Henderson-Hasselbalch Calculator – Buffer pH Made Easy

The Henderson-Hasselbalch equation calculates the pH of a buffer solution. A buffer resists pH changes when you add small amounts of acid or base. The equation relates pH to the pKa of the weak acid and the ratio of conjugate base to acid concentrations.

Henderson-Hasselbalch Equation

Where:

• pH = Acidity of the buffer solution
• pKa = Acid dissociation constant (negative log of Ka)
• [A⁻] = Concentration of conjugate base (mol/L)
• [HA] = Concentration of weak acid (mol/L)

Buffer Capacity

A buffer works best when pH equals pKa. At this point, [A⁻] = [HA] and the ratio equals 1. The log of 1 is 0, so pH = pKa. Buffers maintain effective pH control within ±1 pH unit of the pKa value.

Example Calculation

You prepare an acetate buffer with 0.1 M acetic acid (pKa = 4.76) and 0.1 M sodium acetate. The ratio [A⁻]/[HA] = 0.1/0.1 = 1. Since log(1) = 0, pH = 4.76 + 0 = 4.76.