Kinetics of the chromic acid oxidation of arsenic(III)

Abstract

The kinetics of oxidation of arsenic(III) by chromium(VI) has been studied in the temperature range 30–45 °C. The energy and entropy of activation, where a high concentration of arsenic(III) reacts with a low concentration of chromium(VI) to give a 1 : 1 complex, have been evaluated to be 9·1 ± 0·6 kcal mol^–1 and –43·5 ± 0·1 cal K^–1 mol^–1 respectively. Corresponding values for reaction of low arsenic(III) with high chromium(VI) concentrations are not widely different from those above and have been found to be 9·4 ± 0·1 kcal mol^–1 and –39·95 ± 0·15 cal K^–1 mol^–1. The formation of an unstable 1 : 1 complex in the latter case is also suggested.