Qualitative Analysis of Nickel (II) Ion

Take the original solution and add NH₄OH to make it alkaline. Pass hydrogen sulphide gas (H₂S) through the solution, a precipitate is obtained. Formation of black precipitate indicates the presence of Ni²⁺.

Ni²⁺ + S^2- → NiS

Confirmatory Test

Black precipitate of NiS is soluble in hot conc. HNO₃ giving light green solution. On adding NH₄OH and dimethylglyoxime reagent to the solution, a cherry red precipitate of nickel dimethylglyoxime is obtained.

3NiS + 2HNO₃ + 6H⁺ → 3Ni²⁺ + 2NO + 4H₂O + 3S ↓