Equilibrium — how an acetate buffer resists pH change
An equimolar ethanoic acid / ethanoate buffer at pH 4.76: the reserves that mop up added acid and added base, Henderson–Hasselbalch, where the capacity is greatest, the working range, and what happens once the reserve runs out.
Rendering…
Make it your own.
{
"nodes": [
{ "id": "recipe", "type": "flask", "label": "0.10 M CH₃COOH + 0.10 M CH₃COO⁻", "x": 40, "y": 40, "width": 150, "height": 104, "fill": "#dbeafe", "stroke": "#1d4ed8", "bold": true },
{ "id": "ha", "type": "hexagon", "label": "Weak acid CH₃COOH reserve", "x": 215, "y": 40, "width": 150, "height": 104, "fill": "#dbeafe", "stroke": "#1d4ed8" },
{ "id": "eq", "type": "rounded", "label": "CH₃COOH ⇌ H⁺ + CH₃COO⁻", "x": 390, "y": 40, "width": 150, "height": 104, "fill": "#fef3c7", "stroke": "#a16207", "bold": true },
{ "id": "hh", "type": "clipboard", "label": "pH = pKa + log([A⁻]/[HA]) = 4.76", "x": 565, "y": 40, "width": 150, "height": 104, "fill": "#e0f2fe", "stroke": "#0369a1", "bold": true },
{ "id": "pick", "type": "target", "label": "Pick a pKa near the target pH", "x": 740, "y": 40, "width": 150, "height": 104, "fill": "#f1f5f9", "stroke": "#475569" },
{ "id": "a", "type": "hexagon", "label": "Conjugate base CH₃COO⁻ reserve", "x": 215, "y": 200, "width": 150, "height": 104, "fill": "#dbeafe", "stroke": "#1d4ed8" },
{ "id": "ka", "type": "clipboard", "label": "Ka = 1.75 × 10⁻⁵ ⇒ pKa = 4.76", "x": 390, "y": 200, "width": 150, "height": 104, "fill": "#f1f5f9", "stroke": "#475569" },
{ "id": "addacid", "type": "syringe", "label": "Add strong acid — H₃O⁺", "x": 40, "y": 360, "width": 150, "height": 104, "fill": "#fee2e2", "stroke": "#b91c1c", "bold": true },
{ "id": "moph", "type": "rounded", "label": "CH₃COO⁻ + H₃O⁺ → CH₃COOH + H₂O", "x": 215, "y": 360, "width": 150, "height": 104, "fill": "#dcfce7", "stroke": "#15803d" },
{ "id": "small", "type": "gauge-chart", "label": "Ratio shifts, pH barely moves", "x": 390, "y": 360, "width": 150, "height": 104, "fill": "#dcfce7", "stroke": "#15803d", "bold": true },
{ "id": "capacity", "type": "bar-chart", "label": "Capacity peaks when [A⁻] = [HA]", "x": 565, "y": 360, "width": 150, "height": 104, "fill": "#e0f2fe", "stroke": "#0369a1", "bold": true },
{ "id": "broken", "type": "cross", "label": "Reserve exhausted ⇒ pH crashes", "x": 740, "y": 360, "width": 150, "height": 104, "fill": "#fee2e2", "stroke": "#b91c1c", "bold": true },
{ "id": "addbase", "type": "syringe", "label": "Add strong base — OH⁻", "x": 40, "y": 520, "width": 150, "height": 104, "fill": "#fee2e2", "stroke": "#b91c1c", "bold": true },
{ "id": "mopoh", "type": "rounded", "label": "CH₃COOH + OH⁻ → CH₃COO⁻ + H₂O", "x": 215, "y": 520, "width": 150, "height": 104, "fill": "#dcfce7", "stroke": "#15803d" },
{ "id": "dilute", "type": "water-drop", "label": "Dilution: pH holds, capacity falls", "x": 390, "y": 520, "width": 150, "height": 104, "fill": "#ede9fe", "stroke": "#6d28d9" },
{ "id": "range", "type": "line-chart", "label": "Working range pKa ± 1 → 3.8–5.8", "x": 565, "y": 520, "width": 150, "height": 104, "fill": "#e0f2fe", "stroke": "#0369a1" }
],
"edges": [
{ "id": "e1", "source": "recipe", "target": "ha", "thickness": 2.5 },
{ "id": "e2", "source": "recipe", "target": "a", "thickness": 2.5 },
{ "id": "e3", "source": "ha", "target": "eq" },
{ "id": "e4", "source": "a", "target": "eq" },
{ "id": "e5", "source": "eq", "target": "ka", "label": "position set by Ka", "style": "dashed" },
{ "id": "e6", "source": "ka", "target": "hh", "label": "rearranged", "style": "dashed" },
{ "id": "e7", "source": "eq", "target": "hh", "thickness": 2.5 },
{ "id": "e8", "source": "addacid", "target": "moph", "thickness": 2.5 },
{ "id": "e9", "source": "a", "target": "moph", "label": "the base reserve acts", "style": "dashed" },
{ "id": "e10", "source": "addbase", "target": "mopoh", "thickness": 2.5 },
{ "id": "e11", "source": "ha", "target": "mopoh", "label": "the acid reserve acts", "style": "dashed" },
{ "id": "e12", "source": "moph", "target": "small", "thickness": 2.5 },
{ "id": "e13", "source": "mopoh", "target": "small", "thickness": 2.5 },
{ "id": "e14", "source": "small", "target": "capacity" },
{ "id": "e15", "source": "capacity", "target": "range", "style": "dashed" },
{ "id": "e16", "source": "capacity", "target": "broken", "label": "past the reserve", "style": "dashed" },
{ "id": "e17", "source": "dilute", "target": "capacity", "style": "dashed" },
{ "id": "e18", "source": "hh", "target": "pick", "label": "design rule", "style": "dashed" }
]
}