Strong Electrolytes

Abstract

IN the original form of the Debye-Hückel theory, the solvent enters only as the medium, having a certain dielectric constant, through which the electric forces between the ions act. In his extension of the theory to concentrated solutions (Physikal. Zeitschrift, 26, 93; 1925) Hückel discussed at some length the effect of the electric field of the ions on the solvent molecules, and pointed out that polarisable molecules tend to congregate round an ion where the electric field strength is greatest, thereby tending to displace other ions from its vicinity. Hückel considered that the effect of this behaviour was obtained by introducing into the equations “the phenomenological law that the dielectric constant of the solution diminishes with increasing electrolyte concentration.” While his equations were capable of reproducing the activity coefficients of salts, even in concentrated solutions, using constants obtained from the data themselves, it is doubtful whether these constants have the postulated relation with the dielectric constant lowerings actually produced by electrolytes (cf. Harned, J. Amer. Chem. Soc., 48, 326; 1926).