Advanced

Tutor model

i62 💰:9.4

i52 💰:7.9

🏆 i67 💰:62.5

i70 💰:125.0

i68 💰:125.0

🏆 i66 💰:75.0

i65 💰:125.0

i63 💰:62.5

i61 💰:75.0

i60 💰:9.4

i60 💰:37.5

i58 💰:62.5

i57 💰:22.5

i57 💰:37.5

i56 💰:45.0

⚡ i55 💰:11.25

i55 💰:37.5

i54 💰:62.5

i52 💰:35.0

i51 💰:37.5

i49 💰:15.0

i49 💰:62.5

i48 💰:11.3

i47 💰:7.5

i44 💰:25.0

i43 💰:37.5

i42 💰:187.5

i40 💰:5.0

i39 💰:100.0

i38 💰:37.5

i37 💰:11.0

i36 💰:187.5

i34 💰:12.5

i33 💰:37.5

i30 💰:1.0

i29 💰:1.5

i28 💰:150.0

i23 💰:20.0

i20 💰:4.0

i18 💰:1.0

i16 💰:25.0

i13 💰:1.5

Keep session private

What would you like to learn?

Override for the tutor's lesson content generation calls. Auto uses the system default (Claude Sonnet 5 for lesson text, Opus 5 for diagrams).

Lesson generation model

System default

i58 💰:18.8

i31 💰:11.0

i25 💰:31.3

Tutoring abilities

Stomach acid contains hydrochloric acid that can dissolve metal, while salad dressing is soaked in ethanoic acid that you eat every day.

Both are acids, so why does one destroy tissue while the other tastes great on lettuce?

An **acid** is any substance that releases hydrogen ions ($\text{H}^+$) when dissolved in water.

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta name="aspect-ratio" content="1:1">
  <style>
    * { box-sizing: border-box; margin: 0; padding: 0; }
    body {
      width: 100%;
      height: 100%;
      font-family: system-ui, -apple-system, sans-serif;
      background: #f8f9fa;
      color: #1e2945;
      padding: 10px;
      display: flex;
      flex-direction: column;
      justify-content: space-between;
      user-select: none;
      -webkit-user-select: none;
    }

    .header-row {
      display: flex;
      justify-content: space-between;
      align-items: center;
      margin-bottom: 8px;
    }

    .legend {
      display: flex;
      gap: 12px;
      font-size: 12px;
      font-weight: 600;
      background: #ffffff;
      padding: 4px 10px;
      border-radius: 20px;
      border: 1px solid #e2e8f0;
    }

    .legend-item {
      display: flex;
      align-items: center;
      gap: 5px;
    }

    .dot {
      width: 10px;
      height: 10px;
      border-radius: 50%;
      display: inline-block;
    }
    .dot-h { background: #ef4444; box-shadow: 0 0 6px rgba(239, 68, 68, 0.6); }
    .dot-cl { background: #3b82f6; }
    .dot-neutral { background: #94a3b8; }
    .dot-ace { background: #10b981; }

    .grid {
      display: grid;
      grid-template-columns: 1fr 1fr;
      gap: 8px;
      flex: 1;
      min-height: 250px;
    }

    .acid-col {
      display: flex;
      flex-direction: column;
      background: #ffffff;
      border-radius: 12px;
      border: 1px solid #e2e8f0;
      padding: 8px;
      position: relative;
    }

    .acid-title {
      font-size: 13px;
      font-weight: 700;
      text-align: center;
      color: #0f172a;
      line-height: 1.2;
    }

    .formula {
      font-size: 11px;
      color: #64748b;
      font-weight: 600;
      text-align: center;
      margin-bottom: 4px;
    }

    .beaker {
      flex: 1;
      background: linear-gradient(180deg, #f0f9ff 0%, #e0f2fe 100%);
      border: 2px solid #93c5fd;
      border-top: none;
      border-radius: 0 0 10px 10px;
      position: relative;
      overflow: hidden;
      margin: 4px 0 6px 0;
      min-height: 160px;
    }

    .water-line {
      position: absolute;
      top: 10px;
      left: 0;
      right: 0;
      height: 2px;
      background: rgba(59, 130, 246, 0.25);
      border-top: 1px dashed rgba(59, 130, 246, 0.4);
    }

    .badge {
      display: inline-block;
      text-align: center;
      font-size: 11px;
      font-weight: 700;
      padding: 4px 8px;
      border-radius: 6px;
      letter-spacing: 0.2px;
    }

    .badge-strong {
      background: #fee2e2;
      color: #b91c1c;
      border: 1px solid #fca5a5;
    }

    .badge-weak {
      background: #f1f5f9;
      color: #475569;
      border: 1px solid #cbd5e1;
    }

    /* Particles */
    .particle {
      position: absolute;
      display: flex;
      align-items: center;
      justify-content: center;
      font-size: 9px;
      font-weight: 800;
      color: #ffffff;
      border-radius: 50%;
      transition: transform 3s cubic-bezier(0.4, 0, 0.2, 1);
    }

    .p-h {
      width: 17px;
      height: 17px;
      background: #ef4444;
      box-shadow: 0 0 8px rgba(239, 68, 68, 0.7);
      z-index: 2;
    }

    .p-cl {
      width: 22px;
      height: 22px;
      background: #3b82f6;
      box-shadow: 0 1px 3px rgba(0, 0, 0, 0.2);
    }

    .p-ace {
      width: 24px;
      height: 24px;
      background: #10b981;
      font-size: 8px;
      box-shadow: 0 1px 3px rgba(0, 0, 0, 0.2);
    }

