. Salt Hydrolysis When an acid reacts with a base, a salt and water are formed and the reaction is called neutralization. Salts completely dissociate in aqueous solutions to give their constituent ions. The ions so produced are hydrated in water.
In certain cases, the cation, anion or both react with water and the reaction is called salt hydrolysis. Hence, salt hydrolysis is the reverse of neutralization reaction. . .
Salts of strong acid and a strong base Let us consider the reaction between NaOH and nitric acid to give sodium nitrate and water. NaOH(aq)+HNO (aq) NaNO (aq)+H O(l) The salt NaNO completely dissociates in water to produce Na + and NO − ions. NaNO (aq) Na (aq)+NO (aq) Water dissociates to a small extent as H O(l) H (aq)+OH (aq) Since [H ]=[OH ], water is neutral NO - ion is the conjugate base of the strong acid HNO and hence it has no tendency to react with H + . Similarly, Na + is the conjugate acid of the strong base NaOH and it has no tendency to react with OH - .
It means that there is no hydrolysis. In such cases [H ]=[OH ] - pH is maintained and, therefore, the solution is neutral. . .
Hydrolysis of Salt of strong base and weak acid (Anionic Hydrolysis). Let us consider the reactions between sodium hydroxide and acetic acid to give sodium acetate and water. NaOH (aq) + CH COOH(aq) CH COONa(aq)+H O(l) In aqueous solution, CH COONa is completely dissociated as below CH COONa (aq) CH COO (aq)+Na (aq) → CH COO is a conjugate base of the weak acid CH COOH and it has a tendency to react with H + from water to produce unionised acid There is no such tendency for Na + to react with OH - . CH COO (aq) + H O(l) CH COOH (aq) + OH (aq) and therefore [OH ]>[H ] + , in such cases, the solution is basic due to hydrolysis and the pH is greater than .