Henderson-Hasselbalch Calculator
Buffer pH, and where the buffer stops buffering.
Work out Henderson-Hasselbalch. Buffer pH, and where the buffer stops buffering. Free, with no account and nothing to download.
4.76 for acetic acid, 7.21 for the second proton of phosphoric acid.
Buffer pH
4.76
Ratio 1 : 1 · within useful range
pH = pKa + log([A⁻]/[HA]). At equal concentrations the log term vanishes and the pH is the pKa exactly — which is also where the buffer is strongest, because adding acid or base moves the ratio least. Beyond a 10:1 ratio in either direction the solution has effectively stopped buffering, so choose a weak acid whose pKa sits within one unit of the pH you need rather than adjusting the ratio to breaking point.
How the Henderson-Hasselbalch Calculator works
pH = pKa + log([A⁻]/[HA]). At equal concentrations the log term vanishes and the pH is the pKa exactly — which is also where the buffer is strongest, because adding acid or base moves the ratio least.
Also known as: buffer ph calculator · buffer solution calculator · henderson hasselbalch equation · how to calculate buffer ph
Frequently asked questions
What is the Henderson-Hasselbalch equation?
pH = pKa + log([conjugate base]/[weak acid]). At a 1:1 ratio the pH equals the pKa.
What is the useful buffer range?
Roughly one pH unit either side of the pKa, corresponding to ratios from 1:10 to 10:1. Beyond that the solution has effectively stopped buffering.
How do I choose a buffer?
Pick a weak acid whose pKa is within one unit of the pH you need, rather than pushing an unsuitable one to an extreme ratio.
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