Which of the following mixtures can be separated by using excess NH3 solution? — Qualitative and Quantitative Analysis Chemistry Question

💡 Solution & Explanation

Step 1: Adding excess ammonia solution to Al^3+ forms a white gelatinous precipitate of Al(OH)3, which is completely insoluble in excess ammonia because Al^3+ does not form stable ammine complexes. Step 2: In contrast, Zn^2+ initially precipitates as Zn(OH)2 but then readily dissolves in excess ammonia to form the stable, soluble tetraamminezinc(II) complex: Zn(OH)2 + 4 NH3 ---> [Zn(NH3)4]^2+ + 2 OH^-. Step 3: This clear difference in solubility allows the complete separation of Al^3+ (as solid precipitate) from Zn^2+ (in solution), corresponding to option (b).