Abstract
The electrochemical behaviour of the Zn 2+/Zn(Hg) couple has been studied in aqueous mixtures of 1,2-propanediol (PD) containing 5.0 × 10 −2 mol dm −3 LiClO 4 as background electrolyte by polarography and cyclic voltammetry. The reversible half-wave potentials, the diffusion coefficients and the Walden products for Zn 2+, as well as the transfer coefficients and the apparent standard rate constants for the Zn 2+/Zn(Hg) system, were determined. The standard Gibbs energies of transfer of 1 mol of Zn 2+ ions from water to PD-water mixtures (Δ G 0 t) were calculated from the reversible half-wave potentials referred to the Fic +/Foc scale and their values were always negative, indicating a higher stability of Zn 2+ in aqueous PD solutions than in pure water due to the preferential solvation of Zn 2+ 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 the changes in the kinetics of the Zn 2+/Zn(Hg) system with PD mole fraction depend mainly on the surface phase composition. The mechanism of the cathodic and anodic processes of this system under irreversible conditions is discussed.
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