{"id":11290,"date":"2026-09-27T14:52:18","date_gmt":"2026-09-27T13:52:18","guid":{"rendered":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/practical-activity-groups\/pag-2-preparing-a-standard-solution\/"},"modified":"2026-10-03T08:38:12","modified_gmt":"2026-10-03T07:38:12","slug":"pag-2-preparing-a-standard-solution","status":"publish","type":"page","link":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/practical-activity-groups\/pag-2-preparing-a-standard-solution\/","title":{"rendered":"PAG 2 Preparing a Standard Solution"},"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; background: transparent; }\n      .ols-table, .ols-table thead, .ols-table tbody, .ols-table th, .ols-table td, .ols-table tr { display: block; width: 100%; }\n      .ols-table { border-collapse: separate; border-spacing: 0; }\n      .ols-table thead { display: none; }\n      .ols-table tr { margin-bottom: 14px; border: 1px solid var(--border); border-radius: 18px; overflow: hidden; background: #ffffff; box-shadow: var(--inner-shadow); }\n      .ols-table td { border-bottom: 1px solid var(--border); padding: 14px 16px; overflow-wrap: anywhere; }\n      .ols-table td:last-child { border-bottom: none; }\n      .ols-table td::before { content: attr(data-label); display: block; margin-bottom: 6px; font-size: 13px; font-weight: 700; color: var(--blue); }\n      .ols-author { align-items: flex-start; padding: 22px 18px; border-radius: 22px; }\n      .ols-author-avatar-img { width: 72px; height: 72px; }\n      .ols-author-title { font-size: 24px; }\n      .ols-author-description { font-size: 15px; }\n      .ols-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>OCR A A Level Chemistry<\/p>\n  <\/div>\n\n  <div class=\"ols-topic-group\">\n    <h4>Practical Activity Groups (PAGs)<\/h4>\n\n    <ul class=\"ols-topic-list\">\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/practical-activity-groups\/pag-1-molar-volume-of-a-gas\/\">PAG 1: Molar Volume of a Gas<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/practical-activity-groups\/pag-3-enthalpy-determination\/\">PAG 3: Enthalpy Change via Hess's Law<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/practical-activity-groups\/pag-2-acid-base-titration\/\">PAG 2: Concentration of HCl by Titration<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/practical-activity-groups\/pag-2-preparing-a-standard-solution\/\">PAG 2: Preparation of a Standard Solution<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/practical-activity-groups\/rates-of-hydrolysis-of-haloalkanes\/\">Hydrolysis rates: Hydrolysis of Halogenoalkanes<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/practical-activity-groups\/pag-5-synthesis-of-an-organic-liquid\/\">PAG 5: Chlorination of 2-methylpropan-2-ol<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/practical-activity-groups\/pag-5-oxidation-of-an-alcohol\/\">PAG 5: Oxidation of an Alcohol<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/practical-activity-groups\/pag-4-pag-7-qualitative-analysis-of-ions-and-functional-groups\/\">PAG 4 and 7: Analysis of Inorganic and Organic Unknowns<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/practical-activity-groups\/measuring-rates-of-reaction\/\">Rates: Rates of Reaction<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/practical-activity-groups\/pag-1-moles-determination-by-mass\/\">PAG 1: 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\/ocr-a\/\">OCR A Chemistry<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/practical-activity-groups\/\">Practical Activity Groups (PAGs)<\/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\/ocr-a\/\">OCR A<\/a> \/\n<a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/practical-activity-groups\/\">Practical Activity Groups (PAGs)<\/a> \/\n<span>PAG 2 Preparing a Standard Solution<\/span>\n<\/nav>\n\n      <header class=\"ols-title-card\">\n        <h1>PAG 2 Preparing a Standard Solution<\/h1>\n        <p class=\"ols-page-intro\">PAG 2 for OCR A A Level Chemistry: prepare a standard solution of sulfamic acid, H\u2082NSO\u2083H, by weighing by difference and making up to 250.0 cm\u00b3, then titrate it against sodium hydroxide with methyl orange. Method with reasons, corrected sample data, worked calculation to 0.0796 mol dm\u207b\u00b3, percentage uncertainties and the errors that push the answer high or low.<\/p>\n\n        <div class=\"ols-badges\">\n<div class=\"ols-badge\">Practical endorsement<\/div>\n<div class=\"ols-badge\">PAG 2<\/div>\n<div class=\"ols-badge\">H432<\/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 OCR A 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: Acids, Alkalis and Titrations<\/h2>\n<p>Four quick questions on the GCSE ideas this practical builds on: neutralisation, what a titration measures, which apparatus measures a fixed volume and how concentration is calculated.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-content\" data-content-id=\"1000\"><\/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>PAG 2 has two connected parts. First you make a <strong>standard solution<\/strong> of sulfamic acid, H\u2082NSO\u2083H (also written H\u2083NSO\u2083): a solution whose concentration is known accurately because it was made from a weighed mass of a pure solid in a known volume.<\/p><p>Then you use that acid in an acid-base titration to find the concentration of a sodium hydroxide solution.<\/p><p>The chain of reasoning is:<\/p><div class=\"ols-table-wrap\"><table class=\"ols-table\"><thead><tr><th>From<\/th><th>Gives<\/th><\/tr><\/thead><tbody><tr><td><strong>mass of solid<\/strong><\/td><td>moles of acid<\/td><\/tr><tr><td><strong>the 250.0 cm\u00b3 volumetric flask<\/strong><\/td><td>the acid concentration<\/td><\/tr><tr><td><strong>the titre<\/strong><\/td><td>the moles of acid that react with 25.0 cm\u00b3 of alkali<\/td><\/tr><tr><td><strong>the equation<\/strong><\/td><td>the moles of alkali<\/td><\/tr><tr><td><strong>the pipette volume<\/strong><\/td><td>its concentration<\/td><\/tr><\/tbody><\/table><\/div>\n<p>The relative formula mass is needed at the first step, and students lose marks by copying a wrong value: <strong>Mr(H\u2082NSO\u2083H)<\/strong> = 3 \u00d7 1.0 + 14.0 + 32.1 + 3 \u00d7 16.0 = 97.1. Sulfamic acid is <strong>monoprotic<\/strong>, so one mole of acid neutralises one mole of sodium hydroxide:<\/p>\n<p>H\u2082NSO\u2083H(aq) + NaOH(aq) \u2192 H\u2082NSO\u2083Na(aq) + H\u2082O(l)<\/p>\n<p>A solid that can be weighed out to make a standard solution directly is a <strong>primary standard<\/strong>.<\/p><p>It must be available in high purity, stable in air (not <strong>hygroscopic<\/strong> or deliquescent, and not reacting with carbon dioxide), soluble in water, and have a reasonably high Mr so that weighing errors are a small fraction of the mass.<\/p><p>Sulfamic acid meets all of these, which is why it is chosen.<\/p><p>Sodium hydroxide fails the test: the pellets absorb water and carbon dioxide from the air while they sit on the balance, so their mass never gives their moles. Its concentration has to be found by titration against a primary standard instead.<\/p>\n<p>The skills are examined in the written papers (practical skills are examined in every paper) and the practical endorsement.<\/p>\n<p>On this practical that means being able to describe weighing by difference, the transfer with washings, the volumetric flask technique, the titration technique, and the choice of indicator and its colour change.<\/p>\n<p>It also means the treatment of titres, the calculation to 3 significant figures and the percentage uncertainty of each measurement.<\/p>\n<div class=\"ols-key-box\">\n<p><strong>Key idea:<\/strong> A standard solution is made from a primary standard: pure, stable, weighable. Every rinse, reading and volume in this practical feeds straight into the final concentration, so every technique point has a calculation consequence.<\/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 a Primary Standard<\/h2>\n<p>Decide which solids could be weighed out to make a standard solution, and why the others cannot.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-1001\" class=\"h5p-iframe\" data-content-id=\"1001\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Standard Solution Quick Choice: Choosing a Primary Standard\"><\/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>Sulfamic acid is an <strong>irritant<\/strong> to the skin and eyes. Sodium hydroxide at about 0.1 mol dm\u207b\u00b3 is also an irritant (it is classed as corrosive above about 0.5 mol dm\u207b\u00b3).<\/p><p>Wear eye protection throughout, avoid skin contact with both solutions and wash any spill off the skin with plenty of water.<\/p><p>Fill the burette <strong>below eye level<\/strong> using a small funnel so that acid cannot splash into your face, and remove the funnel before taking a reading. Clamp the burette firmly: a full burette in a loose clamp can tip and shatter.