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Buffer pH Calculator

Calculate approximate buffer pH from pKa and weak-acid and conjugate-base concentrations using the Henderson–Hasselbalch equation. See the model assumptions.

Use this result well

Inputs that matter
Acid pKa, Weak acid [HA], Conjugate base [A⁻]
Output to expect
Approximate buffer pH
  • Check the units and required inputs before comparing results.
  • Keep the assumptions with a copied result so you can reproduce the calculation later.
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Reference & details

How it works

Use a dimensionless concentration ratio

Divide conjugate-base concentration by weak-acid concentration, using mol/L for both. Add its base-10 logarithm to the entered pKa.

pH ≈ pKa + log₁₀([A⁻]/[HA])

Source: OpenStax Chemistry 2e: Buffers

Read the model with its assumptions

This is a concentration approximation for a specified buffer pair, not a full equilibrium solver. The tool does not validate the solution conditions or measure a food sample.

Keep every input visible

The result retains pKa, each concentration and the logarithmic contribution. Calculations use logarithms of the two concentrations separately to avoid an overflowing intermediate ratio.

Updated: September 2026

Example Scenarios

Enter pKa 4.76, acid 0.01 mol/L and base 0.001 mol/L.

→ Approximate pH 3.76.

Keep pKa 4.76 and enter 0.01 mol/L for each species.

→ Approximate pH 4.76.

With pKa 4.76 and base 0.001 mol/L, change acid from 0.01 to 0.1 mol/L.

→ The modeled pH changes from 3.76 to 2.76; suitability of the approximation still needs assessment.

Common Mistakes to Avoid

Entering stock concentrations before mixing

Use the concentrations of the specified acid and base in the same final buffer.

Treating the output as measured food pH

A real food has ingredients and interactions outside this single-pair model. Use appropriate physical measurement for a food sample.

FAQ

Both fields use mol/L. They must refer to the same final solution.

Yes. With pKa and base held constant, increasing acid tenfold lowers the calculated pH by one unit.

Multiplying both concentrations by the same positive factor leaves their ratio unchanged in this model. This does not mean all physical solution properties stay the same.

No. Both concentrations must be positive; this calculator is not a weak-acid-only dissociation solver.

No. The result is a model calculation, not a food measurement or processing instruction.

About Buffer pH Calculator

Explore how the acid-to-base balance affects one specified buffer pair. Both concentration inputs refer to the same final solution and participate in the calculation.