Specific adsorption of fluoride ions on mercury and the structure of the mercury/solutions interface

Abstract

The specific adsorption of fluoride ion on mercury has been studied at two temperatures. The unusual adsorption isotherm of the fluoride ion has been analyzed in terms of the equilibrium conditions prevailing across the double layer; a Freundlich-type isotherm describes the surface pressure of the adsorbed ionic film. The inner layer capacitance has been analyzed and its various components calculated, and from the variations of the inner layer capacitance at constant amount of adsorbed charge, the inner layer capacitance in the absence of adsorption has been evaluated. The anodic hump in the capacitance of fluoride solutions is due mainly to the adsorption of F^– ions, and not to adsorbed solvent reorientation. The adsorption of SiF^2–₆ does not lead to a large increase in the double-layer capacitance at anodic potentials.