Abstract
The electrode reaction Hg(II)/Hg in complex chloride solutions with dimethyl sulfoxide as solvent has been investigated at the equilibrium potential by the faradaic impedance method and a cyclic current-step method. The ionic strength was 1 M with ammonium perchlorate as supporting electrolyte, and the temperature was 25°C. Double-layer data have been determined by electrocapillary measurements. From the results of the kinetic measurements at ligand numbers ≤1.1 or ≥2.3 it is concluded that the overall charge transfer proceeds step-wise. The solvated Hg2+ and Hg22+ as well as the complexes HgClj2−j and the dinuclear Hg2Cl3+ contribute to the exchange current density. The rate constant of the step HgClj2−j/ Hg(I) is found to increase with the number of Cl− coordinated. This increase can be correlated to a decrease in solvation and a lengthening of the Hg−Cl distance. For 1.1 << 2.3, impedance measurements indicate a rate-controlling adsorption step. It is suggested that the uncharged HgCl2 then forms an adsorbed network on the mercury surface.
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