<\/p>\n<div class=\"ols-table-wrap\">\n<table class=\"ols-table\">\n<thead>\n<tr><th>Apparatus<\/th><th>What it is for<\/th><th>Precision<\/th><\/tr>\n<\/thead>\n<tbody>\n<tr><td><strong>Balance reading to 0.01 g<\/strong><\/td><td>Weighing the sulfamic acid by difference<\/td><td>\u00b10.005 g on each reading, so \u00b10.01 g on the mass used<\/td><\/tr>\n<tr><td><strong>Weighing bottle (or small beaker)<\/strong><\/td><td>Holding the solid on the balance and while it is tipped out<\/td><td>Reweighed with any residue<\/td><\/tr>\n<tr><td><strong>250 cm\u00b3 beaker and glass rod<\/strong><\/td><td>Dissolving the solid in about 100 cm\u00b3 of distilled water<\/td><td>Volume is approximate at this stage<\/td><\/tr>\n<tr><td><strong>Funnel, wash bottle of distilled water<\/strong><\/td><td>Transferring the solution and every washing into the flask<\/td><td>Rinsing loses no solute<\/td><\/tr>\n<tr><td><strong>250 cm\u00b3 volumetric flask<\/strong><\/td><td>Making the solution up to exactly 250.0 cm\u00b3<\/td><td>\u00b10.15 cm\u00b3 (class A) or \u00b10.30 cm\u00b3 (class B)<\/td><\/tr>\n<tr><td><strong>Dropping pipette<\/strong><\/td><td>Adding the last drops of water to the mark<\/td><td>Prevents overshooting<\/td><\/tr>\n<tr><td><strong>50 cm\u00b3 burette, clamp and stand<\/strong><\/td><td>Delivering the sulfamic acid solution and measuring the titre<\/td><td>\u00b10.05 cm\u00b3 on each reading, recorded to 0.05 cm\u00b3<\/td><\/tr>\n<tr><td><strong>25.0 cm\u00b3 volumetric pipette and filler<\/strong><\/td><td>Measuring the sodium hydroxide into the conical flask<\/td><td>\u00b10.06 cm\u00b3<\/td><\/tr>\n<tr><td><strong>250 cm\u00b3 conical flask on a white tile<\/strong><\/td><td>Holding the alkali and indicator; the tile shows the colour change<\/td><td>Swirled, not stirred<\/td><\/tr>\n<tr><td><strong>Methyl orange<\/strong><\/td><td>Indicator: yellow in the alkali, orange at the end point<\/td><td>2 to 3 drops only<\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<div class=\"ols-key-box\">\n<p><strong>Exam wording:<\/strong> Hazard questions want the classification and the precaution together: &#8220;sulfamic acid is an irritant, so wear eye protection and wash spills off the skin with water&#8221;.<\/p><p>A hazard is not the same as a risk: the hazard is the property, the risk is the chance of harm in this procedure.<\/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 has nine steps. Each one carries its reason, because the reasons are what the mark scheme rewards: &#8220;rinse the beaker&#8221; scores nothing on its own, &#8220;rinse the beaker so that all of the acid reaches the flask&#8221; scores the mark.<\/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 Weigh by difference<\/strong><\/td><td>Put about 2.5 g of sulfamic acid into a weighing bottle and record the mass of bottle plus acid, m\u2081. Tip the acid into a 250 cm\u00b3 beaker and reweigh the bottle with any residue, m\u2082. Mass used = m\u2081 \u2212 m\u2082.<\/td><td>The mass that actually reached the beaker is what is recorded, so grains left in the bottle do not matter. About 2.5 g in 250 cm\u00b3 gives a concentration close to 0.1 mol dm\u207b\u00b3, a good match to the alkali.<\/td><\/tr>\n<tr><td><strong>2 Dissolve<\/strong><\/td><td>Add about 100 cm\u00b3 of distilled water and stir with a glass rod until all the solid has dissolved. If the beaker was warmed, let it cool to room temperature.<\/td><td>Undissolved solid cannot be transferred as solution. A warm solution contracts on cooling, so a flask filled warm would end below the mark.<\/td><\/tr>\n<tr><td><strong>3 Transfer with washings<\/strong><\/td><td>Pour the solution through a funnel into a 250 cm\u00b3 volumetric flask. Rinse the beaker, the glass rod and the funnel with distilled water from a wash bottle and add every rinsing to the flask.<\/td><td>Every mole of acid weighed out must end up in the flask, otherwise the calculated concentration is higher than the real one.<\/td><\/tr>\n<tr><td><strong>4 Make up to the mark<\/strong><\/td><td>Add distilled water until the level is about 1 cm below the line, then add the last drops with a dropping pipette until the bottom of the meniscus sits exactly on the calibration line, viewed at eye level.<\/td><td>The flask is calibrated to contain 250.0 cm\u00b3 at 20 \u00b0C when filled to the line. Reading at eye level avoids parallax error.<\/td><\/tr>\n<tr><td><strong>5 Mix<\/strong><\/td><td>Stopper the flask and invert it about ten times.<\/td><td>The concentration must be the same in every part of the solution, or different portions run from the burette would have different concentrations.<\/td><\/tr>\n<tr><td><strong>6 Prepare the burette<\/strong><\/td><td>Rinse the burette with a little of the sulfamic acid solution and drain it. Fill it through a funnel below eye level, remove the funnel, open the tap to fill the jet, and read the initial volume from the bottom of the meniscus.<\/td><td>Water left in the burette would dilute the acid. A drip from the funnel would change the initial reading, and an air bubble in the jet would count as acid delivered and make the titre too large.<\/td><\/tr>\n<tr><td><strong>7 Pipette the alkali<\/strong><\/td><td>Rinse a 25.0 cm\u00b3 volumetric pipette with the sodium hydroxide solution, then use a pipette filler to draw the alkali up to the line and run 25.0 cm\u00b3 into a clean conical flask, touching the tip on the inside of the flask. Do not blow out the last drop.<\/td><td>Water in the pipette would dilute the alkali and reduce the moles transferred. The pipette is calibrated to deliver 25.0 cm\u00b3 with the last drop left in the tip.<\/td><\/tr>\n<tr><td><strong>8 Titrate<\/strong><\/td><td>Add 2 to 3 drops of methyl orange (the flask turns yellow) and stand it on a white tile. Do a rough titration quickly, then repeat adding the acid dropwise near the end point with constant swirling until the first permanent orange colour. Rinse the sides of the flask with distilled water near the end point. Record the final reading to 0.05 cm\u00b3.<\/td><td>The rough titre shows where the end point is so that accurate titrations can be run dropwise. Swirling mixes the acid in; washing the sides returns splashed alkali to the reaction. Extra water in the flask does not change the moles of alkali.<\/td><\/tr>\n<tr><td><strong>9 Repeat<\/strong><\/td><td>Repeat until two accurate titres are concordant, within 0.10 cm\u00b3 of each other, and average only those.<\/td><td>Concordant titres show the end point has been judged consistently; the rough titre is never included in the mean.<\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<div class=\"ols-key-box\">\n<p><strong>Technique point:<\/strong> Rinse each piece of glassware with the solution it will hold: burette with the acid, pipette with the alkali. Rinse with distilled water only where extra water does not matter: the conical flask and the volumetric flask before use.<\/p>\n<\/div>\n<\/article>\n<!-- 3D card: standard-solution-titration (27 Sep 2026) -->\n<!-- Copyright (c) 2026 Dr. Mohammed Al-Fatah, onlinelearningsystem.net. All rights reserved. -->\n<section class=\"ols-sst-001\" id=\"olsSst001\">\n<style>\n@import url('https:\/\/fonts.googleapis.com\/css2?family=Poppins:wght@300;400;500;600&display=swap');\n\n.ols-sst-001{\n  font-family:'Poppins',system-ui,-apple-system,'Segoe UI',Roboto,Helvetica,Arial,sans-serif;\n  color:#1C244B; background:#ffffff;\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:44px; margin:26px auto; max-width:980px;\n  box-sizing:border-box; -webkit-font-smoothing:antialiased;\n}\n.ols-sst-001 *{box-sizing:border-box;}\n\n.ols-sst-001 .sst-head{margin:0 0 22px;}\n.ols-sst-001 h2.sst-title{\n  font-size:26px; line-height:1.25; font-weight:600; letter-spacing:-0.012em;\n  margin:0 0 9px; color:#1C244B;\n}\n.ols-sst-001 p.sst-sub{\n  font-size:14.5px; line-height:1.62; font-weight:300; color:#4a5270;\n  margin:0; max-width:68ch;\n}\n\n.ols-sst-001 .sst-stage{\n  position:relative; width:100%; height:600px;\n  background:#ffffff; border:1px solid rgba(28,36,75,0.12);\n  border-radius:18px; overflow:hidden; outline:none;\n}\n.ols-sst-001 .sst-stage:focus-visible{box-shadow:0 0 0 2px #2563eb;}\n.ols-sst-001 .sst-canvas{\n  display:block; width:100%; height:100%;\n  touch-action:none; cursor:pointer; background:#ffffff;\n}\n.ols-sst-001 .sst-canvas.is-paused{cursor:grab;}\n.ols-sst-001 .sst-canvas.is-drag{cursor:grabbing;}\n.ols-sst-001 .sst-overlay{position:absolute; inset:0; pointer-events:none; overflow:hidden;}\n\n\/* object labels *\/\n.ols-sst-001 .sst-lab{\n  position:absolute; left:0; top:0; display:none;\n  white-space:normal; max-width:230px; font-size:12px; font-weight:500; line-height:1.3;\n  padding:4px 10px; background:rgba(255,255,255,0.95);\n  border:1px solid rgba(28,36,75,0.22); border-radius:12px;\n  color:#1C244B; will-change:transform,opacity; font-variant-numeric:tabular-nums;\n}\n\/* call-out