HIGH-TEMPERATURE THERMODYNAMICS OF AQUEOUS ALKALI-METAL SALTS

Heat capacities and densities of aqueous solutions of four alkali-metal halides (NaF, KF, KCl, and KI) and two alkali-metal sulfates (Na2SO4 and K2SO4) have been measured at temperatures from 298.15 K to 373.15 K and at the pressure 0.6 MPa over the molality ranges 0.03 mol·kg-1 to 0.44 mol·kg-1, 0.10 mol·kg-1 to 2.10 mol·kg-1, 0·03 mol·kg-1 to 2.01 mol·kg-1, 0.04 mol·kg-1 to 0.60 mol·kg-1, 0.05 mol·kg-1 to 1.53 mol·kg-1, and 0.03 mol·kg-1 to 0.40 mol·kg-1, respectively. The measurements were done using a flow differential-heat-capacity calorimeter in series with a vibrating-tube densimeter. Pitzer's ion-interaction model was used to analyse these results and literature values of comparable precision. Equations for the apparent molar heat capacities and volumes are reported, and consistent sets of ionic partial molar heat capacities and volumes at 298.15 K and 373.15 K, relative to the conventions: C∞p, 2(H+,qa) = 0 and V∞2(H+,aq) = 0, were calculated. Activity coefficients were also calculated for NaF and KF for the temperature range from 298.15 K to 473 K. © 1992 Academic Press Limited All rights reserved.