A Study of the Kinetics of the Oxidation of Arsenic (III) by Electrogenerated Iodine in Alkaline Media

The oxidation of As(III) by electrogenerated I₃⁻ was studied in aqueous media for 8.17 ≤ pH ≤ 9.17 using the rotating ring-disk electrode. On the basis of chemical kinetic evidence reported in the literature, it is shown that the mechanism commonly given to account for the observed rate law at low pH is not correct for pH >7. The rate of oxidation of all forms of As(III) is given by -d[As(III)]/dt = k[I₃⁻][H₂AsO₃⁻] + k'[I₂][H_2- AsO₃⁻] where k = (5.65 ± 0.05) X 106 1. mol⁻¹ sec⁻¹ and k′ = (1.75 ± 0.15) X 108 1. mol⁻¹ sec⁻¹.