{"id":4506,"date":"2026-05-28T05:25:07","date_gmt":"2026-05-28T04:25:07","guid":{"rendered":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/cp-3-concentration-of-hcl-by-titration\/"},"modified":"2026-06-10T08:29:08","modified_gmt":"2026-06-10T07:29:08","slug":"cp-3-concentration-of-hcl-by-titration","status":"publish","type":"page","link":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/core-practicals\/cp-3-concentration-of-hcl-by-titration\/","title":{"rendered":"CP 3 &#8211; Concentration of HCl by Titration"},"content":{"rendered":"\n<section class=\"ols-revision-page ols-cp3-page\" id=\"ols-cp3-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      --green: #3f8f46;\n      --orange: #f97316;\n      --red: #d94b2b;\n      --gold: #c9973a;\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\n    .ols-revision-layout {\n      display: grid;\n      grid-template-columns: 310px minmax(0, 1fr);\n      gap: 34px;\n      max-width: 1450px;\n      margin: 0 auto;\n      padding: 24px 20px 60px;\n    }\n\n    .ols-sidebar {\n      position: sticky;\n      top: 20px;\n      align-self: start;\n      background: #ffffff;\n      border: 1px solid var(--border);\n      border-radius: 24px;\n      box-shadow: var(--shadow);\n      overflow: hidden;\n    }\n\n    .ols-sidebar-header {\n      padding: 22px;\n      border-bottom: 1px solid var(--border);\n      background: linear-gradient(135deg, #ffffff, var(--soft-blue));\n    }\n\n    .ols-sidebar-header h3 {\n      margin: 0 0 6px;\n      font-size: 21px;\n      font-weight: 700;\n      color: var(--navy);\n    }\n\n    .ols-sidebar-header p {\n      margin: 0;\n      font-size: 14px;\n      color: var(--grey-text);\n      line-height: 1.5;\n    }\n\n    .ols-topic-group {\n      padding: 18px 22px;\n      border-bottom: 1px solid var(--border);\n    }\n\n    .ols-topic-group:last-child { border-bottom: none; }\n\n    .ols-topic-group h4 {\n      margin: 0 0 14px;\n      font-size: 17px;\n      font-weight: 700;\n      color: var(--navy);\n    }\n\n    .ols-topic-list {\n      list-style: none;\n      margin: 0;\n      padding: 0;\n      display: grid;\n      gap: 8px;\n    }\n\n    .ols-topic-list li {\n      border-radius: 14px;\n      font-size: 15px;\n      line-height: 1.35;\n      color: #344054;\n      background: transparent;\n    }\n\n    .ols-topic-list li.active {\n      padding: 11px 12px;\n      background: var(--soft-blue);\n      color: var(--blue);\n      font-weight: 700;\n    }\n\n    .ols-topic-list li:not(.active) { padding: 0; }\n\n    .ols-topic-list a {\n      display: block;\n      padding: 11px 12px;\n      border-radius: 14px;\n      color: #344054;\n      text-decoration: none;\n      transition: background 0.2s ease, color 0.2s ease;\n    }\n\n    .ols-topic-list a:hover {\n      background: var(--soft-blue);\n      color: var(--blue);\n    }\n\n    .ols-main {\n      min-width: 0;\n      max-width: 970px;\n    }\n\n    .ols-breadcrumbs {\n      display: flex;\n      flex-wrap: wrap;\n      gap: 8px;\n      margin: 10px 0 22px;\n      font-size: 15px;\n      color: var(--grey-text);\n    }\n\n    .ols-breadcrumbs a,\n    .ols-breadcrumbs span {\n      color: var(--grey-text);\n      text-decoration: none;\n      font-weight: 600;\n    }\n\n    .ols-breadcrumbs a:hover {\n      color: var(--blue);\n      text-decoration: underline;\n      text-underline-offset: 3px;\n    }\n\n    .ols-title-card,\n    .ols-note-card,\n    .ols-related-card {\n      background: #ffffff;\n      border: 1px solid var(--border);\n      border-radius: 28px;\n      box-shadow: var(--shadow);\n      padding: 34px;\n      margin-bottom: 24px;\n      overflow: visible;\n    }\n\n    .ols-title-card {\n      background: linear-gradient(135deg, #ffffff 0%, #f8fbff 100%);\n    }\n\n    .ols-title-card h1 {\n      margin: 0 0 18px;\n      font-size: clamp(34px, 5vw, 56px);\n      line-height: 1.08;\n      font-weight: 800;\n      letter-spacing: -0.04em;\n      color: #111827;\n    }\n\n    .ols-page-intro {\n      font-size: 19px;\n      line-height: 1.7;\n      font-weight: 300;\n      color: var(--body-text);\n      margin: 0 0 22px;\n    }\n\n    .ols-badges {\n      display: flex;\n      flex-wrap: wrap;\n      gap: 12px;\n      margin-bottom: 22px;\n    }\n\n    .ols-badge {\n      display: inline-flex;\n      align-items: center;\n      padding: 9px 14px;\n      border-radius: 999px;\n      background: #ffffff;\n      border: 1px solid var(--border);\n      font-size: 15px;\n      font-weight: 600;\n      color: var(--navy);\n    }\n\n    .ols-author {\n      display: flex;\n      align-items: center;\n      gap: 20px;\n      padding: 28px;\n      border-radius: 28px;\n      background: linear-gradient(135deg, #ffffff 0%, #f8fbff 100%);\n      border: 1px solid rgba(28, 36, 75, 0.12);\n      box-shadow: 0 18px 45px rgba(28, 36, 75, 0.10);\n      margin-top: 22px;\n    }\n\n    .ols-author-avatar-img {\n      width: 92px;\n      height: 92px;\n      border-radius: 50%;\n      object-fit: cover;\n      object-position: center;\n      flex-shrink: 0;\n      border: 4px solid #ffffff;\n      box-shadow:\n        0 14px 32px rgba(28, 36, 75, 0.18),\n        0 0 0 1px rgba(28, 36, 75, 0.10);\n      transition:\n        transform 0.25s ease,\n        box-shadow 0.25s ease;\n    }\n\n    .ols-author:hover .ols-author-avatar-img {\n      transform: scale(1.04);\n      box-shadow:\n        0 20px 42px rgba(28, 36, 75, 0.22),\n        0 0 0 1px rgba(28, 36, 75, 0.10);\n    }\n\n    .ols-author-content {\n      min-width: 0;\n    }\n\n    .ols-author-title {\n      margin: 0 0 4px;\n      font-size: clamp(24px, 3vw, 34px);\n      line-height: 1.15;\n      font-weight: 700;\n      color: var(--navy);\n      letter-spacing: -0.03em;\n    }\n\n    .ols-author-description {\n      margin: 0;\n      font-size: 17px;\n      line-height: 1.7;\n      font-weight: 300;\n      color: var(--grey-text);\n    }\n\n    .ols-linkedin-pill {\n      display: inline-flex;\n      align-items: center;\n      justify-content: center;\n      gap: 10px;\n      margin-top: 16px;\n      padding: 11px 18px;\n      border-radius: 999px;\n      background: linear-gradient(135deg, #0A66C2, #004182);\n      color: #ffffff;\n      text-decoration: none;\n      font-size: 14px;\n      line-height: 1;\n      font-weight: 700;\n      letter-spacing: 0.01em;\n      box-shadow: 0 10px 22px rgba(10, 102, 194, 0.24);\n      position: relative;\n      overflow: hidden;\n      transition:\n        transform 0.22s ease,\n        box-shadow 0.22s ease;\n    }\n\n    .ols-linkedin-pill::before {\n      content: \"\";\n      position: