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Buffer pH: Henderson–Hasselbalch

Estimate buffer pH from pKₐ and the concentrations of a conjugate acid–base pair.

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Understand the calculation

Formula and example

How it is calculated

pH ≈ pKₐ + log₁₀([A⁻]/[HA])

Worked example

With pKₐ = 4.76 and equal acid and base concentrations, the estimated pH is 4.76.

Things to check

  • The ratio describes the equilibrium pair; matching units cancel out.
  • The approximation requires a suitable buffer system. Very high dilution, high ionic strength and additional equilibria need a more detailed analysis.

Sources and references