Titration of Alkali Cyanide with Nickel Sulfate Solution

Abstract

The titrations of alkali cyanide with standard nickel sulfate solution in the presence of murexide were studied in comparison with the Liebig-Denigès method. To a sample solution containing 0.3g alkali cyanide in a 300ml conical beaker, 8ml 6N ammonium hydroxide is added, diluted to 100ml with water, 0.03-0.05g murexide powder (0.4g ammonium purpurate+100g sodium chloride) added as an indicator, and titrated immediately with a standard 0.1N nickel sulfate until all the cyanide has complexed with the nickel and the color of the solution changed from violet-pink to clear yellow. Although the standardization of 0.1N nickel sulfate could be carried out gravimetrically in the usual dimethylglyoxime method (I), and volumetrically against the standard EDTA solution (II) or against the standard 0.1N silver nitrate solution (III) by comparing the volume of 0.1N nickel sulfate solution required in the titration of the same volume of a potassium cyanide solution by the present method, with that of the standard silver solution by Liebig-Denigès method, the latter method gave better result when a nickel salt, with which the standard solutions were prepared, was contaminated with considerable amounts of cobalt, copper etc. The present method proved excellent reproducibility and showed a sharp end point unless too much murexide powder was added. The results obtained were closely consistent with that of Liebig-Denigès method. An addition of 2-30ml 6N ammonium hydroxide gave the constant result. No difficulty was found in the procedure in the presence of considerable amounts of halide, carbonate, acetate, thiocyanate, nitrate, sulfate, phosphate, oxalate, ferrocyanide and chromate, with the exception of ferricyanide, nickel, cobalt, silver, copper and calcium. The disturbance by the presence of calcium was removed by adding an excess amount of sodium oxalate before the titration. In the end, the present method is recommended especially for the technical routine analysis instead of the usual argentometry on accoun t of a lower cost of nickelsalts and their applicability for turbid sample solutions.