{"id":10542,"date":"2026-09-26T11:33:45","date_gmt":"2026-09-26T10:33:45","guid":{"rendered":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-2-2-group-2-the-alkaline-earth-metals\/tests-for-ions\/"},"modified":"2026-09-26T12:43:21","modified_gmt":"2026-09-26T11:43:21","slug":"tests-for-ions","status":"publish","type":"page","link":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-2-2-group-2-the-alkaline-earth-metals\/tests-for-ions\/","title":{"rendered":"Tests for Ions"},"content":{"rendered":"\n<section class=\"ols-revision-page ols-nature-of-covalent-bonding-9ch0-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<\/style>\n\n  <aside class=\"ols-sidebar\">\n  <div class=\"ols-sidebar-header\">\n    <h3>Revision Notes<\/h3>\n    <p>A Level Chemistry<\/p>\n  <\/div>\n\n  <div class=\"ols-topic-group\">\n    <h4>3.2.2 Group 2<\/h4>\n\n    <ul class=\"ols-topic-list\">\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-2-2-group-2-the-alkaline-earth-metals\/\">3.2.2 Overview<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-2-2-group-2-the-alkaline-earth-metals\/trends-down-groups-1-and-2\/\">Trends Down Groups 1 and 2<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-2-2-group-2-the-alkaline-earth-metals\/reactions-of-the-group-1-and-2-elements\/\">Reactions of the Group 1 and 2 Elements<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-2-2-group-2-the-alkaline-earth-metals\/oxides-hydroxides-and-carbonates\/\">Oxides, Hydroxides and Carbonates<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-2-2-group-2-the-alkaline-earth-metals\/solubility-trends-and-the-sulfate-test\/\">Solubility Trends and the Sulfate Test<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-2-2-group-2-the-alkaline-earth-metals\/thermal-stability-and-flame-colours\/\">Thermal Stability and Flame Colours<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-2-2-group-2-the-alkaline-earth-metals\/tests-for-ions\/\">Tests for Ions<\/a>\n      <\/li>\n    <\/ul>\n  <\/div>\n\n  <div class=\"ols-topic-group\">\n    <h4>Other Sections<\/h4>\n\n    <ul class=\"ols-topic-list\">\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-1-7-oxidation-reduction-and-redox-equations\/\">3.1.7 Oxidation, Reduction and Redox Equations<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-2-3-group-7-17-the-halogens\/\">3.2.3 Group 7 (17)<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-1-2-amount-of-substance\/\">3.1.2 Amount of Substance<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-2-1-periodicity\/\">3.2.1 Periodicity<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-1-4-energetics\/\">3.1.4 Energetics<\/a>\n      <\/li>\n    <\/ul>\n  <\/div>\n<\/aside>\n\n<script>\r\n(function() {\r\n  function normalisePath(path) {\r\n    return String(path || '')\r\n      .split('?')[0]\r\n      .split('#')[0]\r\n      .replace(\/\\\/+$\/, '')\r\n      .toLowerCase();\r\n  }\r\n\r\n  function highlightActive() {\r\n    var sidebar = document.querySelector('.ols-sidebar');\r\n    if (!sidebar) return false;\r\n\r\n    var currentPath = normalisePath(window.location.pathname);\r\n    var links = sidebar.querySelectorAll('a[href]');\r\n    var matched = null;\r\n    var matchedLength = 0;\r\n\r\n    sidebar.querySelectorAll('.active, .active-main, .parent-active').forEach(function(item) {\r\n      item.classList.remove('active', 'active-main', 'parent-active');\r\n    });\r\n\r\n    sidebar.querySelectorAll('a[data-ols-disabled-parent=\"1\"], 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true;\r\n  }\r\n\r\n  if (!highlightActive()) {\r\n    document.addEventListener('DOMContentLoaded', highlightActive);\r\n  }\r\n})();\r\n<\/script>\n\n  <main class=\"ols-main\">\n      <nav class=\"ols-breadcrumbs\" aria-label=\"Breadcrumb\">\n<a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/\">Revision Notes<\/a> \/\n<a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/\">A Level Chemistry<\/a> \/\n<a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/\">AQA<\/a> \/\n<a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-2-2-group-2-the-alkaline-earth-metals\/\">3.2.2 Group 2<\/a> \/\n<span>Tests for Ions<\/span>\n<\/nav>\n\n      <header class=\"ols-title-card\">\n        <h1>Tests for Ions<\/h1>\n        <p class=\"ols-page-intro\">A concise revision guide to the test-tube tests, with ionic equations, for carbonate and hydrogencarbonate, sulfate, halide and ammonium ions, and how to plan the order of tests on an unknown.