.5 to 10.5), so one drop of alkali takes it through its whole colour change and the end point is sharp.<\/p><p>The end point is the <strong>first faint pink<\/strong> that does not disappear on swirling and persists for about 30 s. A strong pink means the end point has been overshot; that titre is <strong>rejected<\/strong>, not corrected.<\/p>\n<p>The <strong>equivalence point<\/strong> is the volume at which the moles of OH\u207b added exactly equal the moles of H\u207a present, pH 7 for a strong acid and strong base.<\/p>\n<p>The <strong>end point<\/strong> is the volume at which the indicator changes colour, pH about 8.3 for phenolphthalein.<\/p>\n<p>With a suitable indicator they differ by a fraction of one drop, which is why the indicator must change colour on the vertical part of the curve.<\/p>\n<p>Methyl orange (red below pH 3.1, yellow above pH 4.4, orange at the end point) is the indicator AQA mark schemes name most often for a strong acid, especially when the alkali is sodium carbonate.<\/p><p>This is because carbonate titrations have their vertical section at low pH where phenolphthalein would change too early.<\/p><p>Universal indicator is never acceptable, because it changes gradually through several colours and gives no sharp end point.<\/p><p>Whichever indicator is used, the colour change is described in the direction of this titration: alkali added to acid, so colourless to pink for phenolphthalein or red to orange for methyl orange.<\/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-titr-indicator.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-titr-indicator.jpg\" alt=\"Three conical flasks with alkali added to acid: colourless before the end point, first faint permanent pink at the end point, deep magenta overshot; phenolphthalein colour strip pH 8.3 to 10\">\n<\/a>\n<\/div>\n<div class=\"ols-zoom-card-caption\"><p>Phenolphthalein with alkali running into acid: colourless before the end point, the first faint permanent pink at the end point (stop and read the burette), and the deep magenta of an overshot titre that must be rejected. The colour strip shows the change over pH 8.3 to 10.<\/p><\/div>\n<\/div>\n<div class=\"ols-key-box\">\n<p><strong>Exam wording:<\/strong> Indicator choice: &#8220;Phenolphthalein changes colour over pH 8.3 to 10, which is within the vertical part of the titration curve, so the end point and the equivalence point coincide to within one drop.&#8221; Name the range, place it on the curve, link it to one drop.<\/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: Choosing an Indicator<\/h2>\n<p>Pick the accurate statement in each round for a weak acid titrated with a strong base.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-996\" class=\"h5p-iframe\" data-content-id=\"996\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Titration of Hydrochloric Acid Summary: Choosing an Indicator\"><\/iframe><\/div><\/div>\n<\/section>\n<article class=\"ols-note-card\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">7<\/div>\n<h2>Recording Titres and Choosing Concordant Results<\/h2>\n<\/div>\n<p>Results are set out with the initial reading before the final reading, every value to two decimal places, and the titre as final minus initial.<\/p><p>The first row is the <strong>rough titre<\/strong>, usually the largest because it is deliberately run past the end point; it is labelled as rough and never enters the mean.<\/p><p><strong>Concordant<\/strong> titres are within 0.10 cm\u00b3 of each other. Below is a corrected set of sample data.<\/p>\n<div class=\"ols-table-wrap\">\n<table class=\"ols-table\">\n<thead>\n<tr><th>Titration<\/th><th>Initial burette reading \/ cm\u00b3<\/th><th>Final burette reading \/ cm\u00b3<\/th><th>Titre \/ cm\u00b3<\/th><th>Used?