What ions hydrolyze in aqueous solutions?

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:

CH₃COO⁻(aq) + H₂O(l) ⇌ CH₃COOH(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:

NH₄⁺(aq) + H₂O(l) ⇌ NH₃(aq) + H₃O⁺(aq)

(2) Metal ions are Lewis acids. In solution, they form aqua ions with the general formula ##M(H₂O)_n^(m+)##. Examples are ##Be(H₂O)_4^(2+)##, ##Al(H₂O)_6^(3+)##, and ##Fe(H₂O)_6^(3+)##. Small metal ions with high charge densities undergo hydrolysis to form acidic solutions. For example,

##Al(H₂O)_6^(3+) + H_2O ⇌ Al(H₂O)_5(OH)^(2+) + H_3O^+##