Salts hydrolyse when they contain the conjugate of a weak acid or weak base. Strong acid + strong base salt (NaCl): no hydrolysis, pH = 7. Weak acid + strong base salt (CH3COONa): the anion CH3COO- hydrolyses — CH3COO- + H2O <=> CH3COOH + OH-, making the solution basic. pH = 7 + $\frac{1}{2}$pKa + $\frac{1}{2}$log(C). Strong acid + weak base salt (NH4Cl): the cation NH4+ hydrolyses — NH4+ <=> NH3 + H+, making the solution acidic. pH = 7 - $\frac{1}{2}$pKb - $\frac{1}{2}$log(C). Weak acid + weak base salt (CH3COONH4): pH = 7 + $\frac{1}{2}$pKa - $\frac{1}{2}$pKb. pH is independent of concentration. If Ka > Kb, solution is acidic; if Kb > Ka, solution is basic; if Ka = Kb, solution is neutral.