Acid dissociation constant

In chemistry, an acid dissociation constant (also known as acidity constant, or acid-ionization constant; denoted ⁠ K a {\displaystyle K_{a}} ⁠) is a quantitative measure of the strength of an acid in solution. It is the equilibrium constant for a chemical reaction HA ↽ − − ⇀ A − + H + {\displaystyle {\ce {HA <=> A^- + H^+}}} known as dissociation in the context of acid–base reactions.