Thermodynamic properties of aqueous mixed ternaries { y NH 4Cl+(1− y) BaCl 2 } (aq) and { y NH 4Cl+(1− y) CaCl 2 } (aq) at 298.15 K

Abstract

Hygrometric measurements of the water activity are reported for the thermodynamic properties of the mixed aqueous electrolyte systems of ammonium–calcium chloride and ammonium–barium chloride at 298.15 K. The measurements were made at a large number of total molalities, varying from 0.4 mol kg −1 to saturation at three ionic-strength fractions ( y ) of NH 4Cl for the systems NH 4Cl–CaCl 2 (aq) and NH 4Cl–BaCl 2 (aq) with y = 0.20 , 0.50 and 0.80. The experimental data are reported as water activities and osmotic coefficients at various molalities, along with derived values of the activity coefficients of both solutes. The ranges of water activities a w are 0.800–0.989 for ammonium–barium chlorides and a w = 0.560 – 0.989 for ammonium–calcium chlorides. The activity coefficients were calculated by means of a thermodynamic model based on a variant of the Pitzer ion-interaction equations with extended binary parameters. However, the results were also compared for the precision of the presentation of the osmotic coefficients using an extended model with the calculations of the Zdanovskii–Stokes–Robinson, Kusik and Meissner, Robinson and Stokes, Lietzke and Stoughton, Reilly, Wood and Robinson, and Pitzer models.