Two types of ions hydrolyze in aqueous : (1) the salts of weak and (2) certain metal ions.

Hydrolysis of an ion is its reaction with water to produce an acidic or basic solution.

(1) Sodium acetate is a salt of the weak acid acetic acid. Acetate ion is the conjugate base of acetic acid. It hydrolyzes in water to form a basic solution:

CH?COO?(aq) + H?O(l) ? CH?COOH(aq) + OH?(aq)

Ammonium chloride is a salt of the weak base ammonia. Ammonium ion is the conjugate acid of the weak base ammonia. It hydrolyzes in water to form an acidic solution:

NH??(aq) + H?O(l) ? NH?(aq) + H?O?(aq)

(2) Metal ions are Lewis acids. In solution, they form aqua ions with the general formula ##M(H?O)_n^(m+)##. Examples are ##Be(H?O)_4^(2+)##, ##Al(H?O)_6^(3+)##, and ##Fe(H?O)_6^(3+)##. Small metal ions with high charge densities undergo hydrolysis to form acidic solutions. For example,

##Al(H?O)_6^(3+) + H_2O ? Al(H?O)_5(OH)^(2+) + H_3O^+##