Kinetic Approach to the Reduction of Ethylenediaminetetraacetatoferrate(III) Complex by Iodide Ion in Aqueous Acidic Medium

Abstract

The kinetic approach to the reduction of ethylenediaminetetraacetatoferrate(III) complex (hereafter [Fe(III)EDTA]-) by iodide ion has been studied spectrophotometrically in an aqueous acidic medium. The study was carried out under pseudo-first order conditions of an excess of iodide ion concentration at 28 ± 1, ionic strength (I) = 0.43 coulomb2 mol dm-3 (KNO3) and [H+] = 5.0 10-2 mol dm-3. The [Fe(III)EDTA]- complex was reduced according to the reaction;
 2[Fe(III)EDTA]- + 2I- → 2[Fe(II)EDTA]2- + I2
 The rate law is - d[Fe(III)EDTA-]/dt = (a + b[H+])[Fe(III)EDTA-][I-]
 The rate of the reaction is first order in oxidant and reductant concentrations, and displayed positive Brønsted-Debye salt effect. On the basis of catalysis by added cation, Michaelis-Menten plots and the absence of intermediates, the outer-sphere electron transfer mechanism is proposed for the reaction.