Which of the following mixtures of ions can be separated by using an excess of an NaOH solution? — Qualitative and Quantitative Analysis Chemistry Question

💡 Solution & Explanation

Step 1: Calcium carbonate (CaCO3, 'X') decomposes upon heating to form calcium oxide residue ('Y') and carbon dioxide gas: CaCO3 --Δ--> CaO + CO2. Step 2: Dissolving CaO ('Y') in water yields limewater, Ca(OH)2. Passing excess CO2 through Ca(OH)2 forms soluble calcium bicarbonate, Ca(HCO3)2 ('Z'): Ca(OH)2 + 2CO2 -> Ca(HCO3)2. Step 3: Heating Ca(HCO3)2 ('Z') decomposes it back into calcium carbonate (CaCO3, 'X'), water, and CO2. Therefore, compound 'X' is CaCO3, matching option (d).