<\/th><\/tr>\n<\/thead>\n<tbody>\n<tr><td><strong>Rough<\/strong><\/td><td>0.00<\/td><td>30.60<\/td><td>30.60<\/td><td>No: rough titre<\/td><\/tr>\n<tr><td><strong>1<\/strong><\/td><td>0.45<\/td><td>30.55<\/td><td>30.10<\/td><td>Yes: concordant<\/td><\/tr>\n<tr><td><strong>2<\/strong><\/td><td>2.15<\/td><td>32.45<\/td><td>30.30<\/td><td>No: rejected<\/td><\/tr>\n<tr><td><strong>3<\/strong><\/td><td>0.60<\/td><td>30.65<\/td><td>30.05<\/td><td>Yes: concordant<\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<p>Titrations 1 and 3 differ by 0.05 cm\u00b3, so they are concordant. Titration 2 is 0.25 cm\u00b3 away from titration 3 and is rejected even though its readings were taken carefully.<\/p><p>Something, perhaps a pink flash mistaken for the end point or a slow drop after the tap was closed, made it drift.<\/p><p>Mean titre = (30.10 + 30.05) \u00f7 2 = 30.075 cm\u00b3, written as <strong>30.08 cm\u00b3<\/strong> to two decimal places. If you carry the working on a calculator keep 30.075 and round only the final answer.<\/p>\n<p>Students lose marks in three ways here: averaging every titre including the rough one, quoting the mean to three decimal places as if the burette could read it, and writing burette readings such as 30.1 or 30.12 that a burette graduated in 0.1 cm\u00b3 cannot give. Write 30.10 and 30.05.<\/p>\n\n\n<div class=\"ols-key-box\">\n<p><strong>Key idea:<\/strong> Rough titre to locate the end point; accurate titres added dropwise; mean of the concordant titres only (within 0.10 cm\u00b3 of each other); two decimal places ending in 0 or 5.<\/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: Building a Results Table<\/h2>\n<p>Work out the titres from new burette readings, sort them into rough, concordant and rejected, and find the mean.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-997\" class=\"h5p-iframe\" data-content-id=\"997\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Titration of Hydrochloric Acid Drag: Rough, Concordant, Reject and Mean\"><\/iframe><\/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>Worked Calculation from the Mean Titre<\/h2>\n<\/div>\n<p>Data: mean titre 30.08 cm\u00b3 of 0.0800 mol dm\u207b\u00b3 NaOH(aq); 25.0 cm\u00b3 aliquots of acid that had been diluted from 25.0 cm\u00b3 to 250 cm\u00b3. Every line carries its unit.<\/p>\n<div class=\"ols-table-wrap\">\n<table class=\"ols-table\">\n<thead>\n<tr><th>Step<\/th><th>Working<\/th><th>Result<\/th><\/tr>\n<\/thead>\n<tbody>\n<tr><td><strong>1. Titre in dm\u00b3<\/strong><\/td><td>30.08 cm\u00b3 \u00f7 1000<\/td><td>0.03008 dm\u00b3<\/td><\/tr>\n<tr><td><strong>2. Moles of NaOH<\/strong><\/td><td>n = c \u00d7 V = 0.0800 mol dm\u207b\u00b3 \u00d7 0.03008 dm\u00b3<\/td><td>0.0024064 mol<\/td><\/tr>\n<tr><td><strong>3. Moles of HCl in the aliquot<\/strong><\/td><td>1 : 1 ratio from HCl(aq) + NaOH(aq) \u2192 NaCl(aq) + H\u2082O(l)<\/td><td>0.0024064 mol<\/td><\/tr>\n<tr><td><strong>4. Moles of HCl in the 250 cm\u00b3 flask<\/strong><\/td><td>0.0024064 mol \u00d7 (250 cm\u00b3 \u00f7 25.0 cm\u00b3)<\/td><td>0.024064 mol<\/td><\/tr>\n<tr><td><strong>5. Concentration of the original acid<\/strong><\/td><td>All of that came from 25.0 cm\u00b3 = 0.0250 dm\u00b3: c = 0.024064 mol \u00f7 0.0250 dm\u00b3<\/td><td>0.963 mol dm\u207b\u00b3 (3 s.f.)<\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<p>The <strong>direct route<\/strong> is equally acceptable and many students find it safer: concentration of the diluted acid = 0.0024064 mol \u00f7 0.0250 dm\u00b3 = 0.0963 mol dm\u207b\u00b3.<\/p><p>The original acid was ten times more concentrated, so c(original) = 0.0963 \u00d7 10 = 0.963 mol dm\u207b\u00b3.<\/p><p>Either way, the answer is quoted to <strong>3 significant figures<\/strong> because the least precise datum, the NaOH concentration 0.0800 mol dm\u207b\u00b3, has three.