Densities of NaCl(aq) to the temperature 523 K at pressures to 40 MPa measured with a new vibrating-tube densitometer

Abstract

Relative densities of NaCl(aq) with molalities m: 0.165 ≤ m /(mol· kg-1) ≤ 5.484 have been measured with a vibrating-tube densitometer between the temperatures 298 K and 523 K at pressures of 7 MPa and 40 MPa. These results span the pressure and temperature ranges of several earlier volumetric studies of NaCl(aq) and extend to higher molalities than have been reported previously. The densities are in good agreement with published values through T - 523 K. Apparent molar volumes Vφ calculated from the measured density differences have been fitted with the Pitzer ion-interaction treatment, with appropriate expressions chosen for the temperature and pressure dependence of the molality-independent parameters of the model. It was found that the partial molar volume at infinite dilution V∞φ and second- and third-virial parameters β(o)V and Cv were sufficient to represent Vφ at nearly the estimated experimental uncertainly.