Abstract
The quasi-lattice
quasi-chemical theory is used with a single fitting parameter (Z, the number of
nearest neighbours) and data independent of the
transfer to solvent mixtures, to describe quantitatively the standard molar
Gibbs free energy of transfer of ions from a reference solvent to solvent
mixtures, ΔGt� (X, W → S1
+ S2), as a function of the composition (mole fraction, x). The
independent data include the ΔGt� to
the two pure solvents and the excess Gibbs free energy of mixing of these
solvents. A defined preferential solvation parameter,
g(x), is a convenient measure that is
obtained from this treatment. The advantages of employing volume fractions, �,
and g(�) rather than mole fractions, x, and g(x), are examined. The theory is
applied to the transfer from water of Cl- to ethanol, of Ag+ to acetonitrile or dimethyl sulfoxide, and of NaCl to methanol, and of Na+ from acetonitrile
to dimethyl sulfoxide as illustrative examples, comparing the calculated values
to experimental data.