A Priori Prediction of Thermodynamic Properties of Electrolytes in Mixed Aqueous–Organic Solvents to Extreme Temperatures

Abstract

The unified theory of electrolytes (J. Phys. Chem. B 2009, 113, 2398-2404) for predicting the standard state thermodynamic properties of aqueous electrolytes has been extended to include mixed solvent systems. The solubility of solid sodium chloride in mixed solvents (methanol/water concentration up to 75% w/w) was also measured up to 466 K and pressures near 7 MPa. The present model, together with a simple modification of Pitzer's thermodynamic treatment of aqueous solutions, allows a priori prediction of solubility of electrolytes in aqueous/organic systems to extreme temperatures and pressures. Solubility is predicted for sodium chloride and potassium chloride in mixed solvents (methanol/water, ethanol/water) over a wide range of temperatures and compositions from the extension of the unified theory of electrolytes to mixed solvents. Comparisons indicate good agreement in all cases to well within the uncertainties of the experimental data. The stoichiometric activity coefficients of saturated solution of sodium chloride in methanol/water mixed solvents were calculated up to 473.15 K. The stoichiometric activity coefficients, as a function of temperature at all concentrations (0 ≤ m ≤ m(sat)) and the entire range of mole fraction of methanol, were also calculated up to 473.15 K. The novelty of the present approach is that no additional parameters are required to account for the medium effect.