Abstract
Upon addition of Cr^sup VI^ to a solution of ethylenediaminetetraacetic acid (EDTA) and Mn^sup II^, a transient species appears which has an absorption maximum at 500 nm. Kinetic studies of the outer-sphere oxidation of the Mn^sup II^-EDTA complex with the Cr^sup VI^-EDTA complex have been investigated by visible spectrophotometry at 25 °C. The formation of a transient species has been characterized spectrophotometrically and the encounter complex formation constants have been determined (K^sub OS^ = 1.75 × 10^sup 2^ and 1.66 × 10^sup 3^ mol^sup -2^ dm^sup 6^ for [EDTA] and [Mn^sup II^] variations, respectively). The effect of total [EDTA], [Mn^sup II^], [Cr^sup VI^] and [HClO^sub 4^] on the rate of the reaction was determined. On addition of HClO^sub 4^, there is a decrease in the rate constants. The reaction product is the Cr^sup III^-EDTA complex with λ^sub max^ = 400 and 550 nm. On the basis of the various observations and product characterization a most plausible outer-sphere mechanism has been envisaged.[PUBLICATION ABSTRACT]