cards *\/\n.ols-sst-001 .sst-co{\n  position:absolute; left:0; top:0; display:none;\n  max-width:260px; padding:7px 12px 8px 11px;\n  background:#ffffff; border:1px solid rgba(28,36,75,0.14); border-left:4px solid #c9961c;\n  border-radius:10px; box-shadow:0 8px 22px rgba(28,36,75,0.13);\n  font-size:12.5px; font-weight:400; line-height:1.45; color:#1C244B;\n  will-change:transform,opacity;\n}\n.ols-sst-001 .sst-co .co-t{\n  display:block; font-size:10.5px; font-weight:600; letter-spacing:0.05em;\n  text-transform:uppercase; color:#8a6410; margin-bottom:2px;\n}\n.ols-sst-001 .sst-co.co-warn{border-left-color:#cc3a2f;}\n.ols-sst-001 .sst-co.co-warn .co-t{color:#b0271d;}\n.ols-sst-001 .sst-co b{font-weight:600;}\n.ols-sst-001 .sst-co.co-wide{max-width:none;}\n.ols-sst-001 .sst-co ul{margin:3px 0 0; padding-left:17px;}\n.ols-sst-001 .sst-co li{margin:0 0 4px;}\n.ols-sst-001 .sst-co .cl{padding:5px 0; border-top:1px solid rgba(28,36,75,0.08);}\n.ols-sst-001 .sst-co .cl:first-of-type{border-top:0;}\n.ols-sst-001 .sst-co .ck{display:block; font-size:11px; color:#6b7290; font-weight:500;}\n.ols-sst-001 .sst-co .big{display:block; font-size:17px; font-weight:600; color:#0e6f6b;}\n.ols-sst-001 .sst-co .nt{display:block; margin-top:3px; font-size:11px; color:#6b7290;}\n\n.ols-sst-001 .sst-subt{\n  position:absolute; left:0; bottom:12px; max-width:640px;\n  font-size:14px; font-weight:500; line-height:1.42; text-align:center;\n  color:#ffffff; background:rgba(28,36,75,0.88);\n  padding:7px 14px; border-radius:12px; pointer-events:none;\n}\n.ols-sst-001 .sst-hint{\n  position:absolute; right:14px; top:14px;\n  font-size:11.5px; font-weight:400; color:#6b7290;\n  background:rgba(255,255,255,0.94); padding:5px 11px;\n  border-radius:999px; border:1px solid rgba(28,36,75,0.12); pointer-events:none;\n}\n.ols-sst-001 .sst-hint[hidden]{display:none;}\n.ols-sst-001 .sst-poster{\n  position:absolute; left:50%; top:50%; width:92px; height:92px; margin:-46px 0 0 -46px;\n  border:0; border-radius:50%; padding:0; cursor:pointer;\n  background:rgba(28,36,75,0.9); color:#ffffff;\n  display:flex; flex-direction:column; align-items:center; justify-content:center;\n  box-shadow:0 12px 30px rgba(28,36,75,0.35); font-family:inherit; font-size:11.5px; font-weight:600;\n  transition:background .15s, transform .15s;\n}\n.ols-sst-001 .sst-poster:hover{background:#c9961c; transform:scale(1.04);}\n.ols-sst-001 .sst-poster:focus-visible{outline:3px solid #c9961c; outline-offset:3px;}\n.ols-sst-001 .sst-poster svg{width:40px; height:40px; fill:#ffffff; margin-left:5px;}\n.ols-sst-001 .sst-poster.is-replay svg{margin-left:0; width:34px; height:34px;}\n.ols-sst-001 .sst-poster span{display:none; margin-top:1px;}\n.ols-sst-001 .sst-poster.is-replay span{display:block;}\n.ols-sst-001 .sst-poster[hidden]{display:none;}\n\n\/* the player bar *\/\n.ols-sst-001 .sst-player{\n  margin-top:10px; background:#1C244B; color:#ffffff; border-radius:14px;\n  padding:8px 12px; display:flex; align-items:center; flex-wrap:wrap; gap:4px 6px;\n}\n.ols-sst-001 .sst-pb{\n  font-family:inherit; flex:0 0 auto; width:38px; height:38px; padding:0;\n  display:inline-flex; align-items:center; justify-content:center;\n  background:transparent; border:0; border-radius:9px; color:#ffffff; cursor:pointer;\n  transition:background .15s;\n}\n.ols-sst-001 .sst-pb:hover{background:rgba(255,255,255,0.12);}\n.ols-sst-001 .sst-pb:focus-visible{outline:2px solid #c9961c; outline-offset:1px;}\n.ols-sst-001 .sst-pb svg{width:22px; height:22px; fill:currentColor;}\n.ols-sst-001 .sst-pb svg text{font-family:inherit; font-size:7.5px; font-weight:600; fill:currentColor;}\n.ols-sst-001 .sst-speed{width:auto; min-width:54px; padding:0 10px; font-size:13px; font-weight:600;}\n.ols-sst-001 .sst-prog{\n  position:relative; flex:1 1 160px; min-width:120px; height:30px; margin:0 6px;\n  cursor:pointer; touch-action:none; outline:none;\n}\n.ols-sst-001 .sst-track{position:absolute; left:0; right:0; top:13px; height:5px; border-radius:3px; background:rgba(255,255,255,0.25); overflow:hidden;}\n.ols-sst-001 .sst-fill{height:100%; width:0; background:#c9961c;}\n.ols-sst-001 .sst-thumb{\n  position:absolute; left:0; top:9px; width:13px; height:13px; margin-left:-6.5px;\n  border-radius:50%; background:#c9961c; box-shadow:0 0 0 2px #1C244B; pointer-events:none;\n}\n.ols-sst-001 .sst-prog:focus-visible .sst-thumb{box-shadow:0 0 0 2px #ffffff;}\n.ols-sst-001 .sst-tick{\n  position:absolute; top:7px; width:12px; height:17px; margin-left:-6px; padding:0;\n  background:transparent; border:0; cursor:pointer; outline:none;\n}\n.ols-sst-001 .sst-tick::before{\n  content:''; position:absolute; left:5px; top:4px; width:2px; height:9px;\n  border-radius:1px; background:rgba(255,255,255,0.8);\n}\n.ols-sst-001 .sst-tick:focus-visible::before{background:#c9961c; width:3px; left:4.5px;}\n.ols-sst-001 .sst-tick .tt{\n  display:none; position:absolute; bottom:22px; left:50%; transform:translateX(-50%);\n  background:#ffffff; color:#1C244B; font-size:11.5px; font-weight:600; white-space:nowrap;\n  padding:3px 9px; border-radius:7px; box-shadow:0 4px 14px rgba(28,36,75,0.25); pointer-events:none;\n}\n.ols-sst-001 .sst-tick.tt-l .tt{left:0; transform:none;}\n.ols-sst-001 .sst-tick.tt-r .tt{left:auto; right:0; transform:none;}\n.ols-sst-001 .sst-tick:hover .tt,.ols-sst-001 .sst-tick:focus-visible .tt{display:block;}\n.ols-sst-001 .sst-time{flex:0 0 auto; padding:0 4px; font-size:12.5px; font-weight:500; white-space:nowrap; font-variant-numeric:tabular-nums;}\n\n.ols-sst-001 .sst-chips{margin-top:10px; display:flex; flex-wrap:wrap; gap:6px;}\n.ols-sst-001 .sst-chip{\n  font-family:inherit; font-size:12.5px; font-weight:500; color:#3c4463;\n  background:#fbfbfd; border:1px solid rgba(28,36,75,0.16); border-radius:999px;\n  padding:6px 12px; cursor:pointer; transition:background .15s, border-color .15s, color .15s;\n}\n.ols-sst-001 .sst-chip i{font-style:normal; font-weight:600; opacity:0.55; margin-right:5px;}\n.ols-sst-001 .sst-chip:hover{border-color:rgba(201,150,28,0.7);}\n.ols-sst-001 .sst-chip:focus-visible{outline:2px solid #2563eb; outline-offset:2px;}\n.ols-sst-001 .sst-chip[aria-current=\"true\"]{background:#1C244B; border-color:#1C244B; color:#ffffff;}\n.ols-sst-001 .sst-chip[aria-current=\"true\"] i{opacity:1; color:#c9961c;}\n\n\/* narrow stage (set from the script by the stage width) *\/\n.ols-sst-001 .sst-narrow .sst-co{max-width:170px; font-size:10.5px; line-height:1.38; padding:5px 8px 6px 8px; border-left-width:3px; border-radius:8px;}\n.ols-sst-001 .sst-narrow .sst-co .co-t{font-size:9px; margin-bottom:1px;}\n.ols-sst-001 .sst-narrow .sst-co .cl{padding:3px 0;}\n.ols-sst-001 .sst-narrow .sst-co .ck{display:inline; font-size:9.5px; margin-right:4px;}\n.ols-sst-001 .sst-narrow .sst-co .big{font-size:13.5px;}\n.ols-sst-001 .sst-narrow .sst-co .nt{font-size:9.5px;}\n.ols-sst-001 .sst-narrow .sst-co ul{padding-left:14px;}\n.ols-sst-001 .sst-narrow .sst-co li{margin-bottom:2px;}\n.ols-sst-001 .sst-narrow .sst-co.co-wide{max-width:none;}\n.ols-sst-001 .sst-narrow .sst-lab{font-size:10.5px; padding:3px 7px; max-width:140px; border-radius:9px;}\n.ols-sst-001 .sst-narrow .sst-subt{font-size:11.5px; padding:5px 10px; border-radius:10px; bottom:10px;}\n.ols-sst-001 .sst-narrow .sst-poster{width:74px; height:74px; margin:-37px 0 0 -37px;}\n.ols-sst-001 .sst-narrow .sst-poster svg{width:32px; height:32px;}\n\n@media (max-width:760px){\n  .ols-sst-001{padding:26px; border-radius:22px;}\n  .ols-sst-001 h2.sst-title{font-size:20.5px;}\n  .ols-sst-001 p.sst-sub{font-size:13.5px;}\n  .ols-sst-001 .sst-stage{height:560px;}\n}\n@media (max-width:560px){\n  .ols-sst-001 .sst-player{padding:6px 8px;}\n  .ols-sst-001 .sst-prog{order:-1; flex:1 1 100%; margin:0 4px;}\n  .ols-sst-001 .sst-pb{width:36px; height:36px;}\n  .ols-sst-001 .sst-time{margin-right:auto;}\n  .ols-sst-001 .sst-chip{font-size:11.5px; padding:5px 10px;}\n}\n@media (max-width:480px){\n  .ols-sst-001{padding:14px; border-radius:18px;}\n  .ols-sst-001 .sst-head{margin-bottom:14px;}\n}\n@media (prefers-reduced-motion:reduce){\n  .ols-sst-001 .sst-poster,.ols-sst-001 .sst-chip,.ols-sst-001 .sst-pb{transition:none;}\n}\n\n\/* full screen: the card fills the screen and the stage takes the spare height *\/\n.ols-sst-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-sst-001:fullscreen .sst-head{display:none;}\n.ols-sst-001:fullscreen .sst-stage{flex:1 1 auto; height:auto; min-height:320px;}\n.ols-sst-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-sst-001:-webkit-full-screen .sst-head{display:none;}\n.ols-sst-001:-webkit-full-screen .sst-stage{flex:1 1 auto; height:auto; min-height:320px;}\n\n.ols-cc-sst-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-sst-001 a{color:#aab0c0; text-decoration:none;}\n.ols-cc-sst-001 a:hover{text-decoration:underline;}\n<\/style>\n\n<div class=\"sst-head\">\n  <h2 class=\"sst-title\">Standard Solution and Titration<\/h2>\n  <p class=\"sst-sub\">Make a 250 cm\u00b3 standard solution of sulfamic acid, H\u2082NSO\u2083H, by weighing by difference, then titrate it against sodium hydroxide to find the concentration of the alkali.