Preferential solvation of ions in mixed solvents. Part 2.—The solvent composition near the ion

Abstract

The quasi-lattice quasi-chemical theory of preferential solvation that was related previously to the Gibbs free energy of transfer of an ion from a reference solvent to a mixture of solvents has now been extended to yield the actual amount of the preferential solvation of the ion. This is defined as δ_X1=x^L₁–x₁, the excess (or deficiency) of the local mole fraction of the solvent S₁ in the vicinity of the ion X over its mole fraction in the bulk, in a very dilute solution of X, in the mixture of solvents S₁ and S₂. The preferential solvation obtained for six cases as illustrations (sodium, silver and chloride ions in aqueous dimethyl sulphoxide and acetonitrile) is related to the equilibrium constants for solvent exchange.