Last updated: March 2, 2026

Understanding Buffer Solutions and the Henderson-Hasselbalch Equation

Formula

A buffer solution resists changes in pH when small amounts of acid or base are added. It consists of a weak acid and its conjugate base (or a weak base and its conjugate acid) in roughly equal concentrations.

The Henderson-Hasselbalch equation pH = pKa + log([A⁻]/[HA]) predicts the pH of a buffer. Buffers work best when the pH is within one unit of the pKa, where buffer capacity is highest.

Common use cases:

  • Biological pH maintenance
  • Laboratory solution preparation
  • Pharmaceutical formulation

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