Which of the following salts on hydrolysis would give an alkaline solution?

Analyze the question: We need the salt whose aqueous solution is alkaline (pH > 7) after hydrolysis.

Concept: Salt hydrolysis depends on the strength of the acid and base that formed the salt:

• Strong acid + weak base gives an acidic solution.
• Weak acid + strong base gives an alkaline solution.
• Strong acid + strong base gives a neutral solution.

Solution:

• A. NH₄Cl: formed from HCl (strong acid) and NH₃ (weak base). NH₄⁺ + H₂O ⇌ NH₃ + H₃O⁺, so the solution is acidic.
• B. AlCl₃: formed from HCl (strong acid) and Al(OH)₃ (weak base). Al³⁺ hydrolyses to give H⁺, so the solution is acidic.
• C. CH₃COONa: formed from CH₃COOH (weak acid) and NaOH (strong base). The acetate ion hydrolyses: CH₃COO⁻ + H₂O ⇌ CH₃COOH + OH⁻ The OH⁻ produced makes the solution alkaline.
• D. NH₄NO₃: formed from HNO₃ (strong acid) and NH₃ (weak base), so the solution is acidic.

Sodium ethanoate (sodium acetate) gives an alkaline solution.

Tip: Remember "the stronger parent wins." The strong parent decides the nature of the solution. Strong base (NaOH) with weak acid gives alkaline. Strong acid with weak base gives acidic. Also, salts of sodium or potassium with a weak acid, like carbonates, ethanoates and cyanides, are typically alkaline.