When ionic compounds dissolve to produce ions the process is typically called dissociation.
Dissociation of ionic compounds occurs when water molecules “pull apart” the ionic crystal. This occurs due to strong attractions between the polar ends of the water molecule and the positive and negative ions within the crystal.
An acid dissociation constant, Ka, (also known as acidity constant, or acid-ionization constant) is a quantitative measure of the strength of an acid in solution. It is the equilibrium constant for a chemical reaction known as dissociation in the context of acid–base reactions.
A similar equilibrium exists when a weak base is dissolved in water. The base will accept a proton from water and form a conjugate acid. This equilibrium has its own special constant, Kb, known as the base dissociation constant. Like the acid dissociation constant, it is defined as the equilibrium constant multiplied by the concentration of water.