Investigation of electrometric methods for the estimation of copper

Abstract

The previous work on this subject, is considered, showing that no satisfactory methods have so far been produced. The application of monometallic electrode systems to precipitation and oxidation and reduction reactions and the method of conducting titrations are discussed. Bimetallic electrode systems are considered with special reference to a new method due to Foulk and Bawden. The following methods have been Investigated: (1) The precipitation of cuprous thiocyanate from a copper sulphate solution reduced by bisulphite (Muller and Rudolph's method) was found to be too easily influenced by the bisulphite concentration, time of titration and temperature to be practicable. (2) The precipitation of cuprous thiocyanate by excess standard potassium thiocyanate solution and back-titration with silver nitrate was found to give excellent results with copper sulphate concentrations greater than N/25 and in the presence of zinc and iron. (3) The reduction of copper sulphate in hydrochloric acid solution by stannous chloride gives a sharp end-point if the acid concentration is high but the results vary with this concentration and are always too high. (4) The titration of copper sulphate with sodium thiosulphate, potassium cyanide and iodide respectively. These methods are not satisfactory, no distinct end point being obtained. (5) The titration of the iodine liberated by the action of copper sulphate and potassium iodide with thiosulphate gives satisfactory end-points in acetic acid solution using a mono-metallic system of electrodes. Foulk and Bawden's method however gives far sharper end-points and is applicable to copper concentrations greater than N/250 and in the presence of many metals. Adaptations in the presence of ferric salts are discussed. Replacing thiosulphate with arsenlte solution is satisfactory with copper sulphate solutions more concentrated than N/50. Methods 3L and 5 are recommended as satisfactory.