Thermodynamic Properties of Ions in Mixed Solvents

The standard molar enthalpies of dissolution of electrolytes in aqueous cosolvent mixtures are monotonic with the composition only if the cosolvent does not involve a sizable alkyl moiety in its molecules. This is the case for formamide, DMF, urea (treated as if it were a solvent), and DMSO. On the other hand, cosolvents that have a hydrophobic group and enhance the structure of the water in the water-rich region according to Marcus [16,17] show amaximum in the curve in this region 

A useful measure for the interactions in the system is the pair interaction enthalpy /igj, defined as  

Although water (W) is specified here as the reference solvent, it might be any other one, and E and denote the electrolyte (or ion, if ionic values have been derived) and the molality of the cosolvent S. Extensive data are available for E=NaCl and Nal, reproduced in Table 6.3 from the work of Piekarski and Tkaczyk [22], but data are available for a few other salts too. Data of for E=Nal are available for fewer cosolvent when the reference solvents are MeOH, MeCN, and DMF [22]. When 

TABLE 6.3 Pair interaction Enthalpic Parameters, and Heat 

Capacity Parameters c, g gj/J-mol kg-mol for Electrolytes in Mixtures of a Reference Solvent R (W or as Specified) with Cosolvents at 25°C 

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