Inclusion of Ionic Hydration and Association in the MSA-NRTL Model for a Description of the Thermodynamic Properties of Aqueous Ionic Solutions: Application to Solutions of Associating Acids

Ionic hydration and association are included in the MSA-NRTL model for a description of the thermodynamic properties of aqueous ionic solutions. Hydration effects are introduced using the classic model of Robinson and Stokes, in which hydration numbers are independent of salt concentration. Association is accounted for through a mass action law. New compact conversion formulas are given expressing the individual ionic, and mean salt, activity coefficients at the Lewis-Randall level. The model is applied to the representation of strong and associating aqueous electrolytes at 25 °C. In the case of solutions of associating acids, its ability to also describe the speciation of the acid is examined.