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Corresponding Author

MANSOUR, MOHAMED

Document Type

Original Article

Subject Areas

Chemistry

Keywords

Kinetics; Oxidation; L-ascorbic acid; Chromium (VI)

Abstract

The kinetics of oxidation of L-ascorbic acid by potassium chromate was studied as a function of pH, L-ascorbic acid concentration and temperature using the spectrophotometric technique. The rate of reaction is first order with respect to the concentration of each reactant and increases as [H+] increases. The kinetic data indicate involvement of the monoprotonated ascorbate species (HA-) in the redox process. A mechanism involving the formation of chromium (VI)- ascorbate intermediate is a rate-determining step followed by a redox step was suggested. The activation enthalpy and activation entropy changes for the reaction have been calculated to be ΔH*= 69 kJmol-1 and ΔS*= -209 JK-1 mol-1, respectively.

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