Estimation of Activities in the Aqueous Solution Systems of HCl–NaCl and HCl–NiCl<SUB>2</SUB> Using the Pitzer Method

Abstract

Parameterizations based on the literature activity data have been carried out for the activities of water and the solutes in the aqueous solution systems of HCl–NaCl and HCl–NiCl2 at 298 K in terms of the Pitzer theory without explicitly considering complex formation. The single electrolyte parameters for HCl, NaCl, and NiCl2 were determined from the osmotic coefficients for the corresponding single electrolyte solutions. Extra parameters of β were included in the single electrolyte parameters for HCl and NiCl2 to extend the applicable concentration ranges. Three kinds of activity data for the aqueous solution of HCl–NaCl, namely, the mean activity coefficients of HCl calculated by the Harned rule, those of NaCl calculated from the solubilities of NaCl, and the osmotic coefficients measured by the transpiration method, were simultaneously submitted to the weighted linear least-squares analysis to determine the mixed electrolyte parameters. Similarly, two kinds of activity data for the aqueous solution of HCl–NiCl2, namely, the mean activity coefficients of HCl by the emf measurement and the osmotic coefficients by the transpiration method, were simultaneously employed. The χ2-tests of significance indicated that the Pitzer parameters obtained in this study can reproduce these activity data with no statistically significant error for both mixed solution systems. As a result, the mean activity coefficients of the solutes in these solution systems calculated by the parameters obtained in this study are in good agreement with those calculated by the McKay-Perring method.