HgS↓ + Na2S -> Na2[HgS2] — Redox Reactions and Volumetric Analysis Chemistry Question

💡 Solution & Explanation

Step 1: Identify starting materials: Mercuric sulfide (HgS↓) is an extremely insoluble black precipitate. Step 2: Observe reaction with concentrated sodium sulfide (Na2S): The sulfide ion acts as a strong ligand, coordinating with Hg2+ to form a soluble dithiomercurate(II) complex, [HgS2]2-. Step 3: Because the insoluble precipitate dissolves to form a clear solution of a soluble complex, this is classified as a precipitate dissolution reaction (type B).