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: The reaction of bismuth(III) ions with iodide ions (I-) initially forms a dark brown/black precipitate of bismuth(III) iodide (BiI3). Step 2: The black BiI3 precipitate reacts with excess iodide ions to form a highly stable, soluble tetraiodobismuthate(III) complex anion: BiI3 + I- -> [BiI4]-. Step 3: The [BiI4]- complex solution exhibits a characteristic orange/yellow-orange color. This confirms the presence of Bi3+, matching option (b).