Q1(g). Gravimetric estimation of nickel in steel

Answer in brief

Nickel is precipitated from a hot, just ammoniacal tartrate solution as red nickel dimethylglyoximate, Ni(C₄H₇N₂O₂)₂, which is dried at 110–120 °C and weighed. Ni = 0.2031 × mass of precipitate.

Key points

• Dissolve about 0.5 g sample in HCl + HNO₃ (Fe → Fe³⁺); boil off oxides of nitrogen; dilute.
• Add tartaric acid (or citric acid): it complexes Fe³⁺ (also Cr³⁺, Al³⁺), so they do not precipitate as hydroxides.
• Warm to 60–80 °C, add 1 % alcoholic dimethylglyoxime, then ammonia until just ammoniacal (pH about 8): red precipitate.
• Digest, filter on a weighed G4 crucible, wash, dry at 110–120 °C, weigh; % Ni = mass of precipitate × 0.2031 × 100 / mass of sample.
• Care: avoid a large excess of reagent; Pd interferes; Co needs more reagent.