pH of Buffer Solution (Henderson-Hasselbalch)

Summary

Enter pKa and the moles (or concentrations) of conjugate base and weak acid to calculate buffer pH with a full step-by-step solution.

How it works

1. Enter the pKa of the weak acid (e.g., 4.74 for acetic acid, 6.35 for carbonic acid H₂CO₃).
2. Choose whether you are entering molar concentrations (mol/L) or mole amounts (mol) — the ratio is the same either way.
3. Enter the amount of conjugate base [A⁻] and weak acid [HA].
4. Click Calculate to see the buffer pH plus a line-by-line solution panel.
5. The solution shows: the [A⁻]/[HA] ratio, log₁₀ of that ratio, and the final pH = pKa + log([A⁻]/[HA]).
6. Adjust any input and the result updates instantly — no page reload needed.

Use cases

• Verify homework problems on buffer pH calculations.
• Prepare lab buffers by confirming the expected pH before mixing.
• Understand how changing the base-to-acid ratio shifts pH up or down.
• Teach or learn the Henderson-Hasselbalch equation step by step.
• Check buffer calculations for acetate, phosphate, carbonate, or custom acid systems.
• Convert mole amounts to a pH without manually computing logarithms.

Frequently Asked Questions