Isopiestic Determination of the Osmotic and Activity Coefficients of NaCl + SrCl2 + H2O at 298.15 K and Representation with an Extended Ion-Interaction Model

Abstract

Isopiestic vapor-pressure measurements were made at 298.15 K for aqueous NaCl + SrCl2 solutions using NaCl(aq) as the reference standard. The measurements for these ternary solutions were made at NaCl ionic strength fractions of y1 = 0.17066, 0.47366, and 0.82682 for the water activity range of 0.9835 = aw = 0.8710. Our results, and those from two previous isopiestic studies, were combined and used with previously determined parameters for NaCl(aq) and those determined here for SrCl2(aq) to evaluate mixing parameters S? Na,Sr = (0.0562 ± 0.0007) kg·mol-1 and ?Na,Sr,Cl = -(0.00705 ± 0.00017) kg2· mol-2 for an extended form of Pitzer's ion-interaction model. These model parameters are valid for ionic strengths of I = 7.0 mol·kg -1, where higher-order electrostatic effects have been included in the mixture model. If the fitting range is extended to the saturated solution molalities, then S?Na,Sr = (0.07885 ± 0.00195) kg·mol-1, and ?Na,Sr,Cl = -(0.01230 ± 0.00033) kg2·mol-2. The extended ion-interaction model parameters obtained from available isopiestic data for SrCl 2(aq) at 298.15 K yield recommended values of the water activities and osmotic and activity coefficients