absolute;\n      top: 0;\n      left: -120%;\n      width: 100%;\n      height: 100%;\n      background: linear-gradient(\n        120deg,\n        rgba(255,255,255,0) 0%,\n        rgba(255,255,255,0.28) 50%,\n        rgba(255,255,255,0) 100%\n      );\n      transition: left 0.7s ease;\n    }\n\n    .ols-linkedin-pill:hover {\n      transform: translateY(-3px) scale(1.03);\n      box-shadow:\n        0 16px 34px rgba(10, 102, 194, 0.34),\n        0 0 0 6px rgba(10, 102, 194, 0.10);\n      color: #ffffff;\n    }\n\n    .ols-linkedin-pill:hover::before {\n      left: 120%;\n    }\n\n    .ols-linkedin-icon {\n      width: 18px;\n      height: 18px;\n      display: block;\n      flex-shrink: 0;\n    }\n\n    .ols-note-card.soft {\n      background: linear-gradient(135deg, #ffffff 0%, var(--soft-red) 100%);\n    }\n\n    .ols-note-card.purple {\n      background: linear-gradient(135deg, #ffffff 0%, var(--soft-purple) 100%);\n    }\n\n    .ols-note-title {\n      display: flex;\n      align-items: center;\n      gap: 14px;\n      margin-bottom: 20px;\n    }\n\n    .ols-note-icon {\n      width: 52px;\n      height: 52px;\n      border-radius: 16px;\n      background: var(--navy);\n      color: #ffffff;\n      display: grid;\n      place-items: center;\n      font-size: 24px;\n      font-weight: 800;\n      flex-shrink: 0;\n    }\n\n    .ols-note-title h2,\n    .ols-related-card h2 {\n      margin: 0;\n      font-size: clamp(28px, 3.5vw, 42px);\n      line-height: 1.15;\n      font-weight: 800;\n      color: #111827;\n      letter-spacing: -0.03em;\n    }\n\n    .ols-related-card h2 {\n      margin-bottom: 14px;\n    }\n\n    .ols-note-card p,\n    .ols-note-card li,\n    .ols-related-card p {\n      font-size: clamp(15px, 1.2vw, 17px);\n      line-height: 1.68;\n      font-weight: 300;\n      color: var(--body-text);\n    }\n\n    .ols-note-card strong,\n    .ols-related-card strong {\n      font-weight: 700;\n      color: var(--navy);\n    }\n\n    .ols-note-card ul,\n    .ols-note-card ol {\n      margin: 0;\n      padding-left: 22px;\n    }\n\n    .ols-key-box {\n      margin-top: 20px;\n      background: var(--soft-green);\n      border: 1px solid rgba(63, 143, 70, 0.25);\n      border-radius: 20px;\n      padding: 18px 20px;\n    }\n\n    .ols-key-box p {\n      margin: 0;\n      font-weight: 400;\n      color: var(--navy);\n    }\n\n    .ols-formula-box {\n      margin-top: 22px;\n      padding: 20px 22px;\n      border-radius: 20px;\n      background: linear-gradient(135deg, #ffffff, var(--soft-blue));\n      border: 1px solid rgba(37, 99, 235, 0.18);\n    }\n\n    .ols-formula-box p {\n      margin: 0 0 10px;\n      font-weight: 400;\n      color: var(--navy);\n    }\n\n    .ols-formula-box p:last-child { margin-bottom: 0; }\n\n    .ols-figure-card {\n      margin: 26px 0 4px;\n      border: 1px solid var(--border);\n      border-radius: 26px;\n      overflow: visible;\n      background: #ffffff;\n      box-shadow: var(--inner-shadow);\n      position: relative;\n      z-index: 1;\n    }\n\n    .ols-figure-image {\n      width: 100%;\n      min-height: 320px;\n      display: flex;\n      align-items: center;\n      justify-content: center;\n      background: #ffffff;\n      padding: 20px;\n      border-radius: 26px 26px 0 0;\n      overflow: visible;\n      position: relative;\n      cursor: zoom-in;\n    }\n\n    .ols-figure-image::after {\n      content: \"Click to enlarge\";\n      position: absolute;\n      right: 14px;\n      bottom: 14px;\n      z-index: 3;\n      padding: 8px 12px;\n      border-radius: 999px;\n      background: rgba(28, 36, 75, 0.88);\n      color: #ffffff;\n      font-size: 12px;\n      line-height: 1;\n      font-weight: 800;\n      opacity: 0;\n      transform: translateY(6px);\n      transition: opacity 0.22s ease, transform 0.22s ease;\n      pointer-events: none;\n    }\n\n    .ols-figure-image:hover::after {\n      opacity: 1;\n      transform: translateY(0);\n    }\n\n    .ols-figure-image img {\n      max-width: 100%;\n      height: auto;\n      display: block;\n      cursor: zoom-in;\n      transition: transform 0.32s ease, box-shadow 0.32s ease, filter 0.32s ease;\n      transform-origin: center center;\n      will-change: transform;\n      position: relative;\n      z-index: 2;\n    }\n\n    @media (hover: hover) and (pointer: fine) {\n      .ols-figure-card .ols-figure-image:hover img {\n        transform: scale(1.5);\n        box-shadow: 0 30px 80px rgba(28, 36, 75, 0.28);\n        filter: saturate(1.05) contrast(1.03);\n      }\n\n      .ols-figure-card:hover {\n        z-index: 50;\n      }\n    }\n\n    .ols-figure-caption {\n      padding: 22px 26px 24px;\n      background: linear-gradient(135deg, #ffffff, #f8fbff);\n    }\n\n    .ols-figure-caption h3 {\n      margin: 0 0 8px;\n      color: var(--navy);\n      font-size: clamp(21px, 2vw, 28px);\n      line-height: 1.25;\n      font-weight: 800;\n      font-style: italic;\n    }\n\n    .ols-figure-caption p {\n      margin: 0;\n      color: #5f6b85;\n      font-size: clamp(15px, 1.2vw, 17px);\n      line-height: 1.6;\n      font-weight: 300;\n      font-style: italic;\n    }\n\n    .ols-table-wrap {\n      overflow-x: auto;\n      border-radius: 22px;\n      border: 1px solid var(--border);\n      background: #ffffff;\n      margin-top: 18px;\n    }\n\n    .ols-table {\n      width: 100%;\n      border-collapse: collapse;\n      min-width: 680px;\n    }\n\n    .ols-table th {\n      background: var(--navy);\n      color: #ffffff;\n      padding: 16px;\n      text-align: left;\n      font-size: 15px;\n      font-weight: 600;\n    }\n\n    .ols-table td {\n      padding: 16px;\n      border-bottom: 1px solid var(--border);\n      font-size: 15px;\n      line-height: 1.5;\n      color: var(--body-text);\n      vertical-align: top;\n    }\n\n    .ols-table tr:last-child td { border-bottom: none; }\n\n    .ols-step-grid {\n      display: grid;\n      grid-template-columns: repeat(4, minmax(0, 1fr));\n      gap: 16px;\n      margin-top: 22px;\n    }\n\n    .ols-step-item {\n      border: 1px solid var(--border);\n      border-radius: 20px;\n      padding: 18px;\n      background: #ffffff;\n      box-shadow: var(--inner-shadow);\n    }\n\n    .ols-step-item span {\n      display: inline-flex;\n      align-items: center;\n      justify-content: center;\n      width: 34px;\n      height: 34px;\n      border-radius: 50%;\n      background: var(--blue);\n      color: #ffffff;\n      font-weight: 700;\n      margin-bottom: 10px;\n      font-size: 14px;\n    }\n\n    .ols-step-item h3 {\n      margin: 0 0 8px;\n      font-size: 18px;\n      line-height: 