    /* Intact molecule */
    .molecule-pair {
      position: absolute;
      display: flex;
      align-items: center;
      gap: 1px;
      padding: 2px 4px;
      background: rgba(255, 255, 255, 0.85);
      border: 1.5px solid #94a3b8;
      border-radius: 12px;
      box-shadow: 0 1px 3px rgba(0, 0, 0, 0.08);
      font-size: 8.5px;
      font-weight: 700;
      color: #334155;
      transition: transform 3s cubic-bezier(0.4, 0, 0.2, 1);
    }

    .ctrl-bar {
      margin-top: 6px;
      display: flex;
      justify-content: center;
      gap: 8px;
    }

    .btn {
      background: #ffffff;
      border: 1px solid #cbd5e1;
      padding: 5px 14px;
      font-size: 12px;
      font-weight: 600;
      color: #334155;
      border-radius: 6px;
      cursor: pointer;
    }
    .btn:active {
      background: #f1f5f9;
    }
  </style>
</head>
<body>

  <div class="header-row">
    <div class="legend">
      <div class="legend-item"><span class="dot dot-h"></span> H⁺</div>
      <div class="legend-item"><span class="dot dot-cl"></span> Cl⁻</div>
      <div class="legend-item"><span class="dot dot-neutral"></span> Intact</div>
    </div>
  </div>

  <div class="grid">
    
    <div class="acid-col">
      <div class="acid-title">Hydrochloric Acid</div>
      <div class="formula">HCl (Strong)</div>
      
      <div class="beaker" id="beakerHcl">
        <div class="water-line"></div>
        
      </div>
      
      <div class="badge badge-strong">100% separated</div>
    </div>

    
    <div class="acid-col">
      <div class="acid-title">Ethanoic Acid</div>
      <div class="formula">CH₃COOH (Weak)</div>
      
      <div class="beaker" id="beakerEth">
        <div class="water-line"></div>
        
      </div>
      
      <div class="badge badge-weak">Mostly intact</div>
    </div>
  </div>

  <div class="ctrl-bar">
    <button class="btn" id="mixBtn">Stir Solution</button>
  </div>

  <script>
    const hclContainer = document.getElementById('beakerHcl');
    const ethContainer = document.getElementById('beakerEth');

    // 6 dissociated pairs for HCl
    const hclIons = [
      { type: 'h', label: 'H⁺', x: 20, y: 30 },
      { type: 'cl', label: 'Cl⁻', x: 65, y: 25 },
      { type: 'h', label: 'H⁺', x: 75, y: 55 },
      { type: 'cl', label: 'Cl⁻', x: 25, y: 60 },
      { type: 'h', label: 'H⁺', x: 15, y: 80 },
      { type: 'cl', label: 'Cl⁻', x: 55, y: 78 },
      { type: 'h', label: 'H⁺', x: 45, y: 40 },
      { type: 'cl', label: 'Cl⁻', x: 80, y: 75 },
      { type: 'h', label: 'H⁺', x: 40, y: 70 },
      { type: 'cl', label: 'Cl⁻', x: 15, y: 45 },
      { type: 'h', label: 'H⁺', x: 60, y: 45 },
      { type: 'cl', label: 'Cl⁻', x: 45, y: 15 }
    ];

    // Ethanoic acid: 1 H+, 1 CH3COO-, 5 intact CH3COOH
    const ethParticles = [
      { kind: 'ion', type: 'h', label: 'H⁺', x: 68, y: 32 },
      { kind: 'ion', type: 'ace', label: 'Ac⁻', x: 22, y: 28 },
      { kind: 'pair', label: 'CH₃COOH', x: 15, y: 55 },
      { kind: 'pair', label: 'CH₃COOH', x: 52, y: 52 },
      { kind: 'pair', label: 'CH₃COOH', x: 25, y: 78 },
      { kind: 'pair', label: 'CH₃COOH', x: 65, y: 76 },
      { kind: 'pair', label: 'CH₃COOH', x: 42, y: 20 }
    ];

    const hclEls = [];
    const ethEls = [];

    // Spawn HCl elements
    hclIons.forEach(item => {
      const el = document.createElement('div');
      el.className = `particle p-${item.type}`;
      el.textContent = item.label;
      el.style.left = item.x + '%';
      el.style.top = item.y + '%';
      hclContainer.appendChild(el);
      hclEls.push({ el, origX: item.x, origY: item.y });
    });

    // Spawn Ethanoic acid elements
    ethParticles.forEach(item => {
      const el = document.createElement('div');
      if (item.kind === 'ion') {
        el.className = `particle p-${item.type}`;
        el.textContent = item.label;
      } else {
        el.className = 'molecule-pair';
        el.textContent = item.label;
      }
      el.style.left = item.x + '%';
      el.style.top = item.y + '%';
      ethContainer.appendChild(el);
      ethEls.push({ el, origX: item.x, origY: item.y });
    });

    // Calm floating animation
    let tick = 0;
    function floatParticles() {
      tick++;
      hclEls.forEach((p, idx) => {
        const dx = Math.sin(tick * 0.03 + idx) * 6;
        const dy = Math.cos(tick * 0.03 + idx * 1.5) * 5;
        p.el.style.transform = `translate(${dx}px, ${dy}px)`;
      });

      ethEls.forEach((p, idx) => {
        const dx = Math.cos(tick * 0.025 + idx * 1.2) * 5;
        const dy = Math.sin(tick * 0.025 + idx) * 4;
        p.el.style.transform = `translate(${dx}px, ${dy}px)`;
      });
    }

    setInterval(floatParticles, 100);

    // Interactive stir
    document.getElementById('mixBtn').addEventListener('click', () => {
      tick += 15;
      floatParticles();
    });
  </script>
</body>
</html>

What causes this drastic difference in how many hydrogen ions actually get released into solution?

