An unknown mixture contains one or two of the following : CaCO3, BaCl2, AgNO3, Na2SO4, ZnSO4 and NaO — Qualitative and Quantitative Analysis Chemistry Question
Question
An unknown mixture contains one or two of the following : CaCO3, BaCl2, AgNO3, Na2SO4, ZnSO4 and NaOH. The mixture is completely soluble in water and solution gives pink colour with phenolphthalein. When dilute hydrochloric acid is gradually added to the solution, a precipitate is formed which dissolves with further addition of the acid.
💡 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).