Thermodynamics of concentrated electrolyte mixtures. I. Activity coefficients in aqueous NaCl−CaCl2 at 25°C

Abstract

The activity coefficients of NaCl and CaCl2 in NaCl−CaCl2 aqueous mixtures have been measured at 25°C in the ionic strength range I=0.1–20. Where NaCl solubility permitted, both activity coefficients were measured over the whole range of compositions from pure NaCl to pure CaCl2 at constant I. The measurements were made using Na and Ca ion-selective electrodes vs. a Cl ion-selective electrode. The data are fitted to Harned equations of the form $$log \gamma _A = log \gamma _A^0 - \alpha _{AB} y_B - \beta _{AB} y_B^2$$ and were also analyzed using the Pitzer formalism. Excess free energies of mixing are calculated and presented in the I=0.1–5.0 range and the Friedman parameters calculated.