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Chemistry

Buffer pH Calculator

Estimate buffer pH from pKa and the concentrations of a weak acid and its conjugate base.

Explicit units and model assumptionsLocal calculations with worked examples
Chemistry workspace
Chemistry workspace

Check the units, concentration basis and assumptions before interpreting the result.

See the method

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Your chemistry result

Your result

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Use the Calculate button to see your result.

Review the method below for assumptions and conventions.

How to use this tool

  1. Enter acid pka, weak acid concentration, conjugate base concentration.
  2. Select Calculate to view the result.
  3. Check the method and assumptions below before using the result.

The method, explained

Henderson–Hasselbalch estimate: pH = pKa + log10([conjugate base]/[weak acid]).

A WORKED EXAMPLE

Using acid pka = 4.76, weak acid concentration = 0.1 mol/L, conjugate base concentration = 0.1 mol/L, the result is 4.76 pH. Change these example inputs to match your task; use the method above to check each step.

Understanding your result

The ratio is one and log10(1) is zero, so the estimated pH equals pKa.

What to keep in mind

Uses concentration ratios as approximations to activities. Does not model added strong acid/base, dilution equilibria or buffer capacity. Educational calculation only; use validated procedures for laboratory work.

Reference: OpenStax Chemistry 2e — chemical quantities and models

Common questions

What happens when acid and base concentrations are equal?

The ratio is one and log10(1) is zero, so the estimated pH equals pKa.

Are my inputs uploaded?

No. This calculation runs in your browser without an account or an external API.

Methodology maintained by ClarityKit. How these tools are built and checked.