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Henderson-Hasselbalch Equation

The Henderson-Hasselbalch equation is a mathematical relationship that links the pH of a buffer solution to the concentrations of its acid and conjugate base.

The Equation​

  • Formula:
    pH = pKa + log([A⁻]/[HA])
    • [A⁻] = concentration of the conjugate base
    • [HA] = concentration of the weak acid
    • pKa = acid dissociation constant

Key Concepts​

  • When [A⁻] = [HA], pH = pKa
  • Can calculate pH of a buffer, required component ratio, or component concentrations
  • Useful for designing buffer solutions

Example​

  • Acetic acid (CH₃COOH) and acetate (CH₃COO⁻) buffer
    • [A⁻] = 0.25 M, [HA] = 0.25 M
    • pKa = 4.76
    • pH = 4.76 + log(0.25/0.25) = 4.76

Importance​

  • Helps in biochemical systems, like maintaining blood pH
  • Guides laboratory buffer preparation
  • Predicts pH changes when acid or base is added to a buffer

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