1.25;\n      color: var(--navy);\n    }\n\n    .ols-step-item p {\n      margin: 0;\n      font-size: 14px;\n      line-height: 1.55;\n    }\n\n    .ols-callout-row {\n      display: grid;\n      grid-template-columns: repeat(2, minmax(0, 1fr));\n      gap: 18px;\n      margin-top: 22px;\n    }\n\n    .ols-callout {\n      border-radius: 22px;\n      padding: 20px;\n      border: 1px solid var(--border);\n      background: linear-gradient(135deg, #ffffff, #f8fbff);\n    }\n\n    .ols-callout.warning {\n      background: linear-gradient(135deg, #ffffff, #fff7ef);\n      border-color: rgba(249, 115, 22, 0.20);\n    }\n\n    .ols-callout h3 {\n      margin: 0 0 8px;\n      font-size: 21px;\n      color: var(--navy);\n    }\n\n    .ols-callout p {\n      margin: 0;\n    }\n\n    .ols-related-grid {\n      display: grid;\n      grid-template-columns: repeat(3, minmax(0, 1fr));\n      gap: 16px;\n      margin-top: 18px;\n    }\n\n    .ols-related-item {\n      border: 1px solid var(--border);\n      border-radius: 18px;\n      padding: 18px;\n      background: #ffffff;\n      color: var(--navy);\n      text-decoration: none;\n      font-weight: 600;\n      line-height: 1.5;\n      transition: transform 0.2s ease, box-shadow 0.2s ease;\n    }\n\n    .ols-related-item:hover {\n      transform: translateY(-2px);\n      box-shadow: 0 10px 22px rgba(28, 36, 75, 0.08);\n    }\n\n    \/* interactive *\/\n    .ols-interactive-shell {\n      margin-top: 24px;\n      border: 1px solid var(--border);\n      border-radius: 26px;\n      background: linear-gradient(135deg, #ffffff, #f8fbff);\n      box-shadow: var(--inner-shadow);\n      overflow: hidden;\n    }\n\n    .ols-interactive-header {\n      padding: 22px 24px 16px;\n      border-bottom: 1px solid var(--border);\n    }\n\n    .ols-interactive-header h3 {\n      margin: 0 0 8px;\n      font-size: 25px;\n      color: var(--navy);\n      line-height: 1.2;\n    }\n\n    .ols-interactive-header p {\n      margin: 0;\n      font-size: 15px;\n      line-height: 1.65;\n      color: var(--body-text);\n    }\n\n    .ols-interactive-body {\n      padding: 20px;\n      display: grid;\n      grid-template-columns: minmax(0, 1fr) 270px;\n      grid-template-areas:\n        \"graph status\"\n        \"controls controls\";\n      gap: 16px;\n      align-items: stretch;\n    }\n\n    .ols-curve-box,\n    .ols-control-box,\n    .ols-status-box {\n      background: #ffffff;\n      border: 1px solid var(--border);\n      border-radius: 22px;\n      padding: 16px;\n      box-shadow: var(--inner-shadow);\n      min-width: 0;\n    }\n\n    .ols-curve-box {\n      grid-area: graph;\n    }\n\n    .ols-status-box {\n      grid-area: status;\n    }\n\n    .ols-control-box {\n      grid-area: controls;\n    }\n\n    .ols-control-box h4,\n    .ols-status-box h4 {\n      margin: 0 0 12px;\n      font-size: 18px;\n      line-height: 1.25;\n      color: var(--navy);\n    }\n\n    .ols-chart-wrap {\n      width: 100%;\n      overflow: hidden;\n      border-radius: 16px;\n      background: #ffffff;\n      border: 1px solid rgba(28, 36, 75, 0.10);\n    }\n\n    .ols-chart-wrap svg {\n      width: 100%;\n      height: auto;\n      display: block;\n    }\n\n    .ols-control-grid {\n      display: grid;\n      grid-template-columns: repeat(4, minmax(0, 1fr));\n      gap: 12px;\n      margin-top: 10px;\n    }\n\n    .ols-pulse-btn,\n    .ols-reset-btn {\n      appearance: none;\n      border: none;\n      cursor: pointer;\n      border-radius: 16px;\n      padding: 14px 14px;\n      font-family: Poppins, Arial, sans-serif;\n      font-size: 15px;\n      font-weight: 700;\n      transition: transform 0.2s ease, box-shadow 0.2s ease, background 0.2s ease;\n      touch-action: manipulation;\n      user-select: none;\n    }\n\n    .ols-pulse-btn {\n      background: linear-gradient(135deg, var(--blue), #5b8cff);\n      color: #ffffff;\n      box-shadow: 0 12px 24px rgba(37, 99, 235, 0.20);\n      animation: olsPulseAction 1.8s infinite;\n    }\n\n    .ols-pulse-btn:hover,\n    .ols-pulse-btn:focus {\n      transform: translateY(-2px);\n      animation-play-state: paused;\n    }\n\n    .ols-pulse-btn:active,\n    .ols-pulse-btn.is-pressed {\n      transform: translateY(1px) scale(0.99);\n      animation-play-state: paused;\n    }\n\n    .ols-reset-btn {\n      background: #ffffff;\n      color: var(--navy);\n      border: 1px solid var(--border);\n      box-shadow: 0 10px 20px rgba(28, 36, 75, 0.08);\n    }\n\n    .ols-reset-btn:hover {\n      transform: translateY(-2px);\n    }\n\n    @keyframes olsPulseAction {\n      0% {\n        transform: scale(1);\n        box-shadow: 0 12px 24px rgba(37, 99, 235, 0.18), 0 0 0 0 rgba(37, 99, 235, 0.18);\n      }\n      50% {\n        transform: scale(1.03);\n        box-shadow: 0 14px 28px rgba(37, 99, 235, 0.22), 0 0 0 12px rgba(37, 99, 235, 0.00);\n      }\n      100% {\n        transform: scale(1);\n        box-shadow: 0 12px 24px rgba(37, 99, 235, 0.18), 0 0 0 0 rgba(37, 99, 235, 0.00);\n      }\n    }\n\n    .ols-stats {\n      display: grid;\n      gap: 12px;\n    }\n\n    .ols-stat {\n      border-radius: 16px;\n      padding: 14px 16px;\n      background: #f8fbff;\n      border: 1px solid rgba(28, 36, 75, 0.08);\n    }\n\n    .ols-stat strong {\n      display: block;\n      color: var(--navy);\n      font-size: 13px;\n      margin-bottom: 5px;\n      text-transform: uppercase;\n      letter-spacing: 0.04em;\n    }\n\n    .ols-stat span {\n      display: block;\n      color: var(--body-text);\n      font-size: 17px;\n      font-weight: 600;\n    }\n\n    .ols-flask-card {\n      margin-top: 16px;\n      border-radius: 18px;\n      padding: 16px;\n      background: linear-gradient(135deg, #ffffff, #f8fbff);\n      border: 1px solid var(--border);\n    }\n\n    .ols-flask-visual {\n      position: relative;\n      width: 120px;\n      height: 132px;\n      margin: 0 auto 12px;\n    }\n\n    .ols-flask-outline {\n      position: absolute;\n      left: 50%;\n      transform: translateX(-50%);\n      width: 92px;\n      height: 118px;\n      border: 4px solid #9ca3af;\n      border-top-width: 6px;\n      border-radius: 14px 14px 25px 25px \/ 16px 16px 30px 30px;\n      background: rgba(255,255,255,0.75);\n      overflow: hidden;\n    }\n\n    .ols-flask-neck {\n      position: absolute;\n      top: 0;\n      left: 50%;\n      transform: translateX(-50%);\n      width: 28px;\n      height: 28px;\n      background: #ffffff;\n      border-left: 4px solid #9ca3af;\n      border-right: 4px solid #9ca3af;\n      border-top: 6px solid #9ca3af;\n      border-radius: 9px 9px 0 0;\n      z-index: 2;\n    }\n\n    .ols-flask-liquid {\n      position: absolute;\n      left: 50%;\n      bottom: 14px;\n      transform: translateX(-50%);\n      width: 72px;\n      height: 30px;\n      border-radius: 0 0 20px 20px;\n      background: #ffffff;\n      opacity: 0.92;\n      transition: background 0.2s ease, height 0.2s ease;\n    }\n\n    .ols-flask-caption {\n      text-align: center;\n      font-size: 14px;\n      line-height: 1.55;\n      color: var(--body-text);\n      margin: 0;\n    }\n\n    .ols-endpoint-note {\n      margin-top: 12px;\n      padding: 12px 14px;\n      border-radius: 16px;\n      background: #fff7ef;\n      border: 1px solid rgba(249, 115, 22, 0.16);\n      font-size: 14px;\n      line-height: 1.6;\n      color: var(--body-text);\n    }\n\n\n    .ols-cp3-lightbox {\n      position: fixed;\n      inset: 0;\n      background: rgba(8, 13, 31, 0.88);\n      backdrop-filter: blur(6px);\n      z-index: 999999;\n      display: none;\n      align-items: center;\n      justify-content: center;\n      padding: 24px;\n    }\n\n    .ols-cp3-lightbox.is-open {\n      display: flex;\n    }\n\n    .ols-cp3-lightbox img {\n      max-width: min(96vw, 1500px);\n      max-height: 92vh;\n      width: auto;\n      height: auto;\n      display: block;\n      border-radius: 18px;\n      box-shadow: 0 30px 90px rgba(0, 0, 0, 0.38);\n      background: #ffffff;\n    }\n\n    .ols-cp3-lightbox button {\n      position: absolute;\n      top: 18px;\n      right: 18px;\n      width: 44px;\n      height: 44px;\n      border-radius: 999px;\n      border: 1px solid rgba(255, 255, 255, 0.35);\n      background: #ffffff;\n      color: var(--navy);\n      font-family: Poppins, Arial, sans-serif;\n      font-size: 26px;\n      line-height: 1;\n      cursor: pointer;\n      font-weight: 800;\n      box-shadow: 0 14px 36px rgba(0, 0, 0, 0.24);\n    }\n\n    .ols-cp3-lightbox button:hover {\n      background: var(--soft-blue);\n    }\n\n    .ols-cp3-lightbox p {\n      position: absolute;\n      left: 28px;\n      right: 84px;\n      bottom: 16px;\n      margin: 0;\n      color: #ffffff;\n      font-size: 14px;\n      line-height: 1.4;\n    }\n\n    @media (max-width: 1050px) {\n      .ols-revision-layout {\n        grid-template-columns: 1fr;\n      }\n\n      .ols-sidebar {\n        position: relative;\n        top: auto;\n      }\n\n      .ols-topic-list {\n        grid-template-columns: repeat(2, minmax(0, 1fr));\n      }\n\n      .ols-main { max-width: none; }\n\n      .ols-step-grid,\n      .ols-callout-row,\n      .ols-related-grid {\n        grid-template-columns: repeat(2, minmax(0, 1fr));\n      }\n\n      .ols-interactive-body {\n        grid-template-columns: 1fr;\n        grid-template-areas:\n          \"graph\"\n          \"status\"\n          \"controls\";\n      }\n    }\n\n    @media (max-width: 760px) {\n      .ols-revision-layout {\n        padding: 14px 12px 44px;\n      }\n\n      .ols-title-card,\n      .ols-note-card,\n      .ols-related-card {\n        padding: 24px 18px;\n        border-radius: 22px;\n      }\n\n      .ols-note-title {\n        align-items: flex-start;\n      }\n\n      .ols-figure-card { border-radius: 22px; }\n      .ols-figure-image { min-height: 240px; padding: 14px; border-radius: 22px 22px 0 0; }\n      .ols-figure-caption { padding: 18px; }\n      .ols-cp3-lightbox { padding: 12px; }\n      .ols-cp3-lightbox p { display: none; }\n\n      .ols-topic-list,\n      .ols-step-grid,\n      .ols-callout-row,\n      .ols-related-grid,\n      .ols-control-grid {\n        grid-template-columns: 1fr;\n      }\n\n      .ols-interactive-header,\n      .ols-interactive-body {\n        padding: 18px;\n      }\n\n      .ols-author {\n        align-items: flex-start;\n        padding: 22px 18px;\n        border-radius: 22px;\n      }\n\n      .ols-author-avatar-img {\n        width: 72px;\n        height: 72px;\n      }\n\n      .ols-author-title {\n        font-size: 24px;\n      }\n\n      .ols-author-description {\n        font-size: 15px;\n      }\n    }\n  <\/style>\n\n  <div class=\"ols-revision-layout\">\n    <aside class=\"ols-sidebar\">\r\n  <div class=\"ols-sidebar-header\">\r\n    <h3>Revision Notes<\/h3>\r\n    <p>Edexcel A Level Chemistry<\/p>\r\n  <\/div>\r\n\r\n  <div class=\"ols-topic-group\">\r\n    <h4>Core Practicals<\/h4>\r\n    <ul class=\"ols-topic-list\">\r\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/core-practicals\/cp-1-molar-volume-of-a-gas\/\">CP1: Molar Volume of a Gas<\/a><\/li>\r\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/core-practicals\/cp-2-prepare-a-standard-solution\/\">CP2: Prepare a Standard Solution<\/a><\/li>\r\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/core-practicals\/cp-3-concentration-of-hcl-by-titration\/\">CP3: Concentration of HCl by Titration<\/a><\/li>\r\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/core-practicals\/cp-4-hydrolysis-of-halogenoalkanes\/\">CP4: Hydrolysis of Halogenoalkanes<\/a><\/li>\r\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/core-practicals\/cp-5-oxidation-of-ethanol\/\">CP5: Oxidation of Ethanol<\/a><\/li>\r\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/core-practicals\/cp-6-chlorination-of-2-methylpropan-2-ol\/\">CP6: Chlorination of 2-methylpropan-2-ol<\/a><\/li>\r\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/core-practicals\/cp-7-analysis-of-inorganic-and-organic-unknowns\/\">CP7: Analysis of Inorganic and Organic Unknowns<\/a><\/li>\r\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/core-practicals\/cp-8-enthalpy-change-via-hess-law\/\">CP8: Enthalpy Change via Hess\u2019s Law<\/a><\/li>\r\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/core-practicals\/cp-9-electrochemical-cells\/\">CP9: Electrochemical Cells<\/a><\/li>\r\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/core-practicals\/cp-10-titration-of-edta\/\">CP10: Titration of EDTA<\/a><\/li>\r\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/core-practicals\/cp-11-rates-of-reaction-clock\/\">CP11: Rates of Reaction (Clock)<\/a><\/li>\r\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/core-practicals\/cp-12-continuous-monitoring-rates\/\">CP12: Continuous Monitoring Rates<\/a><\/li>\r\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/core-practicals\/cp-13-preparation-of-aspirin\/\">CP13: Preparation of Aspirin<\/a><\/li>\r\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/core-practicals\/cp-14-thin-layer-chromatography\/\">CP14: Thin Layer Chromatography<\/a><\/li>\r\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/core-practicals\/cp-15-preparing-organic-compound\/\">CP15: Preparing Organic