Solubility and solvation in mixed solvent systems

The solubility of solutes in mixed solvents depends primarily on the solvation of the solutes or their constituent ions by the components of the solvent mixtures. Complications may arise if different crystal solvates are formed or if solute-solute interactions are appreciable. In their absence the standard molar Gibbs energies of solution measure the corresponding quantities of solvation, ASOIVG' , or transfer , AtrG'. The preferential solvation of solutes is described by the composition dependence of AtrG' and is analyzed in terms of the quasi-lattice quasi-chemical (QLQC) or the inverse KirkwoodBuff integral (IKBI) methods. These relate AtrG' to the solvation in the two neat solvents, and in turn to certain properties (polarity, hydrogen-bonding ability, size) of the solvents. These considerations are illustrated by several cases, involving salts and non-electrolytes.