No abstract

Upon addition of Cr VI to a solution of ethylenediaminetetraacetic acid (EDTA) and Mn II , a transient species appears which has an absorption maximum at 500 nm. Kinetic studies of the outer-sphere oxidation of the Mn II -EDTA complex with the Cr 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 OS ¼ 1:75 Â 10 2 and 1.66 Â 10 3 mol À2 dm 6 for [EDTA] and [Mn II ] variations, respectively). The effect of total [EDTA], [Mn II ], [Cr VI ] and [HClO 4] on the rate of the reaction was determined. On addition of HClO 4 , there is a decrease in the rate constants. The reaction product is the Cr III -EDTA complex with k max ¼ 400 and 550 nm. On the basis of the various observations and product characterization a most plausible outer-sphere mechanism has been envisaged.