In 1884, Swedish chemist Svante Arrhenius discovered that certain molecules split entirely into free ions when mixed with water to conduct electricity.

A **strong acid** is an acid that is **completely ionized** in aqueous solution, meaning every single acid molecule splits apart into ions.

For example, when hydrochloric acid ($\text{HCl}$) dissolves in water, $100\%$ of the molecules separate into hydrogen ions ($\text{H}^+$) and chloride ions ($\text{Cl}^-$):

$$\text{HCl}_{\text{(aq)}} \rightarrow \text{H}^+_{\text{(aq)}} + \text{Cl}^-_{\text{(aq)}}$$

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Strong Acid Ionization</title>
  <style>
    * { box-sizing: border-box; margin: 0; padding: 0; }
    body {
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
      background: #f8fafc;
      color: #0f172a;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: space-between;
      min-height: 100vh;
      padding: 10px 8px;
    }

    .stepper-nav {
      display: flex;
      gap: 6px;
      margin-bottom: 6px;
      flex-wrap: wrap;
      justify-content: center;
    }
    .step-btn {
      background: #ffffff;
      border: 1.5px solid #94a3b8;
      border-radius: 20px;
      padding: 5px 12px;
      font-size: 12px;
      font-weight: 700;
      color: #1e293b;
      cursor: pointer;
      box-shadow: 0 1px 2px rgba(0,0,0,0.05);
      transition: background-color 0.2s ease, border-color 0.2s ease, color 0.2s ease;
    }
    .step-btn.active {
      background: #0284c7;
      border-color: #0284c7;
      color: #ffffff;
      box-shadow: 0 2px 4px rgba(2,132,199,0.3);
    }

    .flow-container {
      width: 100%;
      max-width: 600px;
      display: grid;
      grid-template-columns: 1fr auto 1fr;
      align-items: center;
      gap: 8px;
      position: relative;
    }

    .beaker-card {
      background: #ffffff;
      border: 2px solid #cbd5e1;
      border-radius: 12px;
      padding: 8px 6px;
      display: flex;
      flex-direction: column;
      align-items: center;
      transition: border-color 0.25s ease, box-shadow 0.25s ease, opacity 0.25s ease;
      min-height: 190px;
    }
    .beaker-card.active {
      border-color: #0284c7;
      box-shadow: 0 0 0 3px rgba(2,132,199,0.2);
      opacity: 1 !important;
    }

    .stage-title {
      font-size: 12px;
      font-weight: 800;
      color: #0f172a;
      margin-bottom: 6px;
      text-transform: uppercase;
      letter-spacing: 0.4px;
      text-align: center;
    }

    .beaker {
      width: 100%;
      max-width: 160px;
      height: 140px;
      background: #f0f9ff;
      border: 2.5px solid #64748b;
      border-top: none;
      border-radius: 0 0 14px 14px;
      position: relative;
      overflow: hidden;
    }

    .water-line {
      position: absolute;
      top: 14px;
      left: 0;
      right: 0;
      height: 2px;
      background: rgba(2, 132, 199, 0.35);
      border-bottom: 1px dashed #0284c7;
    }

    .ion-h {
      width: 20px;
      height: 20px;
      background: #dc2626;
      color: #ffffff;
      border-radius: 50%;
      display: flex;
      align-items: center;
      justify-content: center;
      font-size: 10px;
      font-weight: 800;
      box-shadow: 0 1px 2px rgba(220,38,38,0.4);
      z-index: 2;
      flex-shrink: 0;
    }

    .ion-cl {
      width: 24px;
      height: 24px;
      background: #1d4ed8;
      color: #ffffff;
      border-radius: 50%;
      display: flex;
      align-items: center;
      justify-content: center;
      font-size: 10px;
      font-weight: 800;
      box-shadow: 0 1px 2px rgba(29,78,216,0.4);
      z-index: 1;
      flex-shrink: 0;
    }

    .molecule-hcl {
      position: absolute;
      display: flex;
      align-items: center;
      transform: translate(-50%, -50%);
    }
    .molecule-hcl .ion-h {
      margin-right: -6px;
    }

    .free-ion {
      position: absolute;
      transform: translate(-50%, -50%);
    }

    .arrow-card {
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      padding: 4px 2px;
      min-width: 80px;
      transition: opacity 0.25s ease;
    }
    .arrow-symbol {
      font-size: 28px;
      line-height: 1;
      color: #0369a1;
      font-weight: 900;
    }
    .arrow-label {
      font-size: 10.5px;
      font-weight: 800;
      color: #ffffff;
      background: #0284c7;
      border-radius: 6px;
      padding: 3px 6px;
      margin-top: 5px;
      text-align: center;
      white-space: nowrap;
      box-shadow: 0 1px 2px rgba(2,132,199,0.3);
    }
    .arrow-card.active .arrow-label {
      background: #0369a1;
      box-shadow: 0 0 0 2px rgba(3,105,161,0.25);
    }

    .legend {
      display: flex;
      justify-content: center;
      flex-wrap: wrap;
      gap: 14px;
      margin: 6px 0 4px;
      font-size: 12px;
      font-weight: 700;
      color: #1e293b;
    }
    .legend-item {
      display: flex;
      align-items: center;
      gap: 6px;
    }
    .legend-dot {
      width: 12px;
      height: 12px;
      border-radius: 50%;
    }

