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 (ZnCl2(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: ZnCl2(aq) + 2NH3(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.