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Kinetics and Mechanism of Oxidation of Co (II) Edta by Chromium (VI) : Effect of Micelle

D. Surya Kala, M. K. Chakravarthy, K. Rama Krishna and P. V. Subba Rao

The kinetics of oxidation of metal ion complex [Co (II) EDTA] by chromium (VI) in perchloric acid medium has been investigated spectrophotometrically at 535 nm. The reaction is first order with respect to complex and the oxidant, and markedly inhibited by H+ under the conditions [Cr(VI)] << [Co(II)EDTA]. The reaction obeys the following rate law with respect to EDTA is as follows. K [H ] kK [Co(II)EDTA] [Cr(VI)] [CoYH O ] dt d a 2 a t 2 + − + = where Y = EDTA in the tetra negative form. In the oxidation of Co (II) EDTA by Cr (VI) anionic micelle (sodium dodecyl sulphate) caused acceleration at sub micelle concentration; where as neutral micelle (triton X-100) caused deceleration in rate. A possible mechanism consistent with the observed results is proposed.