Activity coefficients for the system HCl + CaCl2+ H2O at various temperatures. Applications of pitzer's equations

Abstract

Activity coefficients of hydrochloric acid in mixed solutions with calcium chloride have been measured at total ionic strengths of 0.1, 0.25, 0.5, 1.0, 1.5 and 2.0 mol kg–1 at nine different temperatures from 278.15 to 318.15 K at intervals of 5 K, and at total ionic strengths of 2.5, 3.0, 3.5, 4.0, 4.5 and 5.0 mol kg–1 from 278.15 to 318.15 K at intervals of 10 K, using e.m.f. cells of the type Pt, H2(g, 1 atm)|HCl(mA), CaCl2(mB)|AgCl|Ag. The results have been interpreted in terms of Pitzer's equations, from which the calculations of the activity coefficients of calcium chloride in the mixtures have been made. The values of SθMN and ψMNX(including higher-order electrostatic effects) and θMN and ψMNX(excluding higher-order effects) were determined based on Pitzer's treatment. The trace activity coefficients of HCl, γtrA(when yB, the ionic strength fraction of CaCl2 in the mixture, equals 1), are also reported. Within the experimental error, Harned's rule is obeyed for hydrochloric acid at all experimental temperatures and over the entire range of ionic strengths studied. In the case of calcium chloride, Harned's rule is a good description only for I= 0.1, 0.25 and 0.5 mol kg–1, over the range of temperatures examined.