Question

Give one example each of a salt which gives an aqueous solution having:
(a) pH less than 7
(b) pH equal to 7
(c) pH more than 7

Answer 1

a) NH₄Cl is formed from a weak base, ammonium hydroxide (NH₄OH), and a strong acid, hydrochloric acid (HCl). On hydrolysis, NH₄Cl forms more H⁺ ions than OH^- ions. Thus, it is acidic, with a pH less than 7.

b) KCl is formed from a strong acid, hydrochloric acid (HCl), and a strong base, potassium hydroxide (KOH). Thus, KCl, on hydrolysis, forms equal amounts of H⁺ and OH^- ions. Therefore, an aqueous solution of KCl is neutral, with a pH of almost 7.

c) K₂CO₃ is formed from a weak acid, carbonic acid (H₂CO₃), and a strong base, potassium hydroxide (KOH). On hydrolysis, K₂CO₃ forms more OH^- ions than H⁺ ions. Thus, it is basic, with a pH more than 7.