Polarographic and Coulometric Studies of cis-Dioxalatodiaquochromate(III)

Abstract

Abstract The current-voltage curves of cis-dioxalatodiaquochromate (III) have been recorded at the dropping mercury electrode in various supporting electrolyte solutions. A well-defined wave with a half-wave potential of −1.522 V. vs. SCE was obtained in 0.3 m potassium chloride solutions containing 0.005% gelatin. The limiting current in this case was proved to be diffusion-controlled from its dependence on the effective pressure of mercury on the dropping mercury electrode and from the characteristics of the current-time curve during the life of a mercury drop. The electrode reaction of the complex was found to be irreversible by a study of both the characteristics of the Kalousek polarogram and the relation of log{\bari⁄\barid–\bari)} against E. The number of electrons involved in the reduction was determined by the controlled-potential coulometric method. The coulometric investigation showed that cis-dioxaloto-diaquochromate(III) is reduced to the metal at the dropping mercury electrode. This conclusion was also supported by the detection of chromium from the surface of the mercury pool electrode used in the controlled potential electrolysis. The value of the diffusion coefficien t of cis-dioxalatodiaquochromate (III), calculated for a three-electron reduction, was also reasonable in comparison with those of other chromium (III) complexes.