Compound<\/a><\/li>\r\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/core-practicals\/cp-16-testing-organic-unknowns\/\">CP16: Testing Organic Unknowns<\/a><\/li>\r\n    <\/ul>\r\n  <\/div>\r\n\r\n  <div class=\"ols-topic-group\">\r\n    <h4>Useful Links<\/h4>\r\n    <ul class=\"ols-topic-list\">\r\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/\">Edexcel A Level Chemistry<\/a><\/li>\r\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/core-practicals\/\">Core Practicals<\/a><\/li>\r\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-5-formulae-equations-and-amounts-of-substance\/\">Formulae, Equations and Amounts of Substance<\/a><\/li>\r\n    <\/ul>\r\n  <\/div>\r\n<\/aside>\r\n\r\n<script>\r\n(function () {\r\n  var sidebar = document.querySelector('.ols-sidebar');\r\n  if (!sidebar) return;\r\n\r\n  var currentPath = window.location.pathname.replace(\/\\\/$\/, '');\r\n\r\n  sidebar.querySelectorAll('.ols-topic-list li').forEach(function (li) {\r\n    li.classList.remove('active');\r\n\r\n    var link = li.querySelector('a');\r\n    if (!link) return;\r\n\r\n    var linkPath = new URL(link.href).pathname.replace(\/\\\/$\/, '');\r\n\r\n    if (linkPath === currentPath) {\r\n      li.classList.add('active');\r\n    }\r\n  });\r\n})();\r\n<\/script>\n\n\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\/edexcel\/\">Edexcel<\/a> \/\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/core-practicals\/\">Core Practicals<\/a> \/\n        <span>CP3: Concentration of HCl by Titration<\/span>\n      <\/nav>\n\n      <header class=\"ols-title-card\">\n        <h1>CP3: Finding the Concentration of Hydrochloric Acid<\/h1>\n        <p class=\"ols-page-intro\">A guided walkthrough of Core Practical 3 for Edexcel A Level Chemistry. This page takes you through the dilution step, the titration method, the end point, concordant titres, and the full concentration calculation using sample data.<\/p>\n\n        <div class=\"ols-badges\">\n          <div class=\"ols-badge\">Exam board: Edexcel<\/div>\n          <div class=\"ols-badge\">Paper 3: General and Practical Principles in Chemistry<\/div>\n        <\/div>\n\n        <div class=\"ols-author\">\n          <img decoding=\"async\" class=\"ols-author-avatar-img\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/05\/Author-Profile.jpeg\" alt=\"Dr. Mohammed Al-Fatah\">\n\n          <div class=\"ols-author-content\">\n            <h2 class=\"ols-author-title\">Written by: Dr. Mohammed Al-Fatah<\/h2>\n            <p class=\"ols-author-description\">Chemistry specialist revision notes for A Level Chemistry.<\/p>\n\n            <a class=\"ols-linkedin-pill\" href=\"https:\/\/www.linkedin.com\/in\/doctormohammedfatah\/\" target=\"_blank\" rel=\"noopener noreferrer\">\n              <svg class=\"ols-linkedin-icon\" viewBox=\"0 0 24 24\" fill=\"currentColor\" aria-hidden=\"true\">\n                <path d=\"M4.98 3.5C4.98 4.88 3.86 6 2.48 6S0 4.88 0 3.5 1.12 1 2.48 1s2.5 1.12 2.5 2.5zM.5 8h4V24h-4V8zm7 0h3.8v2.2h.1c.5-.9 1.8-2.2 3.9-2.2 4.2 0 5 2.8 5 6.4V24h-4v-7.6c0-1.8 0-4.2-2.6-4.2s-3 2-3 4v7.8h-4V8z\"><\/path>\n              <\/svg>\n              View LinkedIn Profile\n            <\/a>\n          <\/div>\n        <\/div>\n      <\/header>\n\n      <article class=\"ols-note-card soft\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">1<\/div>\n          <h2>What This Practical Measures<\/h2>\n        <\/div>\n\n        <p>In this practical, you are finding the <strong>concentration of an original hydrochloric acid solution<\/strong>. You do this by first diluting an accurately measured sample of hydrochloric acid, then titrating aliquots of the diluted acid against a <strong>previously standardised sodium hydroxide solution<\/strong>.<\/p>\n\n        <p>The chemical reaction is:<\/p>\n\n        <div class=\"ols-formula-box\">\n          <p><strong>HCl + NaOH \u2192 NaCl + H<sub>2<\/sub>O<\/strong><\/p>\n          <p>This is a <strong>1:1 reaction<\/strong>, so the moles of sodium hydroxide in the titre equal the moles of hydrochloric acid in the aliquot at the end point.<\/p>\n        <\/div>\n\n        <div class=\"ols-step-grid\">\n          <div class=\"ols-step-item\">\n            <span>1<\/span>\n            <h3>Measure<\/h3>\n            <p>Use a pipette to transfer <strong>25.0 cm<sup>3<\/sup><\/strong> of hydrochloric acid accurately.<\/p>\n          <\/div>\n          <div class=\"ols-step-item\">\n            <span>2<\/span>\n            <h3>Dilute<\/h3>\n            <p>Make it up to <strong>250 cm<sup>3<\/sup><\/strong> in a volumetric flask with distilled water.<\/p>\n          <\/div>\n          <div class=\"ols-step-item\">\n            <span>3<\/span>\n            <h3>Titrate<\/h3>\n            <p>Titrate <strong>25.0 cm<sup>3<\/sup><\/strong> aliquots of the diluted acid with standardised NaOH.<\/p>\n          <\/div>\n          <div class=\"ols-step-item\">\n            <span>4<\/span>\n            <h3>Calculate<\/h3>\n            <p>Use the mean titre to calculate the concentration of the <strong>original<\/strong> acid.<\/p>\n          <\/div>\n        <\/div>\n\n        <div class=\"ols-key-box\">\n          <p><strong>Key idea:<\/strong> this practical is really about linking accurate measurements to stoichiometry. If your technique is sound, the calculation becomes straightforward.<\/p>\n        <\/div>\n      <\/article>\n\n      <article class=\"ols-note-card\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">2<\/div>\n          <h2>Apparatus and Safety<\/h2>\n        <\/div>\n\n        <p>You need a burette, clamp and stand, conical flask, 25 cm<sup>3<\/sup> volumetric pipette and safety filler, 250 cm<sup>3<\/sup> volumetric flask, beakers, sodium hydroxide solution, hydrochloric acid solution, phenolphthalein, and distilled water.<\/p>\n\n        <p>Safety matters because both the acid and the alkali can irritate skin and eyes. Sodium hydroxide is especially hazardous to the eyes, so eye protection is essential. You must also use a <strong>pipette filler<\/strong> rather than mouth pipetting.<\/p>\n\n        <div class=\"ols-callout-row\">\n          <div class=\"ols-callout\">\n            <h3>Essential safety<\/h3>\n            <p>Wear goggles, avoid skin contact with the acid, alkali and indicator, and take care when clamping and filling the burette so it does not crack or topple over.<\/p>\n          <\/div>\n          <div class=\"ols-callout warning\">\n            <h3>Technique reminder<\/h3>\n            <p>Record burette readings to the nearest <strong>0.05 cm<sup>3<\/sup><\/strong>. Do not include the rough titre when calculating the mean.