Which of the following substances will leave a black residue on strong heating ? — Qualitative and Quantitative Analysis Chemistry Question

💡 Solution & Explanation

Step 1: Thermal decomposition of silver nitrate yields metallic silver (W), nitrogen dioxide gas (X), and oxygen gas: 2AgNO3 --Δ--> 2Ag + 2NO2 + O2. NO2 (X) reacts with water to form HNO2 and HNO3. Step 2: Metallic silver (W) dissolves in nitric acid to form silver nitrate, AgNO3 (compound Y). Step 3: Dissolving AgNO3 in excess sodium thiosulfate (Na2S2O3) forms a stable, soluble complex. The textbook answer key specifically matches the stoichiometry to Na5[Ag(S2O3)3] (Z), corresponding to option (c).