Double-layer studies in ethanolic solutions. Part 2.—Adsorption of iodide ion on mercury from solutions of constant ionic strength

Abstract

The adsorption of iodide ion from ethanolic solutions has been studied at constant ionic strength (0.2 mol dm^–3) at a mercury electrode by measuring the interfacial capacity. The data were analysed to obtain the adsorbed charge density as a function of electrode charge density and bulk iodide concentration. These data are shown to obey a virial isotherm. The isotherm parameters obtained for the ethanol system are compared with results reported earlier in eight other solvents. The standard Gibbs energy of adsorption is shown to be a linear function of the Gibbs energy of iodide ion solvation and the entropy of solvent vaporization, the latter quantity being used as a measure of solvent structure. The dielectric properties of the interface in the presence of iodide adsorption are also examined within the context of a non-primitive model based on the mean spherical approximation. Application of this model at the interface is compared with the corresponding model for solvation in the bulk of the solution in the same solvents.