Question

Explain about the hydrolysis of salt of strong base and weak acid. Derive the value of K_h for that reaction.

Answer 1

1. Coordination number: The number of nearest neighbours that surrounding a particle in a crystal is called the coordination number of that particle.

2. In aqueous solution, CH₃COONa is completely dissociated as follows

CH₃COONa_(aq) →  CH₃COO^-_(aq) + Na⁺_(aq)

3. CH₃COO^- is a conjugate base of the weak acid CHCOOH and it has a tendency to react with H⁺ from water to produce unionised acid. But there is no such tendency for Na⁺ to react with OH^-

4. CH₃COO^-_(aq) + H₂O_(I) \(\rightleftharpoons\) CH₃COOH_(aq) + OH^-_(aq) and therefore [OH^-] > [H⁺], such cases, the solution is basic due to the hydrolysis and pH is greater than 7.

5. Relationship between equilibrium constant, hydrolysis constant and the dissociation constant of acid is derived as follows:

K_h value in terms of degree of hydrolysis (h) and the concentration of salt (c) for the equilibrium can be obtained as in the case of Ostwald’s dilution law K_h = h²C and \([OH^-]=\sqrt{K_h.C}\)