THERMODYNAMICS OF ELECTROLYTES IN MIXED-SOLVENTS - APPLICATION OF PITZERS THERMODYNAMIC EQUATIONS TO ACTIVITY-COEFFICIENTS OF 1-1 ELECTROLYTES IN METHANOL-WATER MIXTURES

Thermodynamic properties of 1:1 electrolytes in mixed solvent systems have been investigated by using Pitzer's thermodynamic treatment of electrolyte solutions in aqueous medium. It has been shown that these equations are formally applicable to mixed solvents systems also. Using the same values for the b and α parameters in the mixed solvents as in aqueous systems, we have evaluated the two parameters, βMX(0) and βMX(1), governing the second virial coefficient βMXγ for HCl, LiCl, NaCl, and KCl in methanol-water mixtures. Very high negative values for βMX(1) and large positive values for βMX(0) have been obtained for alkali halides in these media. This behavior of βMX(1) and βMX(0) has been attributed to the role of the electrostatic interaction term in the second virial coefficients for electrolytes in these media. It has been shown that 2:2 electrolytes in an aqueous medium behave in a similar way. The variations of βMX(0) and βMX(1) with 1/D further suggest the presence of strong attractive forces in methanol-rich media, indicating ion association. Large negative values of βMX(1) and ion association have been shown to be related. © 1979 American Chemical Society.