<\/p>\n<\/div>\n\n<div class=\"sst-stage\" id=\"sstStage\" tabindex=\"0\" aria-label=\"Film of the practical. Space plays or pauses, the left and right arrow keys skip 10 seconds.\">\n  <canvas class=\"sst-canvas\" id=\"sstCanvas\" aria-hidden=\"true\"><\/canvas>\n  <div class=\"sst-overlay\" id=\"sstOverlay\"><\/div>\n  <div class=\"sst-subt\" id=\"sstSubt\"><\/div>\n  <div class=\"sst-hint\" id=\"sstHint\" hidden>Paused: drag to look around<\/div>\n  <button type=\"button\" class=\"sst-poster\" id=\"sstPoster\" 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=\"sst-player\" id=\"sstPlayer\" role=\"group\" aria-label=\"Film controls\">\n  <button type=\"button\" class=\"sst-pb\" id=\"sstPlay\" 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=\"sst-pb\" id=\"sstBack\" 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=\"sst-pb\" id=\"sstFwd\" 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=\"sst-pb\" id=\"sstRestart\" 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=\"sst-prog\" id=\"sstProg\" role=\"slider\" tabindex=\"0\" aria-label=\"Seek\" aria-valuemin=\"0\" aria-valuemax=\"214\" aria-valuenow=\"0\" aria-valuetext=\"0:00\">\n    <div class=\"sst-track\"><div class=\"sst-fill\" id=\"sstFill\"><\/div><\/div>\n    <div class=\"sst-thumb\" id=\"sstThumb\"><\/div>\n  <\/div>\n  <span class=\"sst-time\" id=\"sstTime\">0:00 \/ 3:34<\/span>\n  <button type=\"button\" class=\"sst-pb sst-speed\" id=\"sstSpeed\" aria-label=\"Playback speed 1\u00d7\">1\u00d7<\/button>\n  <button type=\"button\" class=\"sst-pb\" id=\"sstFs\" 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=\"sst-chips\" id=\"sstChips\" role=\"group\" aria-label=\"Chapters\"><\/div>\n<\/section>\n\n<p class=\"ols-cc-sst-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\/standard-solution-titration.js?v=20260928b\"><\/script>\n\n<section class=\"ols-h5p-card ols-h5p-inline\">\n<span class=\"ols-h5p-kicker\">Check your understanding<\/span>\n<h2>Check: Order the Method<\/h2>\n<p>Put the steps of a standard-solution preparation in a workable order for a different solid.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-1002\" class=\"h5p-iframe\" data-content-id=\"1002\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Standard Solution Order: Making a Standard Solution from a Solid\"><\/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>Preparing the Standard Solution: Sample Data<\/h2>\n<\/div>\n<p>Weighing by difference gives the mass that really reached the beaker.<\/p><p>In the sample run the weighing bottle plus sulfamic acid read <strong>m\u2081 = 14.86 g<\/strong>; after the solid had been tipped into the beaker the bottle plus residue read <strong>m\u2082 = 12.45 g<\/strong>.<\/p><p>Mass of sulfamic acid used = 14.86 \u2212 12.45 = 2.41 g.<\/p><div class=\"ols-key-box\"><p><strong>Common mistake:<\/strong> Students lose marks by weighing the bottle empty first and then assuming every grain was transferred: the residue left behind is exactly what the m\u2081 \u2212 m\u2082 method allows for.<\/p><\/div>\n<p>The solid was dissolved in about 100 cm\u00b3 of distilled water, transferred with washings and made up to 250.0 cm\u00b3. Two sums follow, and they are the first two steps of the full calculation later on the page:<\/p>\n<p>n(H\u2082NSO\u2083H) = m \u00f7 Mr = 2.41 g \u00f7 97.1 g mol\u207b\u00b9 = 0.02482 mol (carry the unrounded value)<\/p>\n<p>c(H\u2082NSO\u2083H) = n \u00f7 V = 0.02482 mol \u00f7 0.2500 dm\u00b3 = 0.0993 mol dm\u207b\u00b3 (3 s.f.)<\/p>\n<p>Notice that the volume is written in dm\u00b3 before it is used: 250.0 cm\u00b3 \u00f7 1000 = 0.2500 dm\u00b3. If the rounded 0.0248 mol were divided by 0.250 dm\u00b3 the answer would come out as 0.0992 mol dm\u207b\u00b3, so keep one extra figure until the final answer and round once.<\/p>\n<div class=\"ols-table-wrap\">\n<table class=\"ols-table\">\n<thead>\n<tr><th>Technique<\/th><th>Why it is done<\/th><th>What goes wrong if it is skipped<\/th><\/tr>\n<\/thead>\n<tbody>\n<tr><td><strong>Reweigh the bottle with its residue<\/strong><\/td><td>Records the mass actually transferred<\/td><td>Assuming the full mass was transferred gives too many moles, so the calculated acid concentration is too high<\/td><\/tr>\n<tr><td><strong>Rinse the beaker, rod and funnel into the flask<\/strong><\/td><td>Every mole of acid weighed out reaches the flask<\/td><td>Lost acid means fewer moles in the flask; the real concentration is lower than the calculated one, so the titre is larger and the calculated alkali concentration is too high<\/td><\/tr>\n<tr><td><strong>Make up to the mark exactly<\/strong><\/td><td>Fixes the volume at 250.0 cm\u00b3, the value used in the calculation<\/td><td>Filling above the mark dilutes the acid, but the student still uses 250.0 cm\u00b3, so the calculated acid concentration is too high and so is the calculated alkali concentration<\/td><\/tr>\n<tr><td><strong>Invert the flask about ten times<\/strong><\/td><td>Makes the concentration uniform<\/td><td>Poorly mixed solution gives titres that do not agree<\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<div class=\"ols-key-box\">\n<p><strong>Exam focus:<\/strong> A lost washing and an overfilled flask have the same direction of error: the acid in the flask is weaker than the calculation assumes, the titre gets bigger, and the alkali concentration comes out too high. Say which value is wrong and in which direction.<\/p>\n<\/div>\n<\/article>\n<article class=\"ols-note-card\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">5<\/div>\n<h2>Using the Volumetric Flask Correctly<\/h2>\n<\/div>\n<p>A volumetric flask has a single <strong>calibration line<\/strong> on its narrow neck. It is calibrated to contain 250.0 cm\u00b3 at 20 \u00b0C when the bottom of the meniscus sits exactly on that line.<\/p><p>The narrow neck is what makes it precise, because a small error in height is a very small error in volume.<\/p><p>A 250 cm\u00b3 measuring cylinder, by contrast, has an uncertainty of about \u00b11 cm\u00b3 or more, which is why it is never used to make a standard solution.<\/p>\n<p>Fill to about 1 cm below the line with the wash bottle, then finish with a dropping pipette so that you cannot overshoot.<\/p><p>Read the mark with your eye level with the line: looking down on it makes the meniscus appear too high and causes <strong>parallax error<\/strong>.<\/p><p>If the level does go above the line the solution must be thrown away and the preparation started again, because there is no way of knowing how much extra water was added.<\/p>\n<p>Never heat a volumetric flask or pour a warm solution into it. The reason is the liquid, not the glass.<\/p><p>A warm solution <strong>contracts<\/strong> as it cools, so a flask filled to the line while warm ends up below the line at 20 \u00b0C, the volume is less than 250.0 cm\u00b3 and the concentration is higher than the calculation says.<\/p><p>Glass expansion is a much smaller effect. Cool the beaker to room temperature before transferring.<\/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\/fix-2.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-2.jpg\" alt=\"Using a 250 cm\u00b3 volumetric flask: calibration line, meniscus read at eye level, cooling before filling, stoppering and inverting\">\n<\/a>\n<\/div>\n<div class=\"ols-zoom-card-caption\"><p>Volumetric flask technique: calibrated to contain 250.0 cm\u00b3 at 20 \u00b0C, bottom of the meniscus on the line at eye level, cool the solution before filling, stopper and invert to mix.<\/p><\/div>\n<\/div>\n<div class=\"ols-key-box\">\n<p><strong>Exam wording:<\/strong> Say &#8220;make up to the mark with distilled water&#8221;, never &#8220;fill it up&#8221;. Say &#8220;the bottom of the meniscus on the calibration line at eye level&#8221; and, for a warm solution, &#8220;the liquid contracts on cooling so the volume falls below the mark&#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: Concentration from a Weighing<\/h2>\n<p>Turn a pair of weighings and a flask volume into a concentration for a different primary standard, then predict the effect of a lost washing.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-content\" data-content-id=\"1003\"><\/div><\/div>\n<\/section>\n<article class=\"ols-note-card\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">6<\/div>\n<h2>Carrying Out the Titration<\/h2>\n<\/div>\n<p>The sulfamic acid solution goes in the <strong>burette<\/strong>; 25.0 cm\u00b3 of sodium hydroxide measured with a volumetric pipette goes in the conical flask with 2 to 3 drops of <strong>methyl orange<\/strong>.