Modeling aqueous electrolyte solutions. Part 2. Weak electrolytes

In this work the ePC-SAFT model is applied to weak electrolytes, such as weak acids or salts that do form ion pairs. Considering an association/dissociation equilibrium accounts for the fact that the electrolytes are not fully dissociated. Applying this approach, modeling the mean ionic activity coefficients (MIAC) as well as the water activity coefficients (WAC) is in very good agreement with experimental data for the aqueous HF system as well as for solutions of cadmium halides or alkali acetates. Experimental MIACs of ZnBr2 and ZnI2 reveal the formation of more than one complex in aqueous solutions. Implementing a simultaneous two-step ion-pairing mechanism also allows the modeling of the MIAC of these zinc salts in water.