Question

$NH_4OH$ is a weak base but it becomes still weakerin the aqueous solution of

• A. $0.1\, M HCl$
• B. $0.1 \, M NH_4Cl$
• C. $0.1\, M H_2SO_4$
• D. $0.1\, M CH_3COOH$

Answer 1

Answer: (B)

$0.1 \, M NH_4Cl$

Answer 2

Common ion effect is observed when a solution of weak electrolyte is mixed with a solution of strong electrolyte which provides an ion common to that provided by a weak electrolyte. Ammonium hydroxide is a weak electrolyte and ammonium chloride is a strong electrolyte. Ammonium chloride provides ammonium ion which is common to that provided by ammonium hydroxide. Thus the pair $NH _{4} OH + NH _{4} Cl$ shows common ion effect. Ammonium chloride suppresses the ionization of ammonium hydroxide. Hence, ammonium hydroxide becomes still weaker in the presence of an aqueous solution of ammonium chloride.