What are acid and base dissociation constants?
When an acid dissolves in water, it reacts according to the equation
HA + H₂O ⇌ H₃O⁺ + OH⁻
We can write an equilibrium constant expression
Since [H₂O] is a constant, we can write
We can define a new constant, the acid dissociation constant,
For a base, we can write the equilibrium reaction as
B + H₂O ⇌ BH⁺ + OH⁻
We can define the base dissociation constant,
Thus, the acid and base dissociation constants are the equilibrium constants without the term for the concentration of water.