Electromotive Force Studies of Cadmium Chloride in Water, Water‐Methanol, and Methanol Solutions

Abstract

The emf of cadmium chloride was determined in water, water‐methanol, and methanol solvents over a concentration range of 0.0050 to about 0.1000M. Measurements were made using a L&N Type K‐3 potentiometer and an amalgam cell without transference. In order to determine the standard potential of cadmium chloride in the various solvents it was necessary to extrapolate the molality to zero by a suitable linear function of the observed emf. Satisfactory values of the standard potential were determined over the entire solvent, temperature, and concentration ranges by assuming only one method of ionization and simultaneously varying the equilibrium constant as the solvent composition was varied. The justification for decreasing the dissociation constant as the dielectric constant was decreased was based on Bjerrum's theory of ionic association in media other than water. The laborious calculations involved in the determination of the standard potentials were accomplished by using an I.B.M. 7040 computer. The standard potentials which were determined were used to calculate the mean ionic activity coefficients of cadmium chloride in the various solvents. The calculations were made by using the form of the Nernst equation which is applicable to a 2‐1 electrolyte. The activity coefficients of cadmium chloride in the various solvent systems are similar to those determined by other investigators for electrolytes in mixed and nonaqueous solvents. The general behavior is that deviations from the Debye‐Hückel theory occur at lower concentrations as the dielectric constant of the solvent is decreased.