    .badge-summary {
      background: #0f172a;
      color: #ffffff;
      font-size: 12.5px;
      font-weight: 700;
      text-align: center;
      padding: 8px 12px;
      border-radius: 8px;
      width: 100%;
      max-width: 580px;
      letter-spacing: 0.2px;
      box-shadow: 0 2px 4px rgba(15,23,42,0.15);
    }

    @media (max-width: 440px) {
      .flow-container { gap: 4px; }
      .stage-title { font-size: 10.5px; margin-bottom: 4px; }
      .beaker-card { padding: 6px 3px; min-height: 175px; }
      .beaker { height: 128px; }
      .arrow-card { min-width: 68px; }
      .arrow-symbol { font-size: 22px; }
      .arrow-label { font-size: 9.5px; padding: 2px 4px; }
      .badge-summary { font-size: 11px; padding: 6px 8px; }
      .ion-h { width: 18px; height: 18px; font-size: 9px; }
      .ion-cl { width: 21px; height: 21px; font-size: 9px; }
      .step-btn { padding: 4px 8px; font-size: 11px; }
      .legend { font-size: 11px; gap: 10px; }
    }
  </style>
</head>
<body>

  
  <div class="stepper-nav">
    <button class="step-btn active" onclick="setStep(0)">1: Intact HCl</button>
    <button class="step-btn" onclick="setStep(1)">2: Ionization</button>
    <button class="step-btn" onclick="setStep(2)">3: 100% Free Ions</button>
  </div>

  
  <div class="flow-container">
    
    <div class="beaker-card active" id="card-before">
      <div class="stage-title">5 HCl in Water</div>
      <div class="beaker">
        <div class="water-line"></div>
        
        <div class="molecule-hcl" style="top: 30%; left: 30%;">
          <div class="ion-h">H⁺</div>
          <div class="ion-cl">Cl⁻</div>
        </div>
        <div class="molecule-hcl" style="top: 30%; left: 70%;">
          <div class="ion-h">H⁺</div>
          <div class="ion-cl">Cl⁻</div>
        </div>
        <div class="molecule-hcl" style="top: 54%; left: 50%;">
          <div class="ion-h">H⁺</div>
          <div class="ion-cl">Cl⁻</div>
        </div>
        <div class="molecule-hcl" style="top: 78%; left: 30%;">
          <div class="ion-h">H⁺</div>
          <div class="ion-cl">Cl⁻</div>
        </div>
        <div class="molecule-hcl" style="top: 78%; left: 70%;">
          <div class="ion-h">H⁺</div>
          <div class="ion-cl">Cl⁻</div>
        </div>
      </div>
    </div>

    
    <div class="arrow-card" id="card-arrow">
      <div class="arrow-symbol">➔</div>
      <div class="arrow-label">100% Ionization</div>
    </div>

    
    <div class="beaker-card" id="card-after">
      <div class="stage-title">5 H⁺ &amp; 5 Cl⁻ Free</div>
      <div class="beaker">
        <div class="water-line"></div>
        
        <div class="free-ion ion-h" style="top: 28%; left: 24%;">H⁺</div>
        <div class="free-ion ion-h" style="top: 30%; left: 78%;">H⁺</div>
        <div class="free-ion ion-h" style="top: 52%; left: 50%;">H⁺</div>
        <div class="free-ion ion-h" style="top: 74%; left: 26%;">H⁺</div>
        <div class="free-ion ion-h" style="top: 86%; left: 74%;">H⁺</div>

        
        <div class="free-ion ion-cl" style="top: 26%; left: 52%;">Cl⁻</div>
        <div class="free-ion ion-cl" style="top: 48%; left: 22%;">Cl⁻</div>
        <div class="free-ion ion-cl" style="top: 50%; left: 78%;">Cl⁻</div>
        <div class="free-ion ion-cl" style="top: 72%; left: 68%;">Cl⁻</div>
        <div class="free-ion ion-cl" style="top: 88%; left: 36%;">Cl⁻</div>
      </div>
    </div>
  </div>

  
  <div class="legend">
    <div class="legend-item">
      <div class="legend-dot" style="background:#dc2626;"></div>
      <span>Hydrogen ion (H⁺)</span>
    </div>
    <div class="legend-item">
      <div class="legend-dot" style="background:#1d4ed8;"></div>
      <span>Chloride ion (Cl⁻)</span>
    </div>
  </div>

  
  <div class="badge-summary">
    Strong Acid = No intact acid molecules left in water
  </div>

  <script>
    let currentStep = 0;
    const buttons = document.querySelectorAll('.step-btn');
    const cardBefore = document.getElementById('card-before');
    const cardArrow = document.getElementById('card-arrow');
    const cardAfter = document.getElementById('card-after');

    function updateView() {
      buttons.forEach((btn, idx) => {
        btn.classList.toggle('active', idx === currentStep);
      });

      if (currentStep === 0) {
        cardBefore.classList.add('active');
        cardBefore.style.opacity = '1';
        cardArrow.classList.remove('active');
        cardArrow.style.opacity = '0.55';
        cardAfter.classList.remove('active');
        cardAfter.style.opacity = '0.55';
      } else if (currentStep === 1) {
        cardBefore.classList.remove('active');
        cardBefore.style.opacity = '0.75';
        cardArrow.classList.add('active');
        cardArrow.style.opacity = '1';
        cardAfter.classList.remove('active');
        cardAfter.style.opacity = '0.75';
      } else {
        cardBefore.classList.remove('active');
        cardBefore.style.opacity = '0.55';
        cardArrow.classList.remove('active');
        cardArrow.style.opacity = '0.55';
        cardAfter.classList.add('active');
        cardAfter.style.opacity = '1';
      }
    }

    function setStep(index) {
      currentStep = index;
      updateView();
    }

    // Auto-cycle gently to demonstrate complete reaction sequence
    let cycleTimer = setInterval(() => {
      currentStep = (currentStep + 1) % 3;
      updateView();
    }, 3500);

    // Stop auto-cycling upon user interaction
    buttons.forEach(btn => {
      btn.addEventListener('click', () => {
        clearInterval(cycleTimer);
      });
    });

    updateView();
  </script>
</body>
</html>

Notice the single forward arrow ($\rightarrow$) — the reaction goes to completion and does not reverse.