<\/p>\n<p>Two slips account for most lost marks. Forgetting the dilution factor gives 0.0963 mol dm\u207b\u00b3, ten times too small.<\/p><p>Dividing by 0.250 dm\u00b3 (the flask) instead of 0.0250 dm\u00b3 (the original sample) in step 5 gives the same wrong answer by a different route.<\/p><p>If the answer for &#8220;an acid of about 1 mol dm\u207b\u00b3&#8221; comes out near 0.1, look for a lost factor of ten before writing it down.<\/p>\n<div class=\"ols-key-box\">\n<p><strong>General scaling rule:<\/strong> moles in the whole flask = moles in the aliquot \u00d7 (flask volume \u00f7 aliquot volume). Write the volumes in the same unit and the factor is dimensionless.<\/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: A Diluted Diprotic Acid<\/h2>\n<p>Follow the same route for sulfuric acid, where the mole ratio is not 1 : 1.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-998\" class=\"h5p-iframe\" data-content-id=\"998\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Titration of Hydrochloric Acid Quick Choice: Diluted Sulfuric Acid\"><\/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>Starting From a Weighed Solid Standard<\/h2>\n<\/div>\n<p>On AQA the practical is often run with a <strong>primary standard<\/strong> made from a solid instead of a diluted acid.<\/p><p>Anhydrous sodium carbonate is the usual choice because it is pure, stable, non-hygroscopic and has a high molar mass, so a weighing error is a small percentage of the mass.<\/p><p>The technique is in <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/required-practicals\/rp1-making-a-volumetric-solution\/\">Required Practical 1 (preparation of a standard solution)<\/a>; the calculation is worked here.<\/p>\n<p>Sample data: 2.65 g of Na\u2082CO\u2083 (Mr 106.0) dissolved and made up to 250 cm\u00b3; 25.0 cm\u00b3 aliquots titrated with the hydrochloric acid, mean titre 23.60 cm\u00b3, methyl orange indicator.<\/p>\n<p>Na\u2082CO\u2083(aq) + 2HCl(aq) \u2192 2NaCl(aq) + H\u2082O(l) + CO\u2082(g)<\/p>\n<div class=\"ols-table-wrap\">\n<table class=\"ols-table\">\n<thead>\n<tr><th>Step<\/th><th>Working<\/th><th>Result<\/th><\/tr>\n<\/thead>\n<tbody>\n<tr><td><strong>1. Moles of Na\u2082CO\u2083 in the flask<\/strong><\/td><td>2.65 g \u00f7 106.0 g mol\u207b\u00b9<\/td><td>0.0250 mol<\/td><\/tr>\n<tr><td><strong>2. Concentration of the standard<\/strong><\/td><td>0.0250 mol \u00f7 0.250 dm\u00b3<\/td><td>0.100 mol dm\u207b\u00b3<\/td><\/tr>\n<tr><td><strong>3. Moles of Na\u2082CO\u2083 in a 25.0 cm\u00b3 aliquot<\/strong><\/td><td>0.100 mol dm\u207b\u00b3 \u00d7 0.0250 dm\u00b3<\/td><td>0.00250 mol<\/td><\/tr>\n<tr><td><strong>4. Moles of HCl in the titre<\/strong><\/td><td>2 : 1 ratio<\/td><td>0.00500 mol<\/td><\/tr>\n<tr><td><strong>5. Concentration of the acid<\/strong><\/td><td>0.00500 mol \u00f7 0.02360 dm\u00b3<\/td><td>0.212 mol dm\u207b\u00b3 (3 s.f.)<\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<p>The mole ratio is where marks go: 2 mol of HCl react with 1 mol of Na\u2082CO\u2083, so the moles of acid are double, not half, the moles of carbonate.<\/p>\n<p>Weighing by difference (weigh the bottle with solid, tip it out, weigh the bottle again) is the technique mark.<\/p>\n<p>A 2 d.p. balance contributes \u00b10.005 g per reading, \u00b10.01 g in 2.65 g, which is 0.38%.<\/p>\n\n<\/article>\n<article class=\"ols-note-card\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">10<\/div>\n<h2>Errors, Uncertainty and Improvements<\/h2>\n<\/div>\n<p>Evaluation questions want three things: the source of error, the direction it pushes the titre and the calculated concentration, and the improvement. Start with the measuring apparatus, using the uncertainty of each reading (\u00b10.05 cm\u00b3 per burette reading, \u00b10.06 cm\u00b3 for the 25 cm\u00b3 pipette, \u00b10.3 cm\u00b3 for the 250 cm\u00b3 flask).