<\/p><p>Methyl orange is yellow in alkali and red in acid, so the flask starts yellow and the end point is the first <strong>permanent orange<\/strong>. Going on to red means the end point has been passed and the titre is too large.<\/p><div class=\"ols-key-box\"><p><strong>Exam tip:<\/strong> The indicator colour change is a certain mark in the practical paper and the live page never gave it; write it out as &#8220;yellow to orange&#8221;.<\/p><\/div>\n<p>Technique points that score: rinse the burette with the acid and the pipette with the alkali; fill the burette below eye level and remove the funnel before reading; make sure the jet below the tap is full of acid.<\/p><p>Read the <strong>bottom of the meniscus<\/strong> at eye level and record to 0.05 cm\u00b3; stand the flask on a white tile; run a rough titration first.<\/p><p>Near the end point add acid drop by drop with continuous swirling and rinse the sides of the flask with distilled water; repeat until two titres are concordant, within 0.10 cm\u00b3 of each other.<\/p>\n<p>Water in the conical flask does not matter: the moles of sodium hydroxide were fixed when 25.0 cm\u00b3 was pipetted, and extra water only dilutes them without changing their number.<\/p><p>Water in the pipette or the burette does matter, because it dilutes a solution before its volume is measured.<\/p><div class=\"ols-key-box\"><p><strong>Common mistake:<\/strong> Students lose marks by drying the conical flask &#8220;to be accurate&#8221; and by rinsing the pipette with water only.<\/p><\/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-std-titration.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-std-titration.jpg\" alt=\"Titration set-up: burette of sulfamic acid over a conical flask of 25.0 cm\u00b3 NaOH with methyl orange, meniscus zoom, funnel removed, colour sequence yellow, orange, red\">\n<\/a>\n<\/div>\n<div class=\"ols-zoom-card-caption\"><p>The titration set-up: sulfamic acid in the burette read from the bottom of the meniscus with the funnel removed, 25.0 cm\u00b3 of sodium hydroxide and methyl orange in the flask on a white tile, and the yellow, orange and red colour sequence.<\/p><\/div>\n<\/div>\n<div class=\"ols-key-box\">\n<p><strong>Why only 2 to 3 drops:<\/strong> Indicators are weak acids, so each drop reacts with a little of the sodium hydroxide and makes the titre slightly larger; a heavy colour also hides the exact moment the end point is reached.<\/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: Indicator Colour Changes<\/h2>\n<p>Place the right colours on methyl orange and phenolphthalein titrations run in either direction.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-1004\" class=\"h5p-iframe\" data-content-id=\"1004\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Standard Solution Drag: Indicator Colour Changes\"><\/iframe><\/div><\/div>\n<\/section>\n<article class=\"ols-note-card soft\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">7<\/div>\n<h2>From Burette Readings to Titres<\/h2>\n<\/div>\n<p>A titre is the volume delivered from the burette: titre = final burette reading \u2212 initial burette reading. Every reading is recorded to 0.05 cm\u00b3, so titres are quoted to 2 d.p.<\/p><p>The first titration is a <strong>rough titre<\/strong>, run quickly to locate the end point; it is labelled as such and is never used in the mean, even if it happens to be close.<\/p><p><strong>Concordant<\/strong> titres are accurate titres that agree within 0.10 cm\u00b3 of each other; only those are averaged, and the mean is quoted to 2 d.p.<\/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 in mean?<\/th><\/tr>\n<\/thead>\n<tbody>\n<tr><td><strong>Rough<\/strong><\/td><td>0.25<\/td><td>21.00<\/td><td>20.75<\/td><td>No: rough titre<\/td><\/tr>\n<tr><td><strong>2<\/strong><\/td><td>21.00<\/td><td>41.00<\/td><td>20.00<\/td><td>Yes<\/td><\/tr>\n<tr><td><strong>3<\/strong><\/td><td>0.50<\/td><td>20.85<\/td><td>20.35<\/td><td>No: not concordant<\/td><\/tr>\n<tr><td><strong>4<\/strong><\/td><td>20.85<\/td><td>40.95<\/td><td>20.10<\/td><td>Yes<\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<p>Mean titre = (20.00 + 20.10) \u00f7 2 = <strong>20.05 cm\u00b3<\/strong>.<\/p><p>Titre 3 is 0.35 cm\u00b3 above titre 2 and 0.25 cm\u00b3 above titre 4, so it fails the concordance test on either common rule and is left out.<\/p><div class=\"ols-key-box\"><p><strong>Common mistake:<\/strong> Students lose marks by averaging all four values (which gives 20.30 cm\u00b3) or by treating &#8220;concordant&#8221; as &#8220;identical&#8221;: two titres do not have to match exactly, they have to fall within the stated limit.<\/p><\/div>\n<div class=\"ols-key-box\">\n<p><strong>Exam wording:<\/strong> &#8220;Titres 2 and 4 are concordant because they agree within 0.10 cm\u00b3 of each other; the rough titre and titre 3 are not used. Mean titre = 20.05 cm\u00b3.&#8221; Name the titres used and give the mean to 2 d.p.<\/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: Reading a Burette Table<\/h2>\n<p>Work out the titres from a new set of burette readings, choose the concordant ones and find the mean.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-1005\" class=\"h5p-iframe\" data-content-id=\"1005\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Standard Solution Fill In: Reading a Burette Table\"><\/iframe><\/div><\/div>\n<\/section>\n<article class=\"ols-note-card\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">8<\/div>\n<h2>Worked Calculation Ladder<\/h2>\n<\/div>\n<p>The mass of sulfamic acid is 2.41 g and the mean titre is 20.05 cm\u00b3. Every step is shown with its unit, and the unrounded value is carried from step to step.<\/p>\n<p>The final answer is given to 3 significant figures because the mass (2.41 g) and the titres (20.05 cm\u00b3, 25.0 cm\u00b3) are known to 3 significant figures.<\/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 sulfamic acid made<\/strong><\/td><td>n = m \u00f7 Mr = 2.41 \u00f7 97.1<\/td><td>0.02482 mol<\/td><\/tr>\n<tr><td><strong>2 Concentration of the acid<\/strong><\/td><td>c = n \u00f7 V = 0.02482 \u00f7 0.2500 dm\u00b3<\/td><td>0.0993 mol dm\u207b\u00b3<\/td><\/tr>\n<tr><td><strong>3 Moles of acid in the mean titre<\/strong><\/td><td>n = c \u00d7 V = 0.0993 \u00d7 0.02005 dm\u00b3<\/td><td>0.001991 mol<\/td><\/tr>\n<tr><td><strong>4 Mole ratio<\/strong><\/td><td>H\u2082NSO\u2083H(aq) + NaOH(aq) \u2192 H\u2082NSO\u2083Na(aq) + H\u2082O(l), so the ratio is 1 : 1 and n(NaOH) = n(acid)<\/td><td>0.001991 mol<\/td><\/tr>\n<tr><td><strong>5 Concentration of the alkali<\/strong><\/td><td>c = n \u00f7 V = 0.001991 \u00f7 0.0250 dm\u00b3<\/td><td>0.0796 mol dm\u207b\u00b3 (3 s.f.)<\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<p>Two checks on the answer. First, the units: mol \u00f7 dm\u00b3 gives mol dm\u207b\u00b3 at steps 2 and 5, and mol dm\u207b\u00b3 \u00d7 dm\u00b3 gives mol at step 3.<\/p><p>Second, the sense: the titre (20.05 cm\u00b3) is a little less than the pipette volume (25.0 cm\u00b3), so for a 1 : 1 reaction the alkali must be a little less concentrated than the acid, and 0.0796 is indeed a little less than 0.0993.<\/p><div class=\"ols-key-box\"><p><strong>Common mistake:<\/strong> A student who gets 79.6 or 0.000796 mol dm\u207b\u00b3 has slipped a factor of 1000 by leaving a volume in cm\u00b3.<\/p><\/div>\n<div class=\"ols-key-box\">\n<p><strong>Exam wording:<\/strong> Write the mole ratio as a line of working with the equation beside it: &#8220;H\u2082NSO\u2083H : NaOH = 1 : 1, so n(NaOH) = 0.00199 mol&#8221;. Asserting the ratio without the equation loses the reasoning mark.<\/p>\n<\/div>\n<\/article>\n<article class=\"ols-note-card purple\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">9<\/div>\n<h2>Other Primary Standards<\/h2>\n<\/div>\n<p>Sulfamic acid is one of several solids that qualify as primary standards, and a question may swap it for another; the technique is identical and only the Mr and the mole ratio change.<\/p><p><strong>Anhydrous sodium carbonate<\/strong>, Na\u2082CO\u2083, Mr 106.0, is dried in an oven and cooled in a desiccator before weighing.<\/p><p>It is a base, so it is titrated against an acid such as hydrochloric acid, with methyl orange going from yellow to orange as the acid is added:<\/p>\n<p>Na\u2082CO\u2083(aq) + 2HCl(aq) \u2192 2NaCl(aq) + H\u2082O(l) + CO\u2082(g)<\/p>\n<p>The ratio is 1 : 2, so the moles of acid in the titre are twice the moles of carbonate in the pipetted portion. Students lose marks by forgetting the factor of 2 and by writing NaCO\u2083 for the salt.<\/p>\n<p><strong>Potassium hydrogenphthalate<\/strong>, KHC\u2088H\u2084O\u2084, Mr 204.2, is a monoprotic acid with a high Mr, so a weighing of about 5 g gives a small percentage uncertainty.