Common strong acids you must know include hydrochloric acid ($\text{HCl}$), sulfuric acid ($\text{H}_2\text{SO}_4$), and nitric acid ($\text{HNO}_3$).

What happens when an acid refuses to give up all its hydrogen ions?

A **weak acid** is only **partially ionized** in aqueous solution, so only a tiny fraction of its molecules break apart.

In ethanoic acid ($\text{CH}_3\text{COOH}$), roughly $1\%$ of the molecules split into ions, while the remaining $99\%$ stay joined as neutral molecules:

$$\text{CH}_3\text{COOH}_{\text{(aq)}} \rightleftharpoons \text{H}^+_{\text{(aq)}} + \text{CH}_3\text{COO}^-_{\text{(aq)}}$$

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Reversible Equilibrium in Weak Acids</title>
  <style>
    * { 
      box-sizing: border-box; 
      margin: 0; 
      padding: 0; 
    }
    
    body {
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
      color: #0f172a;
      background: transparent;
      padding: 12px 8px;
      display: flex;
      flex-direction: column;
      gap: 14px;
      max-width: 540px;
      margin: 0 auto;
    }

    /* Chemical Formula Styling */
    .chem-formula {
      font-family: "Cambria", "Times New Roman", serif;
      font-weight: 600;
      letter-spacing: 0.3px;
      font-size: 1.12rem;
      white-space: nowrap;
    }
    .chem-formula sub {
      font-size: 0.72em;
      bottom: -0.2em;
      position: relative;
    }
    .chem-formula sup {
      font-size: 0.72em;
      top: -0.35em;
      position: relative;
    }
    .state {
      font-size: 0.8em;
      font-style: italic;
      color: #64748b;
      font-weight: 400;
      margin-left: 1px;
    }

    /* Equation Section */
    .equation-section {
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 8px;
    }

    .eq-display {
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 8px;
      flex-wrap: wrap;
      background: rgba(239, 246, 255, 0.7);
      padding: 10px 14px;
      border-radius: 8px;
      width: 100%;
    }

    .eq-plus {
      color: #64748b;
      font-weight: 600;
      font-size: 1.1rem;
    }

    .eq-symbol-wrap {
      display: inline-flex;
      flex-direction: column;
      align-items: center;
      position: relative;
    }

    .eq-symbol {
      display: inline-flex;
      align-items: center;
      justify-content: center;
      color: #1d4ed8;
      background: #ffffff;
      border: 1.5px solid #93c5fd;
      border-radius: 6px;
      padding: 2px 10px;
      font-weight: 700;
      font-size: 20px;
      line-height: 1.1;
      animation: pulse-glow 3s ease-in-out infinite;
      cursor: help;
    }

    @keyframes pulse-glow {
      0%, 100% { box-shadow: 0 0 0 0 rgba(37,99,235,0); }
      50% { box-shadow: 0 0 0 4px rgba(37,99,235,0.22); }
    }

    .eq-caption {
      font-size: 0.82rem;
      color: #2563eb;
      font-weight: 600;
      display: flex;
      justify-content: center;
      align-items: center;
      gap: 6px;
      text-align: center;
      line-height: 1.35;
      padding: 0 4px;
    }

    .eq-caption-icon {
      font-size: 1rem;
      line-height: 1;
      flex-shrink: 0;
    }

    /* Visual Ratio Section */
    .bar-section {
      display: flex;
      flex-direction: column;
      gap: 6px;
    }

    .section-header {
      display: flex;
      justify-content: space-between;
      align-items: center;
      flex-wrap: wrap;
      gap: 6px 12px;
      padding-right: 42px; /* Leave space clear for the top badge indicator */
    }

    .section-title {
      font-size: 0.78rem;
      font-weight: 700;
      color: #475569;
      text-transform: uppercase;
      letter-spacing: 0.6px;
    }

    .section-subtitle {
      font-size: 0.75rem;
      color: #64748b;
      font-weight: 500;
      white-space: nowrap;
    }

    /* Proportional Bar Track */
    .bar-track-wrapper {
      position: relative;
      margin-top: 18px; /* Prevents badge from overlapping header */
    }

    .bar-track {
      width: 100%;
      height: 42px;
      border-radius: 8px;
      display: flex;
      overflow: visible;
      position: relative;
      background: #e2e8f0;
    }

    .bar-intact {
      width: 98.5%;
      background: linear-gradient(90deg, #2563eb, #3b82f6);
      border-top-left-radius: 8px;
      border-bottom-left-radius: 8px;
      display: flex;
      align-items: center;
      padding-left: 12px;
      color: #ffffff;
      font-weight: 600;
      font-size: 0.82rem;
      letter-spacing: 0.2px;
      white-space: nowrap;
      overflow: hidden;
      text-overflow: ellipsis;
      transition: opacity 0.35s ease;
      cursor: pointer;
    }

