Henderson Hasselbalch Calculator

e.g., acetic acid pKa = 4.75; phosphate pKa2 = 7.2.
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Chemistry

Calculate the pH of a buffer solution using the Henderson-Hasselbalch equation.

Formula

pH = pKₐ + log₁₀([A⁻]/[HA])
  • Assumes dilute solution and ideal behavior.
  • Best buffer range: pKa ± 1 pH unit (ratio between 0.1 and 10).
  • At [A⁻]=[HA]: pH = pKa (maximum buffer capacity).
  • For physiological buffers: bicarbonate pKa = 6.1, phosphate pKa2 = 7.2.

Acetate buffer: pKa=4.75, equal concentrations

Inputs
  • pKₐ of Weak Acid: 4.75
  • [A⁻] Conjugate Base Concentration: 0.1 M
  • [HA] Weak Acid Concentration: 0.1 M

pH = 4.75 + log(0.1/0.1) = 4.75 + log(1) = 4.75 + 0 = 4.75.

Frequently asked questions

When is a buffer most effective?
When [A⁻]/[HA] ≈ 1, i.e., pH ≈ pKa. Maximum buffer capacity occurs at pH = pKa.
What is the Henderson-Hasselbalch equation used for?
Designing and analyzing buffer solutions in chemistry, biochemistry, and medicine.