<\/p>\n<div class=\"ols-table-wrap\">\n<table class=\"ols-table\">\n<thead>\n<tr><th>Measurement<\/th><th>Reading<\/th><th>Uncertainty<\/th><th>Percentage uncertainty<\/th><\/tr>\n<\/thead>\n<tbody>\n<tr><td><strong>Burette titre (two readings)<\/strong><\/td><td>30.08 cm\u00b3<\/td><td>\u00b10.10 cm\u00b3<\/td><td>0.10 \u00f7 30.08 \u00d7 100 = 0.33%<\/td><\/tr>\n<tr><td><strong>Pipette, original acid<\/strong><\/td><td>25.0 cm\u00b3<\/td><td>\u00b10.06 cm\u00b3<\/td><td>0.06 \u00f7 25.0 \u00d7 100 = 0.24%<\/td><\/tr>\n<tr><td><strong>Pipette, aliquot of diluted acid<\/strong><\/td><td>25.0 cm\u00b3<\/td><td>\u00b10.06 cm\u00b3<\/td><td>0.24%<\/td><\/tr>\n<tr><td><strong>Volumetric flask<\/strong><\/td><td>250 cm\u00b3<\/td><td>\u00b10.3 cm\u00b3<\/td><td>0.3 \u00f7 250 \u00d7 100 = 0.12%<\/td><\/tr>\n<tr><td><strong>Total<\/strong><\/td><td><\/td><td><\/td><td>0.33 + 0.24 + 0.24 + 0.12 = 0.93%, about 1%<\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<p>The absolute uncertainty in the answer is 0.963 mol dm\u207b\u00b3 \u00d7 0.0093 = 0.009, so the result is 0.963 \u00b1 0.01 mol dm\u207b\u00b3 (round the uncertainty to one significant figure).<\/p><p>The end point itself adds up to one drop, about \u00b10.05 cm\u00b3, which is why dropwise addition and a persistent colour matter.<\/p><p>The burette dominates, and its percentage uncertainty falls as the titre grows: this is the quantitative reason the acid was diluted only tenfold and not a hundredfold. A titre of 3 cm\u00b3 would carry 0.10 \u00f7 3.00 \u00d7 100 = 3.3%.<\/p>\n<p>Improvements that examiners credit: a larger titre (a more dilute alkali or a larger aliquot), a burette with finer graduations, repeating to get more concordant titres, a pipette rather than a measuring cylinder for every fixed volume.<\/p><p>Improvements they do not credit: &#8220;be more careful&#8221;, &#8220;use more accurate equipment&#8221; without naming it, and &#8220;do more repeats&#8221; with no reason.<\/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 titre<\/th><th>Calculated concentration<\/th><th>Improvement<\/th><\/tr>\n<\/thead>\n<tbody>\n<tr><td><strong>Pipette rinsed with water<\/strong><\/td><td>Smaller: fewer moles of acid transferred<\/td><td>Too low<\/td><td>Rinse the pipette with the solution it will measure<\/td><\/tr>\n<tr><td><strong>Burette rinsed with water<\/strong><\/td><td>Larger: alkali diluted<\/td><td>Too high<\/td><td>Rinse the burette with the alkali<\/td><\/tr>\n<tr><td><strong>Pipette blown out into the volumetric or conical flask<\/strong><\/td><td>Larger: extra acid transferred<\/td><td>Too high<\/td><td>Let the pipette drain, leave the last drop<\/td><\/tr>\n<tr><td><strong>Volumetric flask overfilled past the mark<\/strong><\/td><td>Smaller: diluted acid too dilute<\/td><td>Too low<\/td><td>Add the last water dropwise; discard and repeat if overshot<\/td><\/tr>\n<tr><td><strong>Volumetric flask not inverted<\/strong><\/td><td>Scattered: aliquots not uniform<\/td><td>Random error, poor concordance<\/td><td>Stopper and invert at least ten times<\/td><\/tr>\n<tr><td><strong>Air bubble in the jet expelled during the titration<\/strong><\/td><td>Larger: bubble counted as delivered alkali<\/td><td>Too high<\/td><td>Open the tap to fill the jet before the initial reading<\/td><\/tr>\n<tr><td><strong>Funnel left in the burette<\/strong><\/td><td>Smaller: drips lower the final reading<\/td><td>Too low<\/td><td>Remove the funnel before reading<\/td><\/tr>\n<tr><td><strong>Reading the top of the meniscus every time<\/strong><\/td><td>No change: the offset cancels in final \u2212 initial<\/td><td>Unchanged<\/td><td>Read the bottom at eye level anyway, for