    .bar-ionized {
      width: 1.5%;
      min-width: 10px;
      background: #ef4444;
      border-top-right-radius: 8px;
      border-bottom-right-radius: 8px;
      position: relative;
      cursor: pointer;
      transition: opacity 0.35s ease;
    }

    /* Indicator marker for tiny sliver */
    .ionized-pointer {
      position: absolute;
      top: -21px;
      right: 0;
      transform: translateX(3px);
      display: flex;
      flex-direction: column;
      align-items: center;
      pointer-events: none;
      z-index: 2;
    }

    .pointer-tag {
      background: #b91c1c;
      color: #fff;
      font-size: 0.68rem;
      font-weight: 700;
      padding: 1px 6px;
      border-radius: 4px;
      white-space: nowrap;
      box-shadow: 0 1px 2px rgba(0,0,0,0.15);
    }

    .pointer-arrow {
      width: 0;
      height: 0;
      border-left: 4px solid transparent;
      border-right: 4px solid transparent;
      border-top: 4px solid #b91c1c;
    }

    /* Cards Grid */
    .detail-grid {
      display: grid;
      grid-template-columns: 1fr 1fr;
      gap: 10px;
      margin-top: 6px;
    }

    .detail-card {
      padding: 10px 12px;
      border-radius: 8px;
      display: flex;
      flex-direction: column;
      gap: 3px;
      transition: background-color 0.35s ease, box-shadow 0.35s ease, border-color 0.35s ease;
      cursor: default;
    }

    .detail-card.blue {
      background: #eff6ff;
      border-left: 4px solid #2563eb;
    }

    .detail-card.red {
      background: #fef2f2;
      border-left: 4px solid #ef4444;
    }

    .detail-card.blue:hover {
      background: #e0f2fe;
    }

    .detail-card.red:hover {
      background: #fee2e2;
    }

    .detail-header {
      display: flex;
      align-items: baseline;
      gap: 6px;
      flex-wrap: wrap;
    }

    .detail-card.blue .chem-formula { color: #1d4ed8; font-size: 1.02rem; }
    .detail-card.red .chem-formula { color: #b91c1c; font-size: 1.02rem; }

    .detail-count {
      font-size: 0.8rem;
      font-weight: 600;
      color: #334155;
    }

    .detail-badge {
      font-size: 0.73rem;
      font-weight: 700;
      text-transform: uppercase;
      letter-spacing: 0.4px;
      margin-top: 2px;
    }

    .badge-blue { color: #2563eb; }
    .badge-red { color: #dc2626; }

    /* Educational hint */
    .equilibrium-note {
      font-size: 0.75rem;
      color: #64748b;
      text-align: center;
      line-height: 1.35;
      padding-top: 4px;
    }

    @media (max-width: 420px) {
      body {
        padding: 8px 4px;
        gap: 12px;
      }
      .eq-display {
        font-size: 0.95rem;
        gap: 5px;
        padding: 8px 8px;
      }
      .chem-formula {
        font-size: 0.98rem;
      }
      .eq-symbol {
        font-size: 17px;
        padding: 2px 7px;
      }
      .detail-grid {
        grid-template-columns: 1fr;
        gap: 8px;
      }
      .bar-intact {
        font-size: 0.78rem;
        padding-left: 8px;
      }
    }
  </style>
</head>
<body>

  
  <div class="equation-section">
    <div class="eq-display" role="region" aria-label="Ethanoic acid ionization equilibrium equation">
      <span class="chem-formula">CH<sub>3</sub>COOH<span class="state">(aq)</span></span>
      <div class="eq-symbol-wrap">
        <span class="eq-symbol" title="Reversible dynamic equilibrium">⇌</span>
      </div>
      <span class="chem-formula">CH<sub>3</sub>COO<sup>−</sup><span class="state">(aq)</span></span>
      <span class="eq-plus">+</span>
      <span class="chem-formula">H<sup>+</sup><span class="state">(aq)</span></span>
    </div>
    <div class="eq-caption">
      <span class="eq-caption-icon" aria-hidden="true">⇄</span>
      <span>Forward and backward reactions occur simultaneously</span>
    </div>
  </div>

  
  <div class="bar-section">
    <div class="section-header">
      <span class="section-title">Composition in Water</span>
      <span class="section-subtitle">Per 100 dissolved molecules</span>
    </div>
    
    
    <div class="bar-track-wrapper">
      <div class="bar-track" role="img" aria-label="Visual ratio showing 99 percent intact molecules to 1 percent ions">
        <div class="bar-intact" title="99% Intact CH3COOH">
          <span>~99% Intact Molecules (CH<sub>3</sub>COOH)</span>
        </div>
        <div class="bar-ionized" title="~1% Ionised into H⁺ and CH₃COO⁻">
          <div class="ionized-pointer">
            <span class="pointer-tag">~1%</span>
            <span class="pointer-arrow"></span>
          </div>
        </div>
      </div>
    </div>

    
    <div class="detail-grid">
      <div class="detail-card blue">
        <div class="detail-header">
          <span class="chem-formula">CH<sub>3</sub>COOH</span>
        </div>
        <div class="detail-count">99 of 100 molecules</div>
        <div class="detail-badge badge-blue">Un-ionised (Intact)</div>
      </div>
      
      <div class="detail-card red">
        <div class="detail-header">
          <span class="chem-formula">H<sup>+</sup> + CH<sub>3</sub>COO<sup>−</sup></span>
        </div>
        <div class="detail-count">Only 1 of 100 molecules</div>
        <div class="detail-badge badge-red">Low H⁺ Concentration (Weak Acid)</div>
      </div>
    </div>

    <div class="equilibrium-note">
      Ethanoic acid only <strong>partially ionises</strong> in aqueous solution, resulting in a low concentration of hydrogen ions.
    </div>
  </div>

</body>
</html>

The reversible arrow ($\rightleftharpoons$) shows that ions continually recombine back into whole molecules, setting up a dynamic chemical equilibrium.

