A pale yellow inorganic compound K is insoluble in hot and dil. HNO3 but dissolves in concentrated a — Qualitative and Quantitative Analysis Chemistry Question
Question
A pale yellow inorganic compound K is insoluble in hot and dil. HNO3 but dissolves in concentrated ammonia solution and compound L is formed. On treatment with dil. HNO3 compound L produces a metal cation which gives white precipitate M with Hypo solution. When an aqueous solution of (M) is boiled, a black precipitate of (N) is formed which dissolves in hot dil. HNO3 and on adding HCl gives a white precipitate. When the compound (K) is heated with concentrated H2SO4 and MnO2 brown fumes are observed.
💡 Solution & Explanation
Step 1: When NaOH is added to the mixture containing Al3+, Zn2+, and Cu2+, all of them initially form hydroxide precipitates. Step 2: Since Al(OH)3 and Zn(OH)2 are amphoteric, they dissolve in excess NaOH to form soluble aluminate ([Al(OH)4]-) and zincate ([Zn(OH)4]2-) complexes. Step 3: In contrast, Cu(OH)2 is a basic hydroxide and remains insoluble as a characteristic blue precipitate, allowing both the identification and separation of Cu2+ in one step, matching option (c).