<\/p>\n\n        <div class=\"ols-badges\">\n<div class=\"ols-badge\">Paper 1 and 3 AQA<\/div>\n<div class=\"ols-badge\">3.2.2 Group 2, the Alkaline Earth Metals<\/div>\n<div class=\"ols-badge\">7405\/1 and 7405\/3<\/div>\n<\/div>\n\n        <div class=\"ols-author\">\n\n    <img decoding=\"async\"\n      class=\"ols-author-avatar-img\"\n      src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/05\/Author-Profile.jpeg\"\n      alt=\"Dr. Mohammed Al-Fatah\"\n    >\n\n    <div class=\"ols-author-content\">\n\n      <h2 class=\"ols-author-title\">\n        Written by:<br><span>Dr. Mohammed Al-Fatah<\/span>\n      <\/h2>\n\n      <p class=\"ols-author-description\">\n        Chemistry specialist revision notes for A Level Chemistry.\n      <\/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: Tests for Gases<\/h2>\n<p>Three quick questions on the gas tests you will use to confirm the results of these ion tests: carbon dioxide, ammonia and hydrogen.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-content\" data-content-id=\"878\"><\/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>Carbonate and Hydrogencarbonate Ions<\/h2>\n<\/div>\n<p>Add a dilute acid (hydrochloric or nitric acid) to the solid or solution. <strong>Effervescence<\/strong> shows a carbonate or hydrogencarbonate; the gas turns <strong>limewater cloudy<\/strong>, confirming carbon dioxide:<\/p>\n<p>CO\u2083\u00b2\u207b + 2H\u207a \u2192 CO\u2082 + H\u2082O &nbsp;&nbsp; HCO\u2083\u207b + H\u207a \u2192 CO\u2082 + H\u2082O<\/p>\n<p>To tell the two apart, add magnesium sulfate solution to the cold solution: carbonate ions give a white precipitate of magnesium carbonate at once, while hydrogencarbonate ions give a precipitate only on heating, because heating converts them to carbonate: 2HCO\u2083\u207b \u2192 CO\u2083\u00b2\u207b + H\u2082O + CO\u2082.<\/p>\n<div class=\"ols-key-box\">\n<p><strong>Exam focus:<\/strong> The observation is &#8220;fizzing&#8221; and the confirmation is &#8220;limewater turns cloudy&#8221;. Both are needed for full marks.<\/p>\n<\/div>\n<\/article>\n<article class=\"ols-note-card soft\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">2<\/div>\n<h2>Sulfate Ions<\/h2>\n<\/div>\n<p>Acidify with dilute hydrochloric acid, then add barium chloride solution. A <strong>white precipitate<\/strong> of barium sulfate confirms sulfate ions: Ba\u00b2\u207a(aq) + SO\u2084\u00b2\u207b(aq) \u2192 BaSO\u2084(s). The acid removes carbonate ions first, because they would also give a white precipitate. The full reasoning is on the <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-2-2-group-2-the-alkaline-earth-metals\/solubility-trends-and-the-sulfate-test\/\">Solubility Trends and the Sulfate Test<\/a> page.<\/p>\n<div class=\"ols-key-box\">\n<p><strong>Remember:<\/strong> Hydrochloric acid, then barium chloride. Never sulfuric acid.<\/p>\n<\/div>\n<\/article>\n<section class=\"ols-h5p-card ols-h5p-inline\">\n<span class=\"ols-h5p-kicker\">Check your understanding<\/span>\n<h2>Check: Carbonate and Sulfate<\/h2>\n<p>Interpret the observations from acid and barium chloride tests on unknown solids, including a case designed to mislead.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-879\" class=\"h5p-iframe\" data-content-id=\"879\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Redox and Groups Summary: Carbonate and Sulfate\"><\/iframe><\/div><\/div>\n<\/section>\n<article class=\"ols-note-card purple\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">3<\/div>\n<h2>Halide Ions<\/h2>\n<\/div>\n<p>Acidify with dilute <strong>nitric acid<\/strong>, then add silver nitrate solution. The colour of the precipitate identifies the halide: <strong>white<\/strong> for chloride, <strong>cream<\/strong> for bromide, <strong>yellow<\/strong> for iodide. Adding ammonia solution confirms the result: silver chloride dissolves in dilute ammonia, silver bromide only in concentrated ammonia, and silver iodide in neither.