THERMODYNAMIC PROPERTIES OF NONELECTROLYTE SOLUTIONS .4. ESTIMATION AND MATHEMATICAL REPRESENTATION OF SOLUTE ACTIVITY-COEFFICIENTS AND SOLUBILITIES IN BINARY SOLVENTS USING THE NIBS AND MODIFIED WILSON EQUATIONS

The limitations and applications of the various nearly ideal binary solvent (NIBS) and Modified Wilson models for predicting the thermochemical properties of solutes dissolved in binary solvent mixtures are examined using published solute solubility and infinite dilution activity coefficient data for 72 systems. Expressions derived from the basic NIBS and extended NIBS models provide very reasonable predictions for anthracene, thianthrene and carbazole solubilities in systems containing both specific and non-specific interactions. For many of the systems considered, deviations between experimental and NIBS predictions are of the order of 6% or less. In comparison, the Modified Wilson equation grossly underpredicts the observed solubilities, with deviations for several of the carbazole systems being 40% or more. Both models can serve as a point-of-departure for the mathematical representation of experimental solubility data, and two possible descriptive forms are suggested.