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    "Activity coefficients ≈ 1",
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    "Not pH = −log10[H+]",
    "Not polyprotic"
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    "Monoprotic buffer pair as given — not ICE equilibrium",
    "Not pH = −log10[H+]",
    "Not activity coefficients or polyprotic"
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    "HA ≤ 0 or A ≤ 0 → VALUE_MUST_BE_POSITIVE",
    "Ka ≤ 0 → VALUE_MUST_BE_POSITIVE"
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      "section": "Henderson–Hasselbalch equation",
      "url": "https://openstax.org/books/chemistry-2e/pages/14-6-buffers",
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      "section": "conjugate acid–base pair",
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        "Ka": 0.000009999999999999999,
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        "A": 0.2,
        "ratio": 2,
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        "Ka": 0.000009999999999999999,
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        "A": 0.1,
        "ratio": 1,
        "model": "henderson_hasselbalch"
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        "HA": 0.1,
        "A": 0.2
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        "Ka": 0.00001,
        "HA": 0.1,
        "A": 0.2,
        "ratio": 2,
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      "id": "boundary-hh-missing",
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        "HA": 0.1
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      "expectError": "MISSING_REQUIRED_INPUT",
      "code": "MISSING_REQUIRED_INPUT",
      "error": "A is required"
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      "id": "boundary-hh-ha",
      "ok": true,
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      "inputs": {
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        "HA": 0,
        "A": 0.1
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      "code": "VALUE_MUST_BE_POSITIVE",
      "error": "HA must be greater than zero"
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        "Ka": 0.00001,
        "HA": 0.1,
        "A": 0.1
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      "expectError": "MIXED_INPUT_ENCODING",
      "code": "MIXED_INPUT_ENCODING",
      "error": "Use pKa or Ka, not both encodings"
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    {
      "id": "property-hh-ph",
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      "kind": "property",
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