<\/p>\n<p>Ag\u207a(aq) + Cl\u207b(aq) \u2192 AgCl(s) &nbsp;&nbsp; Ag\u207a(aq) + Br\u207b(aq) \u2192 AgBr(s) &nbsp;&nbsp; Ag\u207a(aq) + I\u207b(aq) \u2192 AgI(s)<\/p>\n<p>Nitric acid is used rather than hydrochloric acid because hydrochloric acid would add chloride ions and give a white precipitate whatever the sample contained. The acid removes carbonate and hydroxide ions, which also precipitate with silver ions. The chemistry of the halides is developed on the <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-2-3-group-7-17-the-halogens\/halide-ions-reducing-agents-and-tests\/\">Halide Ions: Reducing Agents and Tests<\/a> page.<\/p>\n<div class=\"ols-key-box\">\n<p><strong>Exam wording:<\/strong> Say &#8220;acidified silver nitrate solution&#8221;, name the colour, then the ammonia result: &#8220;white precipitate that dissolves in dilute ammonia, so chloride ions&#8221;.<\/p>\n<\/div>\n<\/article>\n<article class=\"ols-note-card\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">4<\/div>\n<h2>Ammonium Ions<\/h2>\n<\/div>\n<p>Add sodium hydroxide solution and warm gently. Ammonium ions give off <strong>ammonia gas<\/strong>, which turns damp red litmus paper blue and has a sharp smell:<\/p>\n<p>NH\u2084\u207a + OH\u207b \u2192 NH\u2083 + H\u2082O<\/p>\n<p>The litmus must be damp, because ammonia only acts as a base once it has dissolved in the water on the paper, and it must be held just above the mouth of the tube, not dipped into the alkaline solution, which would turn it blue by itself.<\/p>\n<div class=\"ols-key-box\">\n<p><strong>Common mistake:<\/strong> Testing the solution instead of the gas. The colour change must come from the ammonia gas reaching the damp litmus.<\/p>\n<\/div>\n<\/article>\n<article class=\"ols-note-card soft\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">5<\/div>\n<h2>Planning the Order of Tests<\/h2>\n<\/div>\n<p>Some ions interfere with the tests for others, so the order matters. Test for carbonate first, because carbonate gives a white precipitate in both the sulfate and the halide tests. Use the right acid: hydrochloric acid before barium chloride, nitric acid before silver nitrate. Test the gas, not the liquid, when a gas is the evidence. Record every observation, including &#8220;no change&#8221;, because a negative result is part of the identification.<\/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\/redox-groups-tests-for-ions.png\" 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\/redox-groups-tests-for-ions.png\" alt=\"Test-tube tests for carbonate, sulfate, halide and ammonium ions with ionic equations\">\n<\/a>\n<\/div>\n<div class=\"ols-zoom-card-caption\"><p>Each test has three parts to record: the reagent, the observation and the ionic equation for what happened.<\/p><\/div>\n<\/div>\n<p>Metal ions in the same sample can be identified by a flame test (Group 1 and 2 metals) or by adding sodium hydroxide solution and watching for a precipitate, as described on the <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-2-2-group-2-the-alkaline-earth-metals\/thermal-stability-and-flame-colours\/\">Thermal Stability and Flame Colours<\/a> and <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-2-2-group-2-the-alkaline-earth-metals\/solubility-trends-and-the-sulfate-test\/\">Solubility Trends<\/a> pages.<\/p>\n<p>These tests are assessed practically in Required practical 4 (tests for ions).<\/p>\n<div class=\"ols-key-box\">\n<p><strong>Technique point:<\/strong> A test is only valid when the reagent could not have produced the observation on its own. That is why the acid is always named and always added first.<\/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: Identifying an Unknown<\/h2>\n<p>Work through the results of a sequence of tests on an unknown salt and name both ions.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-content\" data-content-id=\"880\"><\/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>Common Exam Points<\/h2>\n<\/div>\n<h3>Describe the test for a halide ion<\/h3><p>Add dilute nitric acid, then silver nitrate solution; a white, cream or yellow precipitate forms for chloride, bromide or iodide; confirm with dilute and concentrated ammonia.<\/p>\n<h3>Explain why nitric acid is used and not hydrochloric acid<\/h3><p>Hydrochloric acid contains chloride ions, which would give a white precipitate with silver ions whatever the sample.<\/p>\n<h3>Write the ionic equation for the ammonium test<\/h3><p>NH\u2084\u207a + OH\u207b \u2192 NH\u2083 + H\u2082O.