<\/p>\n<p>It is used to standardise sodium hydroxide exactly as sulfamic acid is, with phenolphthalein (colourless to the first permanent pale pink when the alkali is in the burette):<\/p>\n<p>KHC\u2088H\u2084O\u2084(aq) + NaOH(aq) \u2192 KNaC\u2088H\u2084O\u2084(aq) + H\u2082O(l)<\/p>\n<div class=\"ols-table-wrap\">\n<table class=\"ols-table\">\n<thead>\n<tr><th>Primary standard<\/th><th>Formula and Mr<\/th><th>Titrated against<\/th><th>Ratio<\/th><\/tr>\n<\/thead>\n<tbody>\n<tr><td><strong>Sulfamic acid<\/strong><\/td><td>H\u2082NSO\u2083H, 97.1<\/td><td>Sodium hydroxide<\/td><td>1 : 1<\/td><\/tr>\n<tr><td><strong>Anhydrous sodium carbonate<\/strong><\/td><td>Na\u2082CO\u2083, 106.0<\/td><td>Hydrochloric acid<\/td><td>1 : 2 (carbonate : acid)<\/td><\/tr>\n<tr><td><strong>Potassium hydrogenphthalate<\/strong><\/td><td>KHC\u2088H\u2084O\u2084, 204.2<\/td><td>Sodium hydroxide<\/td><td>1 : 1<\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<div class=\"ols-key-box\">\n<p><strong>Key idea:<\/strong> Whichever solid is used, the ladder is the same five steps. Read the equation for the ratio before step 4, and check whether the standard is the acid or the base so that you know which solution is in the burette.<\/p>\n<\/div>\n<\/article>\n<article class=\"ols-note-card soft\">\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>The <strong>percentage uncertainty<\/strong> of a measurement is (uncertainty \u00f7 reading) \u00d7 100. A mass by difference and a titre each come from two readings, so their uncertainties are doubled before dividing. Using the sample data:<\/p>\n<div class=\"ols-table-wrap\">\n<table class=\"ols-table\">\n<thead>\n<tr><th>Measurement<\/th><th>Uncertainty<\/th><th>Working<\/th><th>Percentage uncertainty<\/th><\/tr>\n<\/thead>\n<tbody>\n<tr><td><strong>Mass of acid, 2.41 g<\/strong><\/td><td>2 \u00d7 \u00b10.005 g = \u00b10.01 g<\/td><td>0.01 \u00f7 2.41 \u00d7 100<\/td><td>0.41 %<\/td><\/tr>\n<tr><td><strong>Titre, 20.05 cm\u00b3<\/strong><\/td><td>2 \u00d7 \u00b10.05 cm\u00b3 = \u00b10.10 cm\u00b3<\/td><td>0.10 \u00f7 20.05 \u00d7 100<\/td><td>0.50 %<\/td><\/tr>\n<tr><td><strong>Pipette, 25.0 cm\u00b3<\/strong><\/td><td>\u00b10.06 cm\u00b3<\/td><td>0.06 \u00f7 25.0 \u00d7 100<\/td><td>0.24 %<\/td><\/tr>\n<tr><td><strong>Volumetric flask, 250.0 cm\u00b3<\/strong><\/td><td>\u00b10.15 cm\u00b3 (class A)<\/td><td>0.15 \u00f7 250.0 \u00d7 100<\/td><td>0.06 % (0.12 % for a class B flask, \u00b10.30 cm\u00b3)<\/td><\/tr>\n<tr><td><strong>Total<\/strong><\/td><td>Add the percentages<\/td><td>0.41 + 0.50 + 0.24 + 0.06<\/td><td>about 1.2 %<\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<p>The burette contributes most, so the improvement that pays is a <strong>larger titre<\/strong>: a 50 cm\u00b3 pipette of alkali, or a slightly less concentrated acid, roughly halves the burette percentage.<\/p><p>Weighing more solid would reduce the balance term, but 2.4 g already gives under half a percent. The flask and pipette are so precise that swapping them changes little.<\/p><p>Percentage uncertainties are measurement limits, and they are different from the technique errors below, which push the answer in one direction.<\/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 calculated alkali concentration<\/th><th>Improvement<\/th><\/tr>\n<\/thead>\n<tbody>\n<tr><td><strong>Washings not added to the flask<\/strong><\/td><td>Too high: fewer moles of acid in the flask than calculated, so the acid is weaker and the titre larger<\/td><td>Rinse beaker, rod and funnel and add every rinsing<\/td><\/tr>\n<tr><td><strong>Flask filled above the mark<\/strong><\/td><td>Too high: acid diluted but 250.0 cm\u00b3 still used in the calculation<\/td><td>Finish with a dropping pipette at eye level; start again if overshot<\/td><\/tr>\n<tr><td><strong>Warm solution made up to the mark<\/strong><\/td><td>Too low: the solution contracts, the volume is below 250 cm\u00b3, the acid is stronger than calculated and the titre smaller<\/td><td>Cool to room temperature before transferring<\/td><\/tr>\n<tr><td><strong>Air bubble in the burette jet<\/strong><\/td><td>Too high: the bubble counts as acid delivered so the titre reads too large<\/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>Too low: a drip after the initial reading makes the final reading lower, so the titre is too small<\/td><td>Remove the funnel before every reading<\/td><\/tr>\n<tr><td><strong>Pipette rinsed with water only<\/strong><\/td><td>Too low: the alkali is diluted so fewer moles are in the flask and the titre is smaller<\/td><td>Rinse the pipette with the alkali<\/td><\/tr>\n<tr><td><strong>Burette rinsed with water only<\/strong><\/td><td>Too high: the acid is diluted so a larger titre is needed<\/td><td>Rinse the burette with the acid<\/td><\/tr>\n<tr><td><strong>End point overshot to red<\/strong><\/td><td>Too high: titre too large<\/td><td>Add dropwise near the end point and stop at the first permanent orange<\/td><\/tr>\n<tr><td><strong>Burette read from the top of the meniscus<\/strong><\/td><td>Small and random: both readings shift together, but inconsistent reading gives scattered titres<\/td><td>Read the bottom of the meniscus at eye level every time<\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<div class=\"ols-key-box\">\n<p><strong>Exam wording:<\/strong> &#8220;The percentage uncertainty in the titre is 0.10 \u00f7 20.05 \u00d7 100 = 0.50 %. Using a larger volume of alkali would give a larger titre and reduce this.&#8221; State the uncertainty, the working and the improvement that reduces it.<\/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 Diprotic Standard<\/h2>\n<p>Run a full titration calculation for ethanedioic acid dihydrate, including a 1 : 2 ratio and the titre uncertainty.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-1006\" class=\"h5p-iframe\" data-content-id=\"1006\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Standard Solution Quick Choice: Ethanedioic Acid Calculation\"><\/iframe><\/div><\/div>\n<\/section>\n<article class=\"ols-note-card\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">11<\/div>\n<h2>Common Mistakes<\/h2>\n<\/div>\n<ul>\n<li><strong>Leaving a volume in cm\u00b3<\/strong>: divide by 1000 before using c = n \u00f7 V; an answer of 79.6 mol dm\u207b\u00b3 for a dilute alkali should ring alarm bells.<\/li>\n<li><strong>Averaging every titre<\/strong>, including the rough one, or treating only identical titres as concordant.<\/li>\n<li><strong>Rounding too early<\/strong>: 0.0248 \u00f7 0.250 gives 0.0992, while the unrounded 0.02482 gives 0.0993. Carry an extra figure and round once at the end to 3 s.f.<\/li>\n<li><strong>Weighing the empty bottle first<\/strong> and assuming every grain was transferred; weigh the bottle with the acid, then with the residue.<\/li>\n<li><strong>Reading the top of the meniscus<\/strong>, leaving the funnel in the burette, or starting with an air bubble in the jet.<\/li>\n<li><strong>Not swirling<\/strong>, so the end point appears early in one part of the flask, or going on past orange to red.<\/li>\n<li><strong>Too much indicator<\/strong>: 2 to 3 drops, because the indicator is itself a weak acid that reacts with some of the alkali.<\/li>\n<li><strong>Drying the conical flask<\/strong> &#8220;for accuracy&#8221;: water in the flask changes nothing, since the moles of alkali were fixed by the pipette.<\/li>\n<li><strong>Asserting the 1 : 1 ratio<\/strong> without writing the equation, or applying 1 : 1 to a diprotic acid or a carbonate.<\/li>\n<li><strong>Quoting 0.079612 mol dm\u207b\u00b3<\/strong>: five or six significant figures cannot be justified by 3 s.f. data.<\/li>\n<\/ul>\n<\/article>\n<section class=\"ols-h5p-card ols-h5p-inline\">\n<span class=\"ols-h5p-kicker\">Check your understanding<\/span>\n<h2>Check: What Each Slip Does<\/h2>\n<p>In each round, choose the statement that correctly describes the effect of a slip in making or using a standard solution.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-1072\" class=\"h5p-iframe\" data-content-id=\"1072\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Standard Solution Summary: What Each Slip Does to the Result\"><\/iframe><\/div><\/div>\n<\/section>\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;Weigh the bottle with the acid, tip it out, reweigh the bottle with any residue: mass used = m\u2081 \u2212 m\u2082.&#8221;<\/p><p>&#8220;Rinse the beaker, rod and funnel and add the washings so that all of the acid reaches the flask.&#8221;<\/p><p>&#8220;Bottom of the meniscus on the line at eye level.&#8221; &#8220;Methyl orange turns from yellow to orange.&#8221;<\/p><p>&#8220;Titres concordant within 0.10 cm\u00b3 of each other; mean to 2 d.p.; answer to 3 s.f.&#8221;<\/p>\n<h3>Do not say<\/h3><p>&#8220;Fill the flask up&#8221; (make up to the mark). &#8220;Concordant means the same&#8221; (within the stated limit). &#8220;Heating the flask expands the glass&#8221; (the liquid contracts on cooling). &#8220;Dry the conical flask&#8221; (water there does not matter). &#8220;Sulfamic acid : NaOH is 1 : 1&#8221; without the equation.<\/p>\n<h3>Watch for<\/h3><p>Calculation questions that swap the primary standard for a carbonate or a diprotic acid: read the equation for the ratio.