<\/p>\n          <\/div>\n        <\/div>\n      <\/article>\n\n      <article class=\"ols-note-card\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">3<\/div>\n          <h2>Step 1: Dilute the Hydrochloric Acid Accurately<\/h2>\n        <\/div>\n\n        <p>Wash out the 250 cm<sup>3<\/sup> volumetric flask with distilled water. Then use a volumetric pipette to transfer <strong>25.0 cm<sup>3<\/sup><\/strong> of the original hydrochloric acid into the flask. Add distilled water until the bottom of the meniscus sits exactly on the mark.<\/p>\n\n        <p>This dilution stage matters because the full 250 cm<sup>3<\/sup> flask now contains all the moles that were originally present in the 25.0 cm<sup>3<\/sup> sample. Later, you will titrate just a <strong>25.0 cm<sup>3<\/sup> aliquot<\/strong> of this diluted solution, so you must scale back up in the final calculation.<\/p>\n\n        <div class=\"ols-key-box\">\n          <p><strong>Remember:<\/strong> do not force out the final drop from the volumetric pipette. The pipette is calibrated so that a small amount remains inside after delivery.<\/p>\n        <\/div>\n\n        <div class=\"ols-figure-card\">\n          <div class=\"ols-figure-image\">\n            <img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/06\/How-to-use-a-volumetric-pipette.webp\" alt=\"How to use a volumetric pipette, including rinsing, using a pipette filler, reading the meniscus, and not forcing out the final drop.\">\n          <\/div>\n          <div class=\"ols-figure-caption\">\n            <h3>Using the volumetric pipette<\/h3>\n            <p>Rinse the pipette with the solution it will contain, set the meniscus at the calibration line, deliver 25.0 cm<sup>3<\/sup>, and do not blow out the final drop.<\/p>\n          <\/div>\n        <\/div>\n      <\/article>\n\n      <article class=\"ols-note-card\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">4<\/div>\n          <h2>Step 2: Set Up and Run the Titration<\/h2>\n        <\/div>\n\n        <p>Prepare the titration apparatus carefully. The <strong>burette should contain the standardised sodium hydroxide solution<\/strong>, and the conical flask should contain <strong>25.0 cm<sup>3<\/sup> of the diluted hydrochloric acid<\/strong>.<\/p>\n\n        <p>Rinse the burette with the sodium hydroxide solution before filling it. Make sure the jet tip is completely filled and contains <strong>no air bubbles<\/strong>. Then pipette a 25.0 cm<sup>3<\/sup> aliquot of the diluted acid into the conical flask and add a few drops of phenolphthalein indicator.<\/p>\n\n        <p>During the titration, swirl the flask continuously. As you approach the end point, add the sodium hydroxide <strong>dropwise<\/strong>.<\/p>\n\n        <div class=\"ols-key-box\">\n          <p><strong>Exam focus:<\/strong> always explain that air in the burette jet makes the delivered volume seem larger than the true reacting volume, giving a titre that is too large.<\/p>\n        <\/div>\n\n        <div class=\"ols-figure-card\">\n          <div class=\"ols-figure-image\">\n            <img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/06\/how-to-use-a-burette-correctly.webp\" alt=\"How to use a burette correctly, including rinsing, removing air bubbles, and reading the bottom of the meniscus.\">\n          <\/div>\n          <div class=\"ols-figure-caption\">\n            <h3>Using the burette correctly<\/h3>\n            <p>Rinse with solution, remove bubbles from the jet, read the bottom of the meniscus at eye level, and record readings to the nearest 0.05 cm<sup>3<\/sup>.<\/p>\n          <\/div>\n        <\/div>\n      <\/article>\n\n      <article class=\"ols-note-card purple\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">5<\/div>\n          <h2>Step 3: Spot the End Point with Phenolphthalein<\/h2>\n        <\/div>\n\n        <p>Phenolphthalein is the correct indicator here. The diluted hydrochloric acid in the conical flask starts acidic, so the indicator is <strong>colourless<\/strong>. As sodium hydroxide is added, the pH rises.<\/p>\n\n        <p>The end point is reached when the solution becomes <strong>pale pink<\/strong> and the colour persists for about <strong>5 seconds<\/strong>. If the pink disappears quickly while swirling, you have not quite reached the end point yet.<\/p>\n\n        <div class=\"ols-callout-row\">\n          <div class=\"ols-callout\">\n            <h3>Before the end point<\/h3>\n            <p>The flask remains colourless. Any pink flashes disappear on swirling.<\/p>\n          <\/div>\n          <div class=\"ols-callout warning\">\n            <h3>At the end point<\/h3>\n            <p>The solution becomes a very faint pink. If the pink is strong, you have probably overshot the end point.<\/p>\n          <\/div>\n        <\/div>\n\n        <div class=\"ols-key-box\">\n          <p><strong>Technique tip:<\/strong> place the conical flask on a white tile or white paper so the faint pink colour change is easier to see.<\/p>\n        <\/div>\n\n        <div class=\"ols-figure-card\">\n          <div class=\"ols-figure-image\">\n            <img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/06\/Using-indicators-in-titrations.webp\" alt=\"Using indicators in titrations, including phenolphthalein and methyl orange colour changes.\">\n          <\/div>\n          <div class=\"ols-figure-caption\">\n            <h3>Phenolphthalein in this practical<\/h3>\n            <p>Phenolphthalein is pink in alkali and colourless in acid. In this titration, the correct end point is the first faint pink that remains for a few seconds.<\/p>\n          <\/div>\n        <\/div>\n      <\/article>\n\n      <article class=\"ols-note-card\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">6<\/div>\n          <h2>Step 4: Record Titres and Choose Concordant Results<\/h2>\n        <\/div>\n\n        <p>You should carry out one rough titration first, then repeat the titration until you obtain at least <strong>two concordant titres<\/strong>. Concordant titres are usually within <strong>0.10 cm<sup>3<\/sup><\/strong> of each other.<\/p>\n\n        <p>Use the sample data below. Trial 1 and Trial 3 are a good concordant pair because 30.10 cm<sup>3<\/sup> and 30.05 cm<sup>3<\/sup> differ by only 0.05 cm<sup>3<\/sup>.