Hydrolysis is the interaction of anion or cation of the salt with water to produce an acidic or basic solution. For example:
An aqueous solution of copper sulphate is acidic whereas the aqueous solution of the sodium acetate is basic in character. However, salts of strong acids and strong bases such as sodium chloride form neutral solution. This is due to the fact that a salt on dissolution in water undergoes dissociation to form ions. These ions can interact with water molecules and thereby produce either an acidic or an alkaline solution. This whole process is called hydrolysis.
Hydrolysis is reverse of neutralization. The pH of the solution gets affected by this interaction.
The equilibrium constant of hydrolysis reaction is called hydrolysis constant. The general hydrolysis equlibria and hydrolysis constants are given below:
Hydrolysis of anion (A–)
BA + H2O ————–> HA + BOH
A– + H2O ———-> HA + OH–
Kh = [HA] [OH–] / [A–]
Hydrolysis of cation
B+ + 2 H2O ————–> BOH + H3O+
Kh = [BOH] [H3O+] / [B+]
Hence, the fraction of the total salt that gets hydrolyzed at equilibrium is called degree of hydrolysis. It is denoted by h.
