Apparent molar volumes of aqueous calcium chloride to 250�C, 400 bars, and from molalities of 0.242 to 6.150

Abstract

Relative densities of CaCl 2 (aq) with 0.22≤ml(mol-kg−1)≤6.150 were measured with vibrating- tube densimeters between 25 and 250°C and near 70 and 400 bars. Apparent molar volumes VΦ calculated from the measured density differences were represented with the Pitzer ioninteraction treatment, with appropriate expressions chosen for the temperature and pressure dependence of the virial coefficients of the model. It was found that the partial molar volume at infinite dilution V Φ o , and the second and third virial coefficients B V and C V , were necessary to represent VΦ near the estimated experimental uncertainty. The ionic-strength dependent β(1)v term in the B V coefficient was included in the fit. The representation for VΦ has been integrated with respect to pressure to establish the pressure dependence of excess free energies over the temperature range studied. The volumetric data indicate that the logarithm of the mean ionic activity coefficient, ln γ±(CaCl 2 ), increases by a maximum of 0.3 at 400 bars, 250°C, and 6 mol-kg−1 as compared with its value at saturation pressure.