Hydrolysis constant

A hydrolysis constant is an equilibrium constant for a hydrolysis reaction.

For example, if a metal salt such as AlCl3 dissolves in an aqueous solution, the metal cation behaves as a Lewis acid and hydrolyzes the water molecules in the solvent.
 * Al3+ + 2H2O &rarr; AlOH2+ + H3O+

The hydrolysis constant for this reaction is:
 * Khydrolysis = [H3O+] * [AlOH2+] / [Al3+]

In a more generalized form, the hydrolysis constant can be described as:
 * Ka = [H3O+] * [A-] / [HA]

where A- represents any base, and HA represents any acid.