Salt of Strong Acid and Strong Base

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Here, neither the cation nor the anion undergoes hydrolysis. Therefore, the resulting solution is neutral. For example, aqueous solution of KCl is neutral because when dissolved in water, its ions K⁺ and Cl^- have no tendency to react with the H⁺ and OH^- ions of water. The products of such a reaction are KOH and HCl, which are themselves completely dissociated. As a result, there is no change in the concentration of H⁺ and OH^- ions and hence the solution continues to remain neutral.

Hence, the salts of strong acids and strong bases do not undergo hydrolysis and the resulting solution is neutral.

Problem

13. The pH of a 0.1 M solution of NH₄Cl is 5.127 Calculate

(i) The hydrolysis constant.

(ii) The degree of hydrolysis

(iii) Dissociation constant of the base.

Solution

pH of the solution = 5.127

pH = - log[H⁺]

log [H⁺] = -pH = -5.127

[H⁺] = antilog (-5.127)

= 7.46 x 10^-6

The hydrolysis reaction is

If 'h' is the degree of hydrolysis, [H⁺] = ch = 7.46 x 10-6

= 7.46 x 10^-5

(ii) Hydrolysis constant, K_h = ch²

= 0.1 x (7.46 x 10^-5) ²

= 5.56 x 10^-10