The Henderson–Hasselbalch equation is a rule in chemistry that helps us find the pH of a solution made from a weak acid and its conjugate base (or a weak base and its conjugate acid).
It explains how the acidity of the solution depends on two things:
- The natural strength of the acid, expressed as its pKa value.
- The balance between the amount of acid present and the amount of its salt or base present.
This idea is very useful in buffer solutions, which are mixtures that keep the pH fairly steady even if small amounts of acid or base are added. It is widely used in biology, medicine, and chemistry—for example, to understand how blood maintains a nearly constant pH.