The behaviour of electrolytes in mixed solvents. Part II.—The effect of lithium chloride on the activities of water and alcohol in mixed solutions

Abstract

In the interaction between ions and solvent molecules, two types of physical effects have been recognised. The first, solvation, may be ascribed, in the absence of definite chemical compound formation between the ions and the solvent, to the attraction exerted by the electric field of the ions on the polarisable molecules of the solvent. Since the elements of a polarisable medium tend to move into those regions where the electric field is greatest, the molecules of water in aqueous salt solutions will tend to congregate round the ions and will be held by quite considerable forces. In the presence of second substance, having a lower dielectric constant than water, this gives rise to the second or salting-out effect. Since water molecules are attracted by the ions more strongly than those of the other substance, the latter may be displaced or salted-out from the vicinity of the ions and their activity in the solution consequently increased. This effect has been extensively studied in dilute aqueous solutions either by means of solubility measurements with sparingly soluble non-electrolytes or by experiments on the distribution of the non-electrolyte between the aqueous solution and an immiscible solvent in which the electrolyte is not soluble.