Henderson-Hasselbalch equation
A foundational equation in biochemistry and analytical chemistry for calculating buffer pH or required concentration ratios:
pH = pKa + log([A⁻] / [HA])
Rearranged to find the required ratio: [A⁻]/[HA] = 10^(pH − pKa)
Buffer design recipe
To make a buffer at a specific pH:
- Choose an acid with pKa within ±1 of target pH
- Calculate [A⁻]/[HA] ratio using this calculator
- Mix acid and conjugate base in that molar ratio
- Adjust pH to target with small amounts of strong acid/base