Return to aqueous electrolyte page

Aqueous Solutions of electrolytes and non-electrolytes

Solutions containing electrolytes and more than one solvent are often called "mixed solvent systems". Mixed solvent systems containing one salt have been considered pseudo binary solutions consisting of "mixed solvent" and salt. This view makes it difficult to model "mixed solvent systems" because the standard chemical potentials of ions are functions of the solvent composition. It is necessary to know the numerical values of the standard chemical potentials of ions at the current solvent composition in order to perform solid-liquid equilibrium and liquid-liquid equilibrium calculations in such systems.

By considering water to be the only solvent and electrolytes and non-electrolytes to be solutes, the thermodynamic modeling of such systems become more straightforward. And more importantly, this view actually makes it possible to calculate solid-liquid-equilibria, vapor-liquid equilibria, and liquid-liquid equilibria with great accuracy using the same set of parameters in the relatively simple thermodynamic model, the Extended UNIQUAC model.

In the Extended UNIQUAC model, the relative permittivity (electric constant) is considered independent of the mixture composition. The relative permittivity is used for calculating the electrostatic contribution to the deviation from ideality.