Common weak acids include ethanoic acid (vinegar), citric acid (citrus fruits), and carbonic acid (soda).

Can a weak acid ever be more dangerous than a strong acid?

A common mistake is confusing acid **strength** with **concentration** — they describe two completely different properties.

**Strength** is fixed by the chemical nature of the acid (the percentage that ionizes), whereas **concentration** is how many moles of acid are dissolved in a given volume of water.

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta name="aspect-ratio" content="1:1">
  <style>
    * {
      box-sizing: border-box;
      margin: 0;
      padding: 0;
    }

    body {
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
      background: transparent;
      color: #1e2945;
      padding: 8px;
      display: flex;
      flex-direction: column;
      gap: 8px;
      user-select: none;
    }

    /* Controls & Legend */
    .header-bar {
      display: flex;
      justify-content: space-between;
      align-items: center;
      flex-wrap: wrap;
      gap: 6px;
    }

    .legend {
      display: flex;
      align-items: center;
      gap: 10px;
      font-size: 13px;
      font-weight: 600;
    }

    .legend-item {
      display: flex;
      align-items: center;
      gap: 4px;
    }

    .btn-group {
      display: flex;
      gap: 4px;
      background: #e2e8f0;
      padding: 2px;
      border-radius: 6px;
    }

    .toggle-btn {
      border: none;
      background: transparent;
      padding: 4px 8px;
      font-size: 12px;
      font-weight: 600;
      border-radius: 4px;
      cursor: pointer;
      color: #475569;
      transition: background 0.2s, color 0.2s;
    }

    .toggle-btn.active {
      background: #ffffff;
      color: #0284c7;
      box-shadow: 0 1px 3px rgba(0, 0, 0, 0.1);
    }

    /* 2x2 Grid */
    .grid {
      display: grid;
      grid-template-columns: 1fr 1fr;
      grid-template-rows: 1fr 1fr;
      gap: 8px;
      width: 100%;
      aspect-ratio: 1 / 0.95;
    }

    .quadrant {
      background: #ffffff;
      border: 1.5px solid #e2e8f0;
      border-radius: 8px;
      padding: 6px;
      display: flex;
      flex-direction: column;
      position: relative;
    }

    .quadrant-title {
      font-size: 13px;
      font-weight: 700;
      text-align: center;
      padding-bottom: 4px;
      border-bottom: 1px solid #f1f5f9;
      color: #0f172a;
    }

    .beaker {
      flex: 1;
      position: relative;
      background: #f8fafc;
      border-radius: 6px;
      margin-top: 4px;
      overflow: hidden;
      border: 1px dashed #cbd5e1;
    }

    /* Particles */
    .particle {
      position: absolute;
      transform: translate(-50%, -50%);
      display: flex;
      align-items: center;
      justify-content: center;
      font-size: 11px;
      font-weight: 800;
      transition: opacity 0.3s ease, filter 0.3s ease;
    }

    /* H+ Ion (Red/Orange) */
    .ion-h {
      width: 22px;
      height: 22px;
      background: #ef4444;
      color: #ffffff;
      border-radius: 50%;
      box-shadow: 0 1px 2px rgba(239, 68, 68, 0.4);
      z-index: 2;
    }

    /* A- Anion (Cyan/Blue) */
    .ion-a {
      width: 24px;
      height: 24px;
      background: #0284c7;
      color: #ffffff;
      border-radius: 50%;
      box-shadow: 0 1px 2px rgba(2, 132, 199, 0.4);
    }

    /* HA Intact Molecule */
    .mol-ha {
      height: 24px;
      background: #64748b;
      border-radius: 12px;
      display: flex;
      align-items: center;
      padding: 0 2px;
      gap: 1px;
    }

    .mol-ha .part-h {
      width: 18px;
      height: 18px;
      background: #fca5a5;
      color: #7f1d1d;
      border-radius: 50%;
      display: flex;
      align-items: center;
      justify-content: center;
      font-size: 9px;
      font-weight: 800;
    }

    .mol-ha .part-a {
      width: 20px;
      height: 20px;
      background: #7dd3fc;
      color: #0c4a6e;
      border-radius: 50%;
      display: flex;
      align-items: center;
      justify-content: center;
      font-size: 10px;
      font-weight: 800;
    }

    /* Highlight Mode */
    .highlight-h .ion-a,
    .highlight-h .mol-ha {
      opacity: 0.2;
      filter: grayscale(80%);
    }

    .highlight-h .ion-h {
      transform: translate(-50%, -50%) scale(1.15);
      box-shadow: 0 0 8px rgba(239, 68, 68, 0.8);
    }

    /* Water tint indicator line */
    .water-line {
      position: absolute;
      bottom: 0;
      left: 0;
      right: 0;
      height: 85%;
      background: linear-gradient(180deg, rgba(224, 242, 254, 0.2) 0%, rgba(186, 230, 253, 0.35) 100%);
      pointer-events: none;
    }
  </style>
</head>
<body>

  <div class="header-bar">
    <div class="legend">
      <div class="legend-item">
        <div class="ion-h" style="width:16px;height:16px;font-size:9px;">H⁺</div>
      </div>
      <div class="legend-item">
        <div class="ion-a" style="width:16px;height:16px;font-size:9px;">A⁻</div>
      </div>
      <div class="legend-item">
        <div class="mol-ha" style="height:18px;">
          <div class="part-h" style="width:13px;height:13px;font-size:7px;">H</div>
          <div class="part-a" style="width:14px;height:14px;font-size:8px;">A</div>
        </div>
      </div>
    </div>