<\/p>\n\n        <div class=\"ols-table-wrap\">\n          <table class=\"ols-table\">\n            <thead>\n              <tr>\n                <th>Trial<\/th>\n                <th>Final burette reading \/ cm<sup>3<\/sup><\/th>\n                <th>Initial burette reading \/ cm<sup>3<\/sup><\/th>\n                <th>Titre \/ cm<sup>3<\/sup><\/th>\n              <\/tr>\n            <\/thead>\n            <tbody>\n              <tr>\n                <td>Trial 1<\/td>\n                <td>30.55<\/td>\n                <td>0.45<\/td>\n                <td>30.10<\/td>\n              <\/tr>\n              <tr>\n                <td>Trial 2<\/td>\n                <td>32.10<\/td>\n                <td>2.15<\/td>\n                <td>29.85<\/td>\n              <\/tr>\n              <tr>\n                <td>Trial 3<\/td>\n                <td>30.65<\/td>\n                <td>0.60<\/td>\n                <td>30.05<\/td>\n              <\/tr>\n              <tr>\n                <td>Trial 4<\/td>\n                <td>33.40<\/td>\n                <td>3.15<\/td>\n                <td>30.25<\/td>\n              <\/tr>\n            <\/tbody>\n          <\/table>\n        <\/div>\n\n        <div class=\"ols-formula-box\">\n          <p><strong>Mean titre<\/strong> = (30.10 + 30.05) \u00f7 2<\/p>\n          <p><strong>Mean titre = 30.08 cm<sup>3<\/sup><\/strong> (to 2 d.p.)<\/p>\n        <\/div>\n\n        <div class=\"ols-key-box\">\n          <p><strong>Important:<\/strong> do not average all the values automatically. Choose only the concordant titres and exclude the rough titration.<\/p>\n        <\/div>\n      <\/article>\n\n      <article class=\"ols-note-card soft\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">7<\/div>\n          <h2>Step 5: Worked Calculation from the Mean Titre<\/h2>\n        <\/div>\n\n        <p>Now use the mean titre to calculate the concentration of the original hydrochloric acid. The sodium hydroxide concentration is <strong>0.0800 mol dm<sup>-3<\/sup><\/strong>, and the mean titre is <strong>30.08 cm<sup>3<\/sup><\/strong>.<\/p>\n\n        <div class=\"ols-formula-box\">\n          <p><strong>1. Convert volume to dm<sup>3<\/sup><\/strong><\/p>\n          <p>30.08 cm<sup>3<\/sup> = 0.03008 dm<sup>3<\/sup><\/p>\n        <\/div>\n\n        <div class=\"ols-formula-box\">\n          <p><strong>2. Calculate moles of NaOH in the mean titre<\/strong><\/p>\n          <p>n = c \u00d7 V = 0.0800 \u00d7 0.03008 = 0.0024064 mol<\/p>\n        <\/div>\n\n        <div class=\"ols-formula-box\">\n          <p><strong>3. Use the 1:1 equation<\/strong><\/p>\n          <p>Moles of HCl in the 25.0 cm<sup>3<\/sup> aliquot of diluted acid = 0.0024064 mol<\/p>\n        <\/div>\n\n        <div class=\"ols-formula-box\">\n          <p><strong>4. Scale up from the 25.0 cm<sup>3<\/sup> aliquot to the full 250 cm<sup>3<\/sup> volumetric flask<\/strong><\/p>\n          <p>moles in full 250 cm<sup>3<\/sup> = 0.0024064 \u00d7 (250 \u00f7 25.0)<\/p>\n          <p>= 0.024064 mol<\/p>\n        <\/div>\n\n        <div class=\"ols-formula-box\">\n          <p><strong>5. Calculate the concentration of the original hydrochloric acid<\/strong><\/p>\n          <p>The original 25.0 cm<sup>3<\/sup> sample contained 0.024064 mol.<\/p>\n          <p>c = n \u00f7 V = 0.024064 \u00f7 0.0250 = <strong>0.963 mol dm<sup>-3<\/sup><\/strong><\/p>\n        <\/div>\n\n        <div class=\"ols-callout-row\">\n          <div class=\"ols-callout\">\n            <h3>General scaling rule<\/h3>\n            <p>number of moles in full volume = (full volume \u00d7 number of moles in aliquot) \u00f7 aliquot volume<\/p>\n          <\/div>\n          <div class=\"ols-callout warning\">\n            <h3>Common slip<\/h3>\n            <p>Students often forget the <strong>dilution factor of 10<\/strong> when going from the 25.0 cm<sup>3<\/sup> aliquot to the full 250 cm<sup>3<\/sup> flask.<\/p>\n          <\/div>\n        <\/div>\n      <\/article>\n\n      <article class=\"ols-note-card purple\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">8<\/div>\n          <h2>Evaluation, Uncertainty and Common Errors<\/h2>\n        <\/div>\n\n        <p>A single burette reading has an uncertainty of about <strong>\u00b10.05 cm<sup>3<\/sup><\/strong>. Because a titre uses two readings, the uncertainty in the titre is about <strong>\u00b10.10 cm<sup>3<\/sup><\/strong>.<\/p>\n\n        <div class=\"ols-formula-box\">\n          <p><strong>Percentage burette uncertainty<\/strong><\/p>\n          <p>% uncertainty = (0.10 \u00f7 mean titre) \u00d7 100<\/p>\n          <p>For a mean titre of 30.08 cm<sup>3<\/sup>:<\/p>\n          <p>% uncertainty = (0.10 \u00f7 30.08) \u00d7 100 = <strong>0.33%<\/strong><\/p>\n        <\/div>\n\n        <p>Larger titres reduce percentage uncertainty, which is why a titre around 25 cm<sup>3<\/sup> or more is generally better than a much smaller one.<\/p>\n\n        <ul>\n          <li>Rinse the <strong>burette<\/strong> with the sodium hydroxide solution, not water.<\/li>\n          <li>Rinse the <strong>conical flask<\/strong> only with distilled water between titrations.<\/li>\n          <li>Read the <strong>bottom of the meniscus<\/strong> at eye level.<\/li>\n          <li>Near the end point, add the alkali <strong>dropwise<\/strong>.<\/li>\n          <li>If the flask turns deep pink, you have <strong>overshot<\/strong> and should repeat.<\/li>\n        <\/ul>\n\n        <div class=\"ols-key-box\">\n          <p><strong>Exam focus:<\/strong> if a pipette is blown out, too much acid is transferred, the diluted solution is more concentrated, the titre becomes smaller, and the calculated acid concentration is too high.<\/p>\n        <\/div>\n      <\/article>\n\n<section class=\"ols-note-card olsCp3AutoBlock\" id=\"olsCp3AutoTitration\">\n  <style>\n    \/* ===== CP3 one-button autoplay titration interactive (scoped) ===== *\/\n    .olsCp3AutoBlock { overflow:visible; 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}\n    .olsCp3AutoBlock .olsCp3Flask {\n      position:relative;\n      width:128px;\n      height:170px;\n      margin:0 auto 14px;\n    }\n    .olsCp3AutoBlock .olsCp3FlaskNeck {\n      position:absolute;\n      top:0;\n      left:50%;\n      transform:translateX(-50%);\n      width:32px;\n      height:32px;\n      background:#ffffff;\n      border-left:5px solid #9ca3af;\n      border-right:5px solid #9ca3af;\n      border-top:5px solid #9ca3af;\n      border-radius:10px 10px 0 0;\n      z-index:2;\n    }\n    .olsCp3AutoBlock .olsCp3FlaskOutline {\n      position:absolute;\n      left:50%;\n      top:24px;\n      transform:translateX(-50%);\n      width:108px;\n      height:136px;\n      border:5px solid #9ca3af;\n      border-top-width:5px;\n      border-radius:18px 18px 30px 30px \/ 20px 20px 38px 38px;\n      background:rgba(255,255,255,.82);\n      overflow:hidden;\n    }\n    .olsCp3AutoBlock .olsCp3Liquid {\n      position:absolute;\n      left:50%;\n      bottom:14px;\n      transform:translateX(-50%);\n      