Adsorption of inorganic anions on a mercury electrode from solutions in formamide II. Adsorption of chloride and nitrate ions

Abstract

Specific adsorption of chloride and nitrate ions on a mercury electrode from solutions of the respective potassium salts in formamide has been studied by measurements of the double layer capacity and the interfacial tension as a function of concentration. Specific adsorption of nitrate although weak is confirmed by comparison of the results with the diffuse layer theory. Chloride is more strongly adsorbed but its behavior, as in aqueous solutions, is more complex than that of the corresponding iodide system. The results are examined in terms of a low-coverage approximation to Frumkin's isotherm at constant charge on the metal, with allowance for the variation of the diffuse layer potential, and also at constant potential across the double layer. The adsorption of chloride obeys neither form of isotherm whereas the adsorption of iodide can be described by both. Adsorbed chloride ions produce an unusually large potential difference across the inner region of the double layer which is consistent with a mean dielectric constant of 3 compared with a value of 7 calculated for the iodide system.