    <div class="btn-group">
      <button class="toggle-btn active" id="btnAll" onclick="setMode('all')">All</button>
      <button class="toggle-btn" id="btnH" onclick="setMode('h')">Highlight H⁺</button>
    </div>
  </div>

  <div class="grid" id="mainGrid">
    
    <div class="quadrant">
      <div class="quadrant-title">Concentrated Strong</div>
      <div class="beaker">
        <div class="water-line"></div>
        
        <div class="particle ion-h" style="top:25%; left:20%;">H⁺</div>
        <div class="particle ion-a" style="top:25%; left:45%;">A⁻</div>
        
        <div class="particle ion-h" style="top:26%; left:80%;">H⁺</div>
        <div class="particle ion-a" style="top:52%; left:75%;">A⁻</div>

        <div class="particle ion-h" style="top:52%; left:22%;">H⁺</div>
        <div class="particle ion-a" style="top:50%; left:50%;">A⁻</div>

        <div class="particle ion-h" style="top:78%; left:30%;">H⁺</div>
        <div class="particle ion-a" style="top:80%; left:60%;">A⁻</div>

        <div class="particle ion-h" style="top:42%; left:36%;">H⁺</div>
        <div class="particle ion-a" style="top:74%; left:85%;">A⁻</div>

        <div class="particle ion-h" style="top:70%; left:12%;">H⁺</div>
        <div class="particle ion-a" style="top:20%; left:65%;">A⁻</div>
      </div>
    </div>

    
    <div class="quadrant">
      <div class="quadrant-title">Dilute Strong</div>
      <div class="beaker">
        <div class="water-line"></div>
        
        <div class="particle ion-h" style="top:35%; left:30%;">H⁺</div>
        <div class="particle ion-a" style="top:40%; left:70%;">A⁻</div>

        <div class="particle ion-h" style="top:75%; left:65%;">H⁺</div>
        <div class="particle ion-a" style="top:70%; left:25%;">A⁻</div>
      </div>
    </div>

    
    <div class="quadrant">
      <div class="quadrant-title">Concentrated Weak</div>
      <div class="beaker">
        <div class="water-line"></div>
        
        <div class="particle ion-h" style="top:24%; left:25%;">H⁺</div>
        <div class="particle ion-a" style="top:32%; left:55%;">A⁻</div>

        <div class="particle mol-ha" style="top:24%; left:80%;">
          <div class="part-h">H</div><div class="part-a">A</div>
        </div>

        <div class="particle mol-ha" style="top:52%; left:28%;">
          <div class="part-h">H</div><div class="part-a">A</div>
        </div>

        <div class="particle mol-ha" style="top:54%; left:70%;">
          <div class="part-h">H</div><div class="part-a">A</div>
        </div>

        <div class="particle mol-ha" style="top:80%; left:35%;">
          <div class="part-h">H</div><div class="part-a">A</div>
        </div>

        <div class="particle mol-ha" style="top:78%; left:78%;">
          <div class="part-h">H</div><div class="part-a">A</div>
        </div>
      </div>
    </div>

    
    <div class="quadrant">
      <div class="quadrant-title">Dilute Weak</div>
      <div class="beaker">
        <div class="water-line"></div>
        
        <div class="particle mol-ha" style="top:38%; left:40%;">
          <div class="part-h">H</div><div class="part-a">A</div>
        </div>

        <div class="particle mol-ha" style="top:68%; left:65%;">
          <div class="part-h">H</div><div class="part-a">A</div>
        </div>
      </div>
    </div>
  </div>

  <script>
    function setMode(mode) {
      const grid = document.getElementById('mainGrid');
      const btnAll = document.getElementById('btnAll');
      const btnH = document.getElementById('btnH');

      if (mode === 'h') {
        grid.classList.add('highlight-h');
        btnH.classList.add('active');
        btnAll.classList.remove('active');
      } else {
        grid.classList.remove('highlight-h');
        btnAll.classList.add('active');
        btnH.classList.remove('active');
      }
    }
  </script>
</body>
</html>

A concentrated weak acid ($10\text{ mol/dm}^3$ ethanoic acid) has far more dissolved acid molecules than a dilute strong acid ($0.001\text{ mol/dm}^3$ hydrochloric acid), even though the strong acid ionizes completely.

Next time you look at an acid's formula and equation arrow, ask yourself: is it pushing $100\%$ forward ($\rightarrow$), or is it locked in a partial equilibrium ($\rightleftharpoons$)?

science

Acid Strength: Complete vs Partial Ionisation in Water. Define strong acids as completely ionised in aqueous solution and weak acids as only partially ionised.

Comparing Concentration with Strength (KS4 Chemistry)

GCSE Chemistry: Strong & Weak Acids (Higher Tier)

Chemical Misconceptions II: Acid Strength

To secure mastery for GCSE (Key Stage 4), explicitly decouple the colloquial use of 'strong/weak' (e.g. strong tea or coffee) from scientific terminology using a 2x2 conceptual matrix (Concentrated Strong, Dilute Strong, Concentrated Weak, Dilute Weak) with sub-microscopic particle drawings. Emphasise reaction notation (single arrow $\rightarrow$ vs dynamic equilibrium $\rightleftharpoons$) to reinforce that partial ionisation is a chemical equilibrium property, not an incomplete physical mixing.

Acid Strength: Complete vs Partial Ionisation in Water

Strong Acids: Complete Ionization