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: Separation of iron(III) hydroxide from aluminium hydroxide relies on their difference in amphoteric character. Step 2: Al(OH)3 is amphoteric and dissolves in excess sodium hydroxide (NaOH) to form soluble sodium aluminate (Na[Al(OH)4]), whereas Fe(OH)3 is purely basic and remains insoluble. Step 3: Therefore, adding NaOH solution successfully separates them by dissolving only Al(OH)3, leaving Fe(OH)3 as a precipitate, which matches option (c).