<\/p><p>Uncertainty questions: two readings for a mass by difference and for a titre, so double the instrument uncertainty before dividing.<\/p><p>Evaluation questions: say whether the alkali concentration comes out too high or too low, and why.<\/p><p>Related technique on <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/practical-activity-groups\/pag-2-acid-base-titration\/\">PAG 2 (concentration of hcl by titration)<\/a> and, for the same volumetric glassware used in gas work, <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/practical-activity-groups\/pag-1-molar-volume-of-a-gas\/\">PAG 1 (molar volume of a gas)<\/a>.<\/p>\n<\/article>\n<section class=\"ols-faq-card\">\n<h2>FAQs<\/h2>\n<p>Short answers to the questions OCR A examiners ask most often about PAG 2.<\/p>\n\n<div class=\"ols-faq-list\">\n<div class=\"ols-faq-item\">\n<h3>Why is sulfamic acid used as the primary standard and not sodium hydroxide?<\/h3>\n<p>Sulfamic acid is a pure, stable crystalline solid that does not absorb water or carbon dioxide from the air and has a reasonably high Mr (97.1), so a weighed mass gives its moles directly.<\/p><p>Sodium hydroxide pellets absorb water and carbon dioxide while they are being weighed, so their mass never gives an accurate number of moles; its concentration has to be found by titration against a primary standard.<\/p>\n<\/div>\n\n<div class=\"ols-faq-item\">\n<h3>Why is a volumetric flask used instead of a measuring cylinder?<\/h3>\n<p>A 250 cm\u00b3 volumetric flask is calibrated to contain exactly 250.0 cm\u00b3 at 20 \u00b0C when the bottom of the meniscus sits on its single line, with an uncertainty of only \u00b10.15 cm\u00b3 (class A).<\/p><p>A measuring cylinder of the same size has an uncertainty of \u00b11 cm\u00b3 or more, and its wide bore makes the meniscus hard to place.<\/p>\n<\/div>\n\n<div class=\"ols-faq-item\">\n<h3>Why is the burette rinsed with the acid and the pipette with the alkali?<\/h3>\n<p>Any water left inside would dilute the solution before its volume is measured.<\/p><p>A diluted acid in the burette gives a titre that is too large; a diluted alkali in the pipette puts fewer moles into the flask and gives a titre that is too small.<\/p><p>Rinsing each with the solution it will hold removes the problem.<\/p>\n<\/div>\n\n<div class=\"ols-faq-item\">\n<h3>What colour change is seen, and when do you stop?<\/h3>\n<p>Methyl orange is yellow in the sodium hydroxide and red in acid.<\/p><p>As sulfamic acid is added from the burette the flask stays yellow, flickers orange with swirling near the end point, and the titration stops at the first permanent orange colour.<\/p><p>Red means the end point has been overshot and the titre is too large.<\/p>\n<\/div>\n\n<div class=\"ols-faq-item\">\n<h3>Why is the rough titre not used in the mean?<\/h3>\n<p>The rough titre is run quickly to find roughly where the end point is, so the acid is added in large portions and the end point is usually overshot.<\/p>\n<p>It is not an accurate measurement and it is excluded even if it happens to fall close to the accurate titres. Only concordant accurate titres are averaged.<\/p>\n<\/div>\n\n<div class=\"ols-faq-item\">\n<h3>Why does water in the conical flask not matter, when water in the pipette does?<\/h3>\n<p>The moles of sodium hydroxide are fixed when 25.0 cm\u00b3 is pipetted into the flask; adding water afterwards dilutes them but does not change their number, so the titre is unchanged. Water in the pipette dilutes the alkali before it is measured, so 25.0 cm\u00b3 then contains fewer moles.<\/p>\n<\/div>\n\n<div class=\"ols-faq-item\">\n<h3>What happens to the answer if the volumetric flask is filled above the mark?<\/h3>\n<p>The acid is more dilute than the calculation assumes, because the student still uses 250.0 cm\u00b3. A larger titre is needed to neutralise the 25.0 cm\u00b3 of alkali, and the calculated alkali concentration comes out too high. The only remedy is to start the preparation again.<\/p>\n<\/div>\n<\/div>\n<\/section>\n<section class=\"ols-related-card\">\n<h2>Related Practical Activity Groups 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\/ocr-a\/practical-activity-groups\/pag-1-molar-volume-of-a-gas\/\">PAG 1: Molar Volume of a Gas<\/a>\n<a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/practical-activity-groups\/pag-3-enthalpy-determination\/\">PAG 3: 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\/ocr-a\/practical-activity-groups\/pag-2-acid-base-titration\/\">PAG 2: Concentration of HCl by Titration<\/a>\n<a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/practical-activity-groups\/rates-of-hydrolysis-of-haloalkanes\/\">Hydrolysis rates: Hydrolysis of Halogenoalkanes<\/a>\n<a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/practical-activity-groups\/pag-5-synthesis-of-an-organic-liquid\/\">PAG 5: Chlorination of 2-methylpropan-2-ol<\/a>\n<a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/practical-activity-groups\/pag-5-oxidation-of-an-alcohol\/\">PAG 5: Oxidation of an Alcohol<\/a>\n<a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/practical-activity-groups\/pag-4-pag-7-qualitative-analysis-of-ions-and-functional-groups\/\">PAG 4 and 7: Analysis of Inorganic and Organic Unknowns<\/a>\n<a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/practical-activity-groups\/\">Practical Activity Groups (PAGs) 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          var closeButton = lightbox.querySelector(\".ols-image-lightbox-close\");\n          var clickableImages = page.querySelectorAll(\"img.ols-lightbox-target\");\n          function openLightbox(image) {\n            lightboxImage.src = image.currentSrc || image.src;\n            lightboxImage.alt = image.alt || \"Expanded revision image\";\n            lightbox.classList.add(\"is-open\");\n            lightbox.setAttribute(\"aria-hidden\", \"false\");\n            if (!document.body.dataset.olsPreviousOverflow) {\n              document.body.dataset.olsPreviousOverflow = document.body.style.overflow || \"default\";\n            }\n            document.body.style.overflow = \"hidden\";\n          }\n          function closeLightbox() {\n            lightbox.classList.remove(\"is-open\");\n            lightbox.setAttribute(\"aria-hidden\", \"true\");\n            lightboxImage.src = \"\";\n            if (document.body.dataset.olsPreviousOverflow) {\n              document.body.style.overflow = document.body.dataset.olsPreviousOverflow === \"default\" ? \"\" : document.body.dataset.olsPreviousOverflow;\n              delete document.body.dataset.olsPreviousOverflow;\n            }\n          }\n          clickableImages.forEach(function(image){\n            image.addEventListener(\"click\", function(event){\n              event.preventDefault();\n              event.stopPropagation();\n              openLightbox(image);\n            });\n          });\n          closeButton.addEventListener(\"click\", closeLightbox);\n          lightbox.addEventListener(\"click\", function(event){ if (event.target === lightbox) { closeLightbox(); } });\n          document.addEventListener(\"keydown\", function(event){ if (event.key === \"Escape\" && lightbox.classList.contains(\"is-open\")) { closeLightbox(); } });\n        })();\n      <\/script>\n\n      <script type=\"application\/ld+json\">\n{\n  \"@context\": \"https:\/\/schema.org\",\n  \"@graph\": [\n    {\n      \"@type\": \"WebPage\",\n      \"@id\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/practical-activity-groups\/pag-2-preparing-a-standard-solution\/#webpage\",\n      \"url\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/practical-activity-groups\/pag-2-preparing-a-standard-solution\/\",\n      \"name\": \"PAG 2 Preparing a Standard Solution | Practical Activity Groups | Online Learning System\",\n      \"description\": \"OCR A A Level Chemistry revision notes on PAG 2: preparing a standard solution of sulfamic acid and using it to find the concentration of sodium hydroxide by titration, with method, sample data, calculation, uncertainty and common errors.