Henderson-Hasselbalch Calculator
Calculate the pH of a buffer solution using the Henderson-Hasselbalch equation: pH = pKa + log₁₀([A⁻]/[HA]). Enter the pKa of your weak acid and the concentrations of the conjugate base and acid to determine pH, the base-to-acid ratio, and buffer effectiveness.
The Henderson-Hasselbalch equation is the cornerstone of buffer chemistry. It provides a direct relationship between pH, the pKa of a weak acid, and the ratio of conjugate base to acid concentrations in a buffer solution.
The Equation: pH = pKa + log₁₀([A⁻]/[HA])
Where [A⁻] is the molar concentration of the conjugate base and [HA] is the molar concentration of the weak acid. When [A⁻] = [HA], the ratio is 1, log(1) = 0, and pH = pKa. This is why buffers are most effective at pH values near the pKa.
Buffer Effectiveness:
A buffer is effective when the [A⁻]/[HA] ratio is between 0.1 and 10, corresponding to a pH range of pKa minus 1 to pKa plus 1. Outside this range, the buffer has insufficient capacity to resist pH changes. The total concentration of buffer components also matters: higher concentrations provide greater buffer capacity.
Common Buffer Systems:
- Acetic acid / Acetate (pKa = 4.76): useful for pH 3.8–5.8
- Phosphate (pKa2 = 7.20): useful for pH 6.2–8.2
- Tris (pKa = 8.07): useful for pH 7.1–9.1
- Bicarbonate (pKa = 6.35): physiological buffer system