Calculator
Buffer pH (Henderson-Hasselbalch)
Calculate the pH of a buffer from pKa and the ratio of conjugate base to acid concentrations.
pH
7.40
FAQ
What is the Henderson-Hasselbalch equation?
pH = pKa + log10([A⁻]/[HA]). It relates buffer pH to the pKa of the weak acid and the ratio of conjugate base to acid concentrations.
When does Henderson-Hasselbalch break down?
At very high or very low ratios of base to acid (typically beyond ±1 pH unit from the pKa) and at extreme concentrations or ionic strengths, the simple equation deviates from reality.
How do I prepare a buffer at a target pH?
Pick a buffer whose pKa is within ±1 unit of your target pH (e.g. Tris pKa 8.1, HEPES pKa 7.5, PIPES pKa 6.8), then adjust the base/acid ratio per Henderson-Hasselbalch.