Buffer Preparation Calculator mechanism

Model scope

The core weak-acid/conjugate-base partitioning is standard, but the specification is not complete enough for an unambiguous production calculator. It must define the acid/base chemical forms, hydrate states, stock concentrations, final-volume procedure, and separate formulas and output labels for direct salt mixing versus titration with strong base. The fourth vector intentionally records the ambiguity: for the acid-plus-strong-base route with C_total=0.200 M and V=0.100 L, initial weak-acid moles are 0.0200 mol, final HA moles are 0.0066666667 mol, NaOH moles are 0.0133333333 mol, acid-stock volume is 20.0 mL, NaOH-stock volume is 6.6666667 mL, and makeup water is 73.3333333 mL.

• The Henderson-Hasselbalch equation correctly gives [A⁻]/[HA] = 10^(pH−pKa), and C_total = [HA]+[A⁻] correctly partitions total buffer concentration into the two equilibrium forms.
• For the acid-plus-strong-base option, the required stoichiometric reaction formula is missing: moles of strong base added must equal final moles of A⁻, while initial weak-acid moles equal total buffer moles.
• The stated mass=C·V·M formula is valid only when C is the component molarity, V is in liters, and M is in grams per mole. It is not sufficient to calculate stock-solution volumes without stock molarity or density.
• The formula does not specify the chemical forms whose molar masses are used, including hydrate state, salt counterion, or whether the acid and conjugate base are supplied as pure solids or solutions.
• Henderson-Hasselbalch is an approximation based on concentrations rather than activities and may be inaccurate at high ionic strength, extreme dilution, or when water autoionization is significant.

Units and conventions

• Concentrations are mol/L (M).
• Final volume is converted to liters before multiplying by molarity.
• Molar masses are in g/mol, producing masses in grams.
• Stock-solution volumes require stock concentrations in mol/L and are calculated as volume=moles/stock molarity.
• The specified pKa applies at the preparation temperature and to the exact acid/conjugate-base chemical forms selected.
• The target pH is interpreted as −log10(activity of H+), while the calculation approximates activities with concentrations.

Inspectable vector

One of 4 source-bound review vectors:

{
  "inputs": {
    "mode": "weak_acid_plus_conjugate_base",
    "target_pH": 4.76,
    "pKa": 4.76,
    "total_buffer_concentration_M": 0.1,
    "final_volume_L": 1,
    "weak_acid": "acetic acid",
    "conjugate_base": "sodium acetate, anhydrous",
    "weak_acid_molar_mass_g_per_mol": 60.05,
    "conjugate_base_molar_mass_g_per_mol": 82.03
  },
  "expected_outputs": {
    "weak_acid_moles": 0.05,
    "conjugate_base_moles": 0.05,
    "weak_acid_mass_g": 3.0025,
    "conjugate_base_mass_g": 4.1015
  },
  "working": "1. Ratio A⁻/HA = 10^(pH−pKa) = 10^(4.76−4.76) = 1. 2. [HA] = C_total/(1+ratio) = 0.100/(1+1) = 0.0500 M. 3. [A⁻] = 0.100−0.0500 = 0.0500 M. 4. n(HA) = 0.0500 mol/L × 1.000 L = 0.0500 mol. 5. n(A⁻) = 0.0500 mol/L × 1.000 L = 0.0500 mol. 6. m(HA) = 0.0500 mol × 60.05 g/mol = 3.0025 g. 7. m(A⁻) = 0.0500 mol × 82.03 g/mol = 4.1015 g."
}

Failure boundary

BREAK_CLAIMED · SELF_FLAGGED

The extreme pH input pH=-400 causes 10^-400 to underflow to zero in plain JavaScript arithmetic, silently eliminating the conjugate-base component instead of representing its mathematically nonzero amount. The convention probe also exposes a potentially catastrophic mL-versus-L interpretation error if units are not enforced.

Other records

Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

• VERIFIED_LEDGER.json
• evidence-tranche4/tranche4-results.json
• BOUNDARY_HAZARD_CATALOG.json