width:84px;\n      height:36px;\n      border-radius:0 0 25px 25px;\n      background:#dbeafe;\n      transition:background .22s ease,height .22s ease;\n    }\n    .olsCp3AutoBlock .olsCp3FlaskPanel p {\n      margin:0;\n      font-size:15px;\n      line-height:1.45;\n      color:#111827;\n      font-weight:500;\n    }\n    @media (max-width:900px) {\n      .olsCp3AutoBlock .olsCp3AutoBody {\n        grid-template-columns:1fr;\n        grid-template-areas:\"graph\" \"live\" \"flask\";\n      }\n      .olsCp3AutoBlock .olsCp3FlaskPanel { min-height:240px; }\n    }\n    @media (max-width:640px) {\n      .olsCp3AutoBlock .olsCp3AutoHeader,\n      .olsCp3AutoBlock .olsCp3AutoBody { padding:18px; }\n      .olsCp3AutoBlock .olsCp3LivePanel { padding:18px; }\n      .olsCp3AutoBlock .olsCp3LiveGrid { grid-template-columns:1fr; }\n      .olsCp3AutoBlock .olsCp3StartBtn { font-size:16px; padding:15px 18px; }\n    }\n  <\/style>\n\n  <div class=\"ols-note-title\">\n    <div class=\"ols-note-icon\">9<\/div>\n    <h2>Interactive End Point and Titration Curve<\/h2>\n  <\/div>\n\n  <p>This simplified model shows a <strong>strong acid and strong alkali titration<\/strong>. Press <strong>Begin titration<\/strong> once and the model will automatically add sodium hydroxide, slow down near the end point, move the marker along the pH curve, and change the conical flask colour.<\/p>\n\n  <div class=\"olsCp3AutoShell\">\n    <div class=\"olsCp3AutoHeader\">\n      <h3>Run the model<\/h3>\n      <button class=\"olsCp3StartBtn\" type=\"button\" id=\"olsCp3BeginTitrationBtn\" onclick=\"return window.olsCp3BeginTitration ? window.olsCp3BeginTitration() : false;\">Begin titration<\/button>\n      <p>The animation deliberately slows near <strong>30.05 cm<sup>3<\/sup><\/strong>, where the end point is reached and sodium hydroxide should be added dropwise.<\/p>\n    <\/div>\n\n    <div class=\"olsCp3AutoBody\">\n      <div class=\"olsCp3GraphPanel\">\n        <div class=\"olsCp3ChartWrap\">\n          <svg id=\"olsCp3AutoSvg\" viewBox=\"0 0 720 390\" preserveAspectRatio=\"xMidYMid meet\" role=\"img\" aria-label=\"Animated titration curve showing sodium hydroxide volume against pH.\">\n            <rect x=\"0\" y=\"0\" width=\"720\" height=\"390\" fill=\"#ffffff\"><\/rect>\n            <text x=\"360\" y=\"28\" text-anchor=\"middle\" font-size=\"20\" font-weight=\"850\" fill=\"#1C244B\">Strong acid and strong alkali titration curve<\/text>\n            <rect x=\"503.2\" y=\"44\" width=\"18\" height=\"286\" fill=\"#fff7ed\" opacity=\"0.95\"><\/rect>\n            <text x=\"512\" y=\"62\" text-anchor=\"middle\" font-size=\"12\" font-weight=\"850\" fill=\"#f97316\">end point<\/text>\n            <g stroke=\"rgba(28,36,75,0.08)\" stroke-width=\"1\">\n              <line x1=\"62\" y1=\"330\" x2=\"660\" y2=\"330\"><\/line>\n              <line x1=\"62\" y1=\"289.1\" x2=\"660\" y2=\"289.1\"><\/line>\n              <line x1=\"62\" y1=\"248.3\" x2=\"660\" y2=\"248.3\"><\/line>\n              <line x1=\"62\" y1=\"207.4\" x2=\"660\" y2=\"207.4\"><\/line>\n              <line x1=\"62\" y1=\"166.6\" x2=\"660\" y2=\"166.6\"><\/line>\n              <line x1=\"62\" 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text-anchor=\"end\">4<\/text>\n              <text x=\"45\" y=\"211.4\" text-anchor=\"end\">6<\/text>\n              <text x=\"45\" y=\"170.6\" text-anchor=\"end\">8<\/text>\n              <text x=\"45\" y=\"129.7\" text-anchor=\"end\">10<\/text>\n              <text x=\"45\" y=\"88.9\" text-anchor=\"end\">12<\/text>\n              <text x=\"45\" y=\"48\" text-anchor=\"end\">14<\/text>\n              <text x=\"62\" y=\"354\" text-anchor=\"middle\">0<\/text>\n              <text x=\"211.5\" y=\"354\" text-anchor=\"middle\">10<\/text>\n              <text x=\"361\" y=\"354\" text-anchor=\"middle\">20<\/text>\n              <text x=\"510.5\" y=\"354\" text-anchor=\"middle\">30<\/text>\n              <text x=\"660\" y=\"354\" text-anchor=\"middle\">40<\/text>\n            <\/g>\n            <text x=\"360\" y=\"380\" text-anchor=\"middle\" font-size=\"14\" font-weight=\"850\" fill=\"#1C244B\">Volume of NaOH added \/ cm\u00b3<\/text>\n            <text x=\"18\" y=\"187\" 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<\/div>\n\n      <div class=\"olsCp3LivePanel\">\n        <h4>Live result<\/h4>\n        <div class=\"olsCp3LiveGrid\">\n          <div class=\"olsCp3Stat\"><strong>NaOH added<\/strong><span id=\"olsCp3AutoVolume\">0.00 cm\u00b3<\/span><\/div>\n          <div class=\"olsCp3Stat\"><strong>Indicator colour<\/strong><span id=\"olsCp3AutoColour\">Colourless<\/span><\/div>\n          <div class=\"olsCp3Stat\"><strong>Estimated pH<\/strong><span id=\"olsCp3AutoPH\">1.02<\/span><\/div>\n          <div class=\"olsCp3Stat olsCp3Guidance\"><strong>Guidance<\/strong><span id=\"olsCp3AutoMessage\">Ready to begin. The solution starts acidic and colourless.<\/span><\/div>\n        <\/div>\n      <\/div>\n\n      <div class=\"olsCp3FlaskPanel\">\n        <div class=\"olsCp3Flask\" aria-hidden=\"true\">\n          <div class=\"olsCp3FlaskNeck\"><\/div>\n          <div class=\"olsCp3FlaskOutline\"><div class=\"olsCp3Liquid\" id=\"olsCp3AutoLiquid\"><\/div><\/div>\n        <\/div>\n        <p id=\"olsCp3AutoFlaskText\">Phenolphthalein is colourless in acid.<\/p>\n      <\/div>\n    <\/div>\n  <\/div>\n\n  <script>\n    (function(){\n      var running = false;\n      var volume = 0;\n      var timer = null;\n      var targetEndpoint = 30.08;\n      var LEFT = 62, TOP = 44, WIDTH = 598, HEIGHT = 286;\n\n      function byId(id){ return document.getElementById(id); }\n      function clamp(n,min,max){ return Math.max(min, Math.min(max, n)); }\n      function xFromVolume(v){ return LEFT + (v \/ 40) * WIDTH; }\n      function pHFromVolume(v){\n        if (v < 28) { return 1.02 + (v \/ 28) * 1.20; }\n        if (v < 29.80) { return 2.22 + (v - 28) * 0.50; }\n        if (v < 30.00) { return 3.12 + (v - 29.80) * 10.0; }\n        if (v < 30.08) { return 5.12 + (v - 30.00) * 45.0; }\n        if (v < 30.20) { return 8.72 + (v - 30.08) * 12.0; }\n        return Math.min(12.0, 10.16 + Math.log(1 + (v - 30.20) * 1.25) * 1.15);\n      }\n      function yFromPH(ph){ return TOP + HEIGHT - (clamp(ph,0,14) \/ 14) * HEIGHT; }\n      function colourState(ph, v){\n        if (v >= 29.98 && v <= 30.12) {\n          return {name:'Faint pink', fill:'#f9c2dc', text:'First faint pink: this is the correct end point.'};\n        }\n        if (v > 30.12 || ph > 10) {\n          return {name:'Deep magenta', fill:'#9d174d', text:'Too much alkali has been added. 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