When aqueous ammonia is added to one of the following solutions,a white precipitate which dissolved in excess ammonia is formed Identify the solution.

Answer Details

The solution that forms a white precipitate when aqueous ammonia is added, which dissolves in excess ammonia, is the solution of zinc chloride (ZnCl_2(aq)). The addition of aqueous ammonia to zinc chloride solution forms a white precipitate of zinc hydroxide (Zn(OH)_2(s)), which dissolves in excess ammonia to form a colorless, complex ion called tetraamminezinc(II) (Zn(NH₃)₄²⁺). This reaction can be represented by the following equation: ZnCl_2(aq) + 2NH_3(aq) + H₂O(l) → Zn(OH)_2(s) + 2NH₄Cl(aq) The formation of a white precipitate that dissolves in excess ammonia indicates the presence of a metal cation that can form a complex ion with ammonia. Zinc ions (Zn²⁺) have a small size and high charge density, making them highly polarizing and able to form complex ions with ammonia. In contrast, lead ions (Pb²⁺), copper ions (Cu²⁺), and iron ions (Fe²⁺) can also form white precipitates with aqueous ammonia, but these precipitates do not dissolve in excess ammonia due to the formation of insoluble hydroxides.