Experiment 5 Gravimetric Determination of Nickel in a Nichrome Alloy

EXPERIMENT 5 GRAVIMETRIC DETERMINATION OF NICKEL IN A NICHROME ALLOY 

Nickel forms a red chelate with dimethylglyoxime (DMG), which is quite suitable for gravimetric analysis. Precipitation of the chelate is complete in an acetic acid-acetate buffer or in an ammoniacal solution. Acetate buffer is generally used when Zn, Fe, or Mn is present in the alloy. The sample given to you is a nichrome alloy that has Ni (approximately 60%), Cr, and Fe as the major constituents. Interference from Cr and Fe is removed by complexation with tartrate or citrate ions. Precipitation is then carried out in an ammoniacal solution. The Ni content is calculated from the weight of the precipitate (see Table 10.2 for the formula). 

Obtain the alloy sample from your instructor. 

Prepare three sintered-glass filter crucibles. Dry to a constant weight of 0.3 to 0.4 mg. (Repeated heatings, see Experiment 3.) 

Drying and weighing the precipitate. Place the crucibles in beakers labeled with your name and covered with watch glasses). Dry in the oven for 1-2 h at 110 to 130°C. Cool the crucibles in a desiccator (for 30 to 40 min) and weigh accurately. Reheat for 1-h periods necessary to obtain weights constant to within 0.3 to 0.4 mg. 

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