The behaviour of electrolytes in mixed solvents VI—The electrical conductivities of some salts in water-ethyl alcohol solutions

Abstract

Extensive measurements of the conductivities of salts in mixed solvents have been made by Jones and his co-workers.* Although they were neither sufficiently accurate, nor carried to a sufficiently low concentra­tion to define the limiting conductivities at infinite dilution, these measure­ments give a good idea of the general nature of the phenomena which are to be observed in mixed solvents. For salts which are strong electro­lytes in both pure solvents, a close parallelism was generally found between the conductivities and the fluidity of the solvents, but with others, particularly salts of cobalt, nickel, copper, etc., which frequently have very small conductivities in non-aqueous media, the matter appears to be complicated by changes in the degree of dissociation. Apart from this, a considerable amount of work has been done on acids in water- alcoholic solvents,! and on the effect of the addition of small quantities of water to dilute solutions of electrolytes in various solvents. It is found that in hydroxylic and similar solvents the conductivity of strong acids is decreased by the addition of water to a much greater extent than can be accounted for by the change of viscosity, but with other strong uni-univalent salts the effect is of the same order as the viscosity change. This, no doubt, arises from the different mechanism of migration, and can be explained qualitatively at least in terms of recent theories of the mobility of the hydrogen ion.§ On the other hand, if the solute is a weak electrolyte in the non-aqueous solvent the addition of water may cause a large increase of conductivity by increasing the degree of dis­ sociation.* Although numerous measurements have been made of the effect of small additions of water to non-aqueous solutions, and a few of the addition of non-electrolytes to aqueous solutions of salts, in no case have measurements been made over the whole range of mixed solvents with sufficient accuracy to determine the conductivities at infinite dilution. We have therefore determined the conductivities at small concentrations in a series of mixtures of water and ethyl alcohol of lithium chloride and potassium iodide, two salts which are strong electrolytes in both of the pure solvents and have derived the equivalent conductivities at infinite dilution. We have also examined the behaviour in these solvents of zinc chloride, a salt which is a strong electrolyte in water and a very weak electrolyte in ethyl alcohol.