Specific adsorption of chloride ions at the mercury/aqueous solution interface

Abstract

The adsorption of chloride ions on mercury from aqueous solutions of KCl + KF at constant ionic strength has been investigated by measurements of the double-layer capacity as a function of concentration. The adsorption can be represented by a one-constant virial form of isotherm with a non-linear charge dependence of the standard free energy of adsorption in contrast to the adsorption of the same ion from KCl solutions. The hump on the anodic branch of the capacity-potential curve arises partially from the effect of a decrease in the capacity at constant amount adsorbed superimposed on an increasing adsorption capacity, and partially from an inflexion in the charge dependence of the amount adsorbed; this in turn arises from the non-linear charge dependence of the standard free energy of adsorption. The constant charge isotherms for Cl^– ion adsorption from KCl and from KCl + KF solutions cannot be superimposed irrespective of the choice of salt activity or mean ionic activity as the concentration variable.