consistency<\/td><\/tr>\n<tr><td><strong>Overshooting the end point<\/strong><\/td><td>Larger<\/td><td>Too high<\/td><td>Add dropwise near the end point, swirl, use a white tile; reject the titre<\/td><\/tr>\n<tr><td><strong>Conical flask rinsed with acid<\/strong><\/td><td>Larger: unmeasured extra acid<\/td><td>Too high<\/td><td>Rinse the conical flask with distilled water only<\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<div class=\"ols-key-box\">\n<p><strong>Exam focus:<\/strong> Always chain the argument: what changes in the flask or burette, which way the titre moves, which way the calculated concentration moves. &#8220;Titre too large&#8221; on its own is half an answer.<\/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: Evaluating a Different Titration<\/h2>\n<p>Work through the uncertainties and one error for a nitric acid titration, then decide what would improve it.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-content\" data-content-id=\"1071\"><\/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>Common Mistakes<\/h2>\n<\/div>\n<ul>\n<li>Writing HCl + NaOH \u2192 NaCl + H\u2082O without state symbols, or the ionic equation with (l) on the ions.<\/li>\n<li>Calling the sodium hydroxide a standard solution: it was standardised by titration against a primary standard.<\/li>\n<li>Leaving out why the acid was diluted: about 300 cm\u00b3 of alkali would be needed otherwise.<\/li>\n<li>Rinsing &#8220;everything with distilled water&#8221;: the pipette takes the acid, the burette takes the alkali, only the conical flask takes water.<\/li>\n<li>Including the rough titre in the mean, or averaging all the titres because &#8220;more data is better&#8221;.<\/li>\n<li>Burette readings written as 30.1 or 30.12: the second decimal place is 0 or 5.<\/li>\n<li>Getting an error direction backwards, especially a blown-out pipette: more acid means a larger titre and a concentration that is too high.<\/li>\n<li>Forgetting the factor of ten, or dividing by 0.250 dm\u00b3 instead of 0.0250 dm\u00b3, giving 0.0963 instead of 0.963 mol dm\u207b\u00b3.<\/li>\n<li>Quoting the percentage uncertainty of one burette reading (0.05 cm\u00b3) instead of the titre (0.10 cm\u00b3, two readings).<\/li>\n<li>&#8220;Persists for a few seconds&#8221; for the end point: the accepted phrase is the first permanent pale pink, persisting for about 30 s on swirling.<\/li>\n<\/ul>\n<\/article>\n<article class=\"ols-note-card\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">12<\/div>\n<h2>Common Exam Points<\/h2>\n<\/div>\n<h3>Say<\/h3><p>&#8220;Rinse the pipette with the acid so that residual water does not dilute it.&#8221; &#8220;Remove the funnel before taking the initial reading.&#8221;<\/p><p>&#8220;Concordant titres agree within 0.10 cm\u00b3 of each other; only these are averaged.&#8221;<\/p><p>&#8220;Phenolphthalein changes colour on the vertical part of the curve, so the end point coincides with the equivalence point to within one drop.&#8221;<\/p><p>&#8220;Percentage uncertainty of the titre = 0.10 \u00f7 30.08 \u00d7 100 = 0.33%.&#8221;<\/p>\n<h3>Do not say<\/h3><p>&#8220;Rinse the burette with water so it is clean.&#8221; &#8220;Add indicator until the colour is clear.&#8221; &#8220;The rough titre is included to give more results.&#8221; &#8220;A bigger flask would reduce the error.&#8221; &#8220;Blowing out the pipette makes the titre smaller.&#8221;<\/p>\n<h3>Watch for<\/h3><p>Volumes in cm\u00b3 in the question but dm\u00b3 in n = c \u00d7 V. The direction of the titration (alkali into acid) when describing the colour change.<\/p><p>The unit of the final answer, mol dm\u207b\u00b3, and its three significant figures. Whether the question wants the percentage uncertainty of a single reading or of the titre. The word &#8220;standardised&#8221; against &#8220;standard&#8221;.