Abstract
The kinetics of the oxidation of EDTA by Cr(VI) in the presence of perchloric acid has been followed by visible spectrophotometry at 350 nm. The effects of the total [Cr(VI)], [EDTA] and [HClO4] on the rate are determined. The reaction is first-order each in [Cr(VI)] and [EDTA] whereas the rate-[H+] profile suggests complicated kinetic features. Addition of Mn(II) has a large accelerating influence. These observations permit to propose detailed mechanism for the oxidation of EDTA by Cr(VI) in the presence and absence of Mn(II). The catalytic effect of Mn(II) has been ascribed to a one-step, three-electron process in which a termolecular complex is formed between the oxidant, Mn(II) and EDTA. The oxidation has the rate expression:
-d[Cr-VI](T)/dt = k(1)K(an)[H+](2) K-1 [Cr-VI](T)[EDTA](T)/(1/[H+] + K-a3 +K-1 + K-1 K-a3 [H+]).