How this calculator works
The mixture mode first totals acid and base formula units. For known strengths it solves charge balance with water ionization and the selected weak equilibria. A diprotic weak acid includes both dissociation constants; its complete equivalence consumes two hydroxide equivalents per formula unit. Inverse concentration and volume modes impose complete stoichiometric equivalence. Unknown strengths still permit amount and equivalent balances, but no pH. The model assumes ideal dilute solutions and additive volumes, without precipitation, complex formation or volatile losses.
Formula
At equivalence: acid H+ count x acid concentration x acid volume = base OH- count x base concentration x base volume. Mixture pH follows electroneutrality and Ka/Kb equilibria, with [H+][OH-] = Kw.
Worked example
Mixing 25 mL of 0.1 mol/L strong acid with 25 mL of 0.1 mol/L strong base gives pH 7 at pKw 14. Adding 37.5 mL base leaves 0.00125 mol OH- in 62.5 mL, giving pH about 12.30103.
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Frequently asked questions
Is equivalence always at pH 7?
Only an ideal strong-acid/strong-base system has neutral pH at equivalence. Weak conjugate species can hydrolyse.
Can weak acid and weak base both be selected?
Yes. The ideal equilibrium charge balance includes both conjugate pairs.
What does unknown strength return?
Amounts, the stoichiometric state and complete-equivalence volume. It omits pH because a dissociation model is missing.