Thermodynamics of electrolytes in aqueous systems containing both ionic and nonionic solutes. Application of the Pitzer–Simonson–Clegg equations to activity coefficients and solubilities of 1:1 electrolytes in four electrolyte–non-electrolyte–H2O ternary systems at 298.15 K

Abstract

The Pitzer–Simonson–Clegg equation is applied to the salt activity coefficients and solubilities in ternary systems NaCl–sucrose–H₂O, NaCl–urea–H₂O, NaCl–mannitol–H₂O, and KCl–glycine–H₂O at 298.15 K. The results are compared with the isopiestic, emf, and solubility measurements. The model with a zero parameter (Y_l,n,MX) relating interactions between two neutral species and two ions is valid at high electrolyte:non-electrolyte ratios. The introduction of the macroscopic relative permittivity, the mean molar mass, and the density of non-electrolyte–H₂O mixture in the Debye–Hückel constant and the "‘closest approach’' parameter significantly worsens the model calculations. The model predictions are also slightly worsened if a constant nonzero Y_l,n,MX is added. The accuracy of the model at lower salt proportions can be considerably improved by making the parameter Y_l,n,MX dependent either on ionic strength or on ionic strength and mole fraction of nonionic solute. Under these conditions, the model can provide good description of salt activity coefficients and solubilities over entire experimental composition ranges. These results suggest that a composition dependent parameter Y_l,n,MX is needed for the present four systems.