\",\n      \"isPartOf\": {\n        \"@id\": \"https:\/\/www.onlinelearningsystem.net\/#website\"\n      },\n      \"breadcrumb\": {\n        \"@id\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/practical-activity-groups\/pag-2-preparing-a-standard-solution\/#breadcrumb\"\n      }\n    },\n    {\n      \"@type\": \"WebSite\",\n      \"@id\": \"https:\/\/www.onlinelearningsystem.net\/#website\",\n      \"url\": \"https:\/\/www.onlinelearningsystem.net\/\",\n      \"name\": \"Online Learning System\"\n    },\n    {\n      \"@type\": \"BreadcrumbList\",\n      \"@id\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/practical-activity-groups\/pag-2-preparing-a-standard-solution\/#breadcrumb\",\n      \"itemListElement\": [\n        {\n          \"@type\": \"ListItem\",\n          \"position\": 1,\n          \"item\": {\n            \"@type\": \"WebPage\",\n            \"@id\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/\",\n            \"url\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/\",\n            \"name\": \"Revision Notes\"\n          }\n        },\n        {\n          \"@type\": \"ListItem\",\n          \"position\": 2,\n          \"item\": {\n            \"@type\": \"WebPage\",\n            \"@id\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/\",\n            \"url\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/\",\n            \"name\": \"A Level Chemistry\"\n          }\n        },\n        {\n          \"@type\": \"ListItem\",\n          \"position\": 3,\n          \"item\": {\n            \"@type\": \"WebPage\",\n            \"@id\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/\",\n            \"url\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/\",\n            \"name\": \"OCR A\"\n          }\n        },\n        {\n          \"@type\": \"ListItem\",\n          \"position\": 4,\n          \"item\": {\n            \"@type\": \"WebPage\",\n            \"@id\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/practical-activity-groups\/\",\n            \"url\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/practical-activity-groups\/\",\n            \"name\": \"Practical Activity Groups (PAGs)\"\n          }\n        },\n        {\n          \"@type\": \"ListItem\",\n          \"position\": 5,\n          \"item\": {\n            \"@type\": \"WebPage\",\n            \"@id\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/practical-activity-groups\/pag-2-preparing-a-standard-solution\/\",\n            \"url\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/practical-activity-groups\/pag-2-preparing-a-standard-solution\/\",\n            \"name\": \"PAG 2 Preparing a Standard Solution\"\n          }\n        }\n      ]\n    },\n    {\n      \"@type\": \"Course\",\n      \"@id\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/practical-activity-groups\/pag-2-preparing-a-standard-solution\/#course\",\n      \"name\": \"PAG 2 Preparing a Standard Solution\",\n      \"description\": \"OCR A A Level Chemistry revision notes on PAG 2: preparing a standard solution of sulfamic acid and using it to find the concentration of sodium hydroxide by titration, with method, sample data, calculation, uncertainty and common errors.\",\n      \"provider\": {\n        \"@type\": \"Organization\",\n        \"name\": \"Online Learning System\",\n        \"url\": \"https:\/\/www.onlinelearningsystem.net\/\"\n      },\n      \"educationalLevel\": \"A Level\",\n      \"about\": [\n        \"Practical chemistry\",\n        \"Preparation of a Standard Solution\"\n      ],\n      \"hasCourseInstance\": {\n        \"@type\": \"CourseInstance\",\n        \"courseMode\": \"Online\"\n      }\n    },\n    {\n      \"@type\": \"ItemList\",\n      \"@id\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/practical-activity-groups\/pag-2-preparing-a-standard-solution\/#relatedtopics\",\n      \"name\": \"Related Practical Activity Groups Pages\",\n      \"itemListElement\": [\n        {\n          \"@type\": \"ListItem\",\n          \"position\": 1,\n          \"item\": {\n            \"@type\": \"Course\",\n            \"name\": \"PAG 1 Moles Determination: Molar Volume of a Gas\",\n            \"url\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/practical-activity-groups\/pag-1-molar-volume-of-a-gas\/\",\n            \"description\": \"OCR A A Level Chemistry revision notes on measuring the molar volume of a gas: collecting CO\u2082 over water, the graph of volume against mass, the calculation to 24 dm\u00b3 mol\u207b\u00b9, percentage uncertainty and the errors examiners ask about.\"\n          }\n        },\n        {\n          \"@type\": \"ListItem\",\n          \"position\": 2,\n          \"item\": {\n            \"@type\": \"Course\",\n            \"name\": \"PAG 3 Enthalpy Determination: Hess's Law\",\n            \"url\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/practical-activity-groups\/pag-3-enthalpy-determination\/\",\n            \"description\": \"OCR A A Level Chemistry revision notes on PAG 3: enthalpy change via Hess's law from K\u2082CO\u2083 and KHCO\u2083 with HCl, with q = mc\u0394T, the Hess cycle, percentage uncertainty and error analysis.\"\n          }\n        },\n        {\n          \"@type\": \"ListItem\",\n          \"position\": 3,\n          \"item\": {\n            \"@type\": \"Course\",\n            \"name\": \"PAG 2 Acid\u2013Base Titration\",\n            \"url\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/practical-activity-groups\/pag-2-acid-base-titration\/\",\n            \"description\": \"OCR A A Level Chemistry revision notes on PAG 2: finding the concentration of hydrochloric acid by titration with standardised sodium hydroxide, with method reasons, concordant titres, the worked calculation, error directions and percentage uncertainty.\"\n          }\n        },\n        {\n          \"@type\": \"ListItem\",\n          \"position\": 4,\n          \"item\": {\n            \"@type\": \"Course\",\n            \"name\": \"Comparing the Rates of Hydrolysis of Haloalkanes\",\n            \"url\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/practical-activity-groups\/rates-of-hydrolysis-of-haloalkanes\/\",\n            \"description\": \"OCR A A Level Chemistry revision notes on Practical Skills: Rates of Hydrolysis: comparing the rates of hydrolysis of haloalkanes with aqueous silver nitrate in ethanol at 50 \u00b0C, the role of each reagent, silver halide colours, 1\/t, bond enthalpies and carbocation stability, with errors, improvements and exam points.\"\n          }\n        },\n        {\n          \"@type\": \"ListItem\",\n          \"position\": 5,\n          \"item\": {\n            \"@type\": \"Course\",\n            \"name\": \"PAG 5 Synthesis of an Organic Liquid: 2-chloro-2-methylpropane\",\n            \"url\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/practical-activity-groups\/pag-5-synthesis-of-an-organic-liquid\/\",\n            \"description\": \"OCR A A Level Chemistry revision notes on the chlorination of 2-methylpropan-2-ol (PAG 5): S\u20991 mechanism via the tertiary carbocation, separating funnel technique, hydrogencarbonate wash, drying, simple distillation at 50\u201352 \u00b0C, silver nitrate test with nitric acid, worked percentage yield and evaluation.\"\n          }\n        },\n        {\n          \"@type\": \"ListItem\",\n          \"position\": 6,\n          \"item\": {\n            \"@type\": \"Course\",\n            \"name\": \"PAG 5 Oxidation of an Alcohol: Distil or Reflux\",\n            \"url\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/practical-activity-groups\/pag-5-oxidation-of-an-alcohol\/\",\n            \"description\": \"OCR A A Level Chemistry revision notes on PAG 5: oxidation of ethanol to ethanal by distillation and to ethanoic acid by reflux, with apparatus, boiling points, equations, product tests and exam points.\"\n          }\n        },\n        {\n          \"@type\": \"ListItem\",\n          \"position\": 7,\n          \"item\": {\n            \"@type\": \"Course\",\n            \"name\": \"PAG 4 and PAG 7 Qualitative Analysis of Unknowns\",\n            \"url\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/practical-activity-groups\/pag-4-pag-7-qualitative-analysis-of-ions-and-functional-groups\/\",\n            \"description\": \"OCR A A Level Chemistry revision notes on PAG 4 and PAG 7: identifying unknown organic liquids and inorganic solids by test-tube reactions, with the method, safety, ionic equations with state symbols, the evidence trail, exam data practice and interactive checks.\"\n          }\n        }\n      ]\n    }\n  ]\n}\n<\/script>\n    <\/main>\n<\/section>\n","protected":false},"excerpt":{"rendered":"<p>Revision Notes \/ A Level Chemistry \/ OCR A \/ Practical Activity Groups (PAGs) \/ PAG 2 Preparing a Standard Solution PAG 2 Preparing a Standard Solution PAG 2 for OCR A A Level Chemistry: prepare a standard solution of sulfamic acid, H\u2082NSO\u2083H, by weighing by difference and making up to 250.0 cm\u00b3, then titrate [&hellip;]<\/p>\n","protected":false},"author":12,"featured_media":0,"parent":11286,"menu_order":3,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-11290","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/pages\/11290","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=11290"}],"version-history":[{"count":0,"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/pages\/11290\/revisions"}],"up":[{"embeddable":true,"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/pages\/11286"}],"wp:attachment":[{"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/media?parent=11290"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}