<\/p>\n<\/article>\n<section class=\"ols-faq-card\">\n<h2>FAQs<\/h2>\n<p>Quick answers to the questions students ask most about Required Practical 1 and its titration technique.<\/p>\n\n<div class=\"ols-faq-list\">\n<div class=\"ols-faq-item\">\n<h3>Why is the hydrochloric acid diluted before the titration?<\/h3>\n<p>The original acid is about 1 mol dm\u207b\u00b3. Titrating 25.0 cm\u00b3 of it with 0.0800 mol dm\u207b\u00b3 sodium hydroxide would need about 300 cm\u00b3 of alkali, six fillings of a 50 cm\u00b3 burette. Diluting tenfold gives a titre near 30 cm\u00b3, which fits one burette and keeps the percentage uncertainty near 0.3%.<\/p>\n<\/div>\n\n<div class=\"ols-faq-item\">\n<h3>Why can sodium hydroxide not be used as a primary standard?<\/h3>\n<p>Solid sodium hydroxide absorbs water and carbon dioxide from the air, so a weighed sample is never pure NaOH. Its solution must be standardised by titration against a primary standard such as anhydrous sodium carbonate before it can be used to find the concentration of the acid.<\/p>\n<\/div>\n\n<div class=\"ols-faq-item\">\n<h3>What counts as concordant titres on AQA?<\/h3>\n<p>Titres that agree within 0.10 cm\u00b3 of each other. The rough titre is never one of them. Only the concordant titres are averaged, and the mean is written to two decimal places.<\/p>\n<\/div>\n\n<div class=\"ols-faq-item\">\n<h3>Which way does the error go if the pipette is blown out?<\/h3>\n<p>The last drop is calibrated to stay in the pipette. Blowing it out transfers extra acid, so the flask holds more moles, the titre is larger and the calculated concentration is too high.<\/p>\n<p>Rinsing the pipette with water has the opposite effect: fewer moles, a smaller titre, a concentration that is too low.<\/p>\n<\/div>\n\n<div class=\"ols-faq-item\">\n<h3>How do I calculate the total percentage uncertainty?<\/h3>\n<p>Work out each piece of apparatus separately: burette titre 0.10 \u00f7 30.08 \u00d7 100 = 0.33%, each 25.0 cm\u00b3 pipetting 0.06 \u00f7 25.0 \u00d7 100 = 0.24% (used twice), volumetric flask 0.3 \u00f7 250 \u00d7 100 = 0.12%. Add them: 0.93%, about 1%, so the answer is 0.963 \u00b1 0.01 mol dm\u207b\u00b3.<\/p>\n<\/div>\n\n<div class=\"ols-faq-item\">\n<h3>Why is phenolphthalein suitable for this titration?<\/h3>\n<p>Its colour change over pH 8.3 to 10 lies within the vertical section of the strong acid\u2013strong base curve.<\/p><p>So one drop of alkali takes the flask from colourless to pink and the end point coincides with the equivalence point to within a drop.<\/p><p>Methyl orange also works for this pair; universal indicator does not, because it changes gradually.<\/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-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\/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\/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>. 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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phenolphthalein. This page gives the [&hellip;]<\/p>\n","protected":false},"author":12,"featured_media":0,"parent":11271,"menu_order":2,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-11274","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/pages\/11274","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/users\/12"}],"replies":[{"embeddable":true,"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/comments?post=11274"}],"version-history":[{"count":0,"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/pages\/11274\/revisions"}],"up":[{"embeddable":true,"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/pages\/11271"}],"wp:attachment":[{"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/media?parent=11274"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}