<\/p>\n<h3>Do not say<\/h3><p>&#8220;Add silver nitrate then hydrochloric acid&#8221;; &#8220;the litmus paper is dipped into the solution&#8221;; &#8220;carbon dioxide turns limewater milky&#8221; without stating the fizzing first.<\/p>\n<\/article>\n<section class=\"ols-faq-card\">\n<h2>FAQs<\/h2>\n<p>Use these quick answers to check the tests for ions.<\/p>\n\n<div class=\"ols-faq-list\">\n<div class=\"ols-faq-item\">\n<h3>Why is nitric acid used in the halide test?<\/h3>\n<p>Hydrochloric acid contains chloride ions, which would give a white precipitate with silver ions. Nitric acid removes carbonate and hydroxide ions without adding a halide.<\/p>\n<\/div>\n\n<div class=\"ols-faq-item\">\n<h3>Why test for carbonate before sulfate?<\/h3>\n<p>Carbonate ions give a white precipitate with barium ions, so they must be removed by acid before barium chloride is added.<\/p>\n<\/div>\n\n<div class=\"ols-faq-item\">\n<h3>How do I test for ammonium ions?<\/h3>\n<p>Add sodium hydroxide solution and warm; ammonia gas is given off and turns damp red litmus paper blue.<\/p>\n<\/div>\n\n<div class=\"ols-faq-item\">\n<h3>How do I tell a carbonate from a hydrogencarbonate?<\/h3>\n<p>Both fizz with acid. Add magnesium sulfate solution: carbonate ions give a precipitate in the cold, hydrogencarbonate ions only on heating.<\/p>\n<\/div>\n\n<div class=\"ols-faq-item\">\n<h3>What confirms a halide after the silver nitrate test?<\/h3>\n<p>Ammonia solution: silver chloride dissolves in dilute ammonia, silver bromide in concentrated ammonia, silver iodide in neither.<\/p>\n<\/div>\n<\/div>\n<\/section>\n<section class=\"ols-related-card\">\n<h2>Related 3.2.2 Group 2 Pages<\/h2>\n<p>Use these pages to connect the ideas across 3.2.2 Group 2 and the rest of the course.<\/p>\n<div class=\"ols-related-grid\">\n<a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-2-2-group-2-the-alkaline-earth-metals\/trends-down-groups-1-and-2\/\">Trends Down Groups 1 and 2<\/a>\n<a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-2-2-group-2-the-alkaline-earth-metals\/reactions-of-the-group-1-and-2-elements\/\">Reactions of the Group 1 and 2 Elements<\/a>\n<a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-2-2-group-2-the-alkaline-earth-metals\/oxides-hydroxides-and-carbonates\/\">Oxides, Hydroxides and Carbonates<\/a>\n<a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-2-2-group-2-the-alkaline-earth-metals\/solubility-trends-and-the-sulfate-test\/\">Solubility Trends and the Sulfate Test<\/a>\n<a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-2-2-group-2-the-alkaline-earth-metals\/thermal-stability-and-flame-colours\/\">Thermal Stability and Flame Colours<\/a>\n<a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-2-2-group-2-the-alkaline-earth-metals\/\">3.2.2 Group 2 Overview<\/a>\n<a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-1-2-amount-of-substance\/concentration-and-titration-calculations\/titration-calculations\/\">Titration Calculations (3.1.2)<\/a>\n<\/div>\n<\/section>\n<section class=\"ols-attribution-card\">\n        <p><strong>Copyright and author footprint:<\/strong> This OLS revision page was written for Online Learning System by <strong>Dr. Mohammed Al-Fatah<\/strong>. It is designed for A Level Chemistry revision and should not be copied or redistributed without permission.<\/p>\n      <\/section>\n\n      <div class=\"ols-image-lightbox\" id=\"olsImageLightboxNatureCovalentBonding9ch0\" aria-hidden=\"true\" role=\"dialog\" aria-modal=\"true\" aria-label=\"Expanded revision image\">\n        <div class=\"ols-image-lightbox-inner\">\n          <button class=\"ols-image-lightbox-close\" type=\"button\" aria-label=\"Close enlarged image\">\u00d7<\/button>\n          <img decoding=\"async\" class=\"ols-image-lightbox-img\" src=\"\" alt=\"\">\n        <\/div>\n      <\/div>\n\n      <script>\n        (function(){\n          var page = document.querySelector(\".ols-nature-of-covalent-bonding-9ch0-page\");\n          if (!page) { return; }\n          var lightbox = page.querySelector(\"#olsImageLightboxNatureCovalentBonding9ch0\");\n          if (!lightbox) { return; }\n          var lightboxImage = lightbox.querySelector(\".ols-image-lightbox-img\");\n    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