MEDIUM EFFECT ON THE ELECTROCHEMICAL-BEHAVIOR OF THE ZN2+ ZN(HG) SYSTEM IN AQUEOUS 1,2-PROPANEDIOL SOLUTIONS/

The electrochemical behaviour of the Zn2+/Zn(Hg) couple has been studi ed in aqueous mixtures of 1,2-propanediol (PD) containing 5.0 x 10(-2) mol dm-3 LiClO4 as background electrolyte by polarography and cyclic voltammetry. The reversible half-wave potentials, the diffusion coeffi cients and the Walden products for Zn2+, as well as the transfer coeff icients and the apparent standard rate constants for the Zn2+/Zn(Hg) s ystem, were determined. The standard Gibbs energies of transfer of 1 m ol of Zn2+ ions from water to PD-water mixtures (DELTAG(t)0) were calc ulated from the reversible half-wave potentials referred to the Fic+/F oc scale and their values were always negative, indicating a higher st ability of Zn2+ in aqueous PD solutions than in pure water due to the preferential solvation of Zn2+ by PD. The analysis of the variation of the Walden product with solvent composition indicates an enhancement of the solvent structure in the water-rich region. It was found that t he changes in the kinetics of the Zn2+/Zn(Hg) system with PD mole frac tion depend mainly on the surface phase composition. The mechanism of the cathodic and anodic processes of this system under irreversible co nditions is discussed.