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Kinetics andmechanismof formation of 1:1 complex between chromium(III) with edta in aqueous acidicmedia

Mohamed A.El-Hag, Gibrel F.Saleh

The kinetics of the formation of 1:1 complex of chromium (III) with ethylenediaminetetraacetate (EDTA) was followed spectrophotometrically at lmax = 552 nm. The reaction was found to be first order in chromium (III). Increasing the edta concentration from 2.2x10-2 to 8.8 mol dm-3 accelerated the reaction rate. Increasing the pH from 3.3 to 4.7 also accelerate the reaction rate, while the reaction rate was retarded by increasing ionic strength and dielectric constant of the reaction medium. A mechanism was suggested to account for the results obtained which involves ion pair formation between the various species of the reactants. Value of 37.1 ± 3 kJ mol-1 was obtained for the energy of activation and -195.6 ± 6 K-1 mol-1 for the entropy of activation indicate an associative mechanism for the reaction. The logarithms of the formation constant of 1:1 complex formed were found to be 7.31.