Thermodynamics of Preferential Solvation of Electrolytes in Binary Solvent Mixtures

Abstract

The solvation changes of an ion, as the composition of a binary solvent is varied, can be treated on the basis of n successive equilibria where n is the solvation number. From a detailed consideration of the thermodynamics of preferential solvation, it is possible to define a free energy of preferential solvation ∆G ps ө and relate it to the more familiar free energy of trans fer, ∆G ps ө determinable for a neutral combination of ions from emf measurements. The treatment can be modified to include a case of change of solvation number and to non-statis tical distribution of the solvated species. When separate sol vent NMR signals from solvation shells can be detected or mixed solvates isolated, a further development enables a satis factory explanation to be given for the observed distribution of solvated species.

Preferential Solvation of the Sodium Cation in Binary Mixtures of Tetrahydrofuran with Unidentate Nitrogen Ligands

“…It is more powerful than existing treatments. For instance, the Covington equations [6] are merely a particular case of the Hill-Adair [43] equations under the absence of any positive or negative cooperativity. In order to apply the Covington equations [6], one has to make restrictive assumptions about the equality of the K, values.…”

“…For instance, the Covington equations [6] are merely a particular case of the Hill-Adair [43] equations under the absence of any positive or negative cooperativity. In order to apply the Covington equations [6], one has to make restrictive assumptions about the equality of the K, values. The merit of the Hill representation is to provide a clean and easy graphic access to the intrinsic equilibrium constants, while at the same time testing for the absence of cooperativity in the system.…”

“…The two crucial assumptions made in this study are the additivity of the chemical shifts hi, for which there is ample empirical support [6] [32], and tetracoordination of the sodium cation in these solutions of THF and amines: we shall examine critically the latter assumption in the next article in this series.…”

“…Mathematically, preferential solvation of a tetracoordinated ion, and binding of a ligand to one of four sites in a biomolecule, constitute one and the same problem. The Hill formalism, hitherto neglected in studies of preferential solvation, provides a better understanding of the phenomenon than the existing and sometimes less powerful formalisms [6] [36]. We study here unidentate ligands, which will serve as references for determining the magnitude of the chelate effects present with bidentate and polydentate ligands WI.…”

Solvation effect on kinetic rate constant of reactions in supercritical solvents

“…Indeed, preferential solvation has been theoretically studied and experimentally observed in aqueous organic and electrolyte systems under ambient conditions (Ben-Naim, 1988, 1990Covington and Newman, 1976) for many years. In fact, there are two main aspects to consider, namely: (1) even a small degree of preferential solvation of one species over another (density perturbation) at near-critical conditions (in contrast to normal conditions) will be substantially magnified by compressibility effects (propagation of the perturbation), resulting in large partial molar volumes (see Eq.…”