Thermodynamics Research Center / ThermoML | Journal of Chemical and Engineering Data

ABSTRACT

The binary and ternary aqueous solutions of sodium phosphate or/and sulfate were studied using the hygrometric method from dilution to saturation in the temperature range from (298.15 to 353.15) K. The hygrometric measurements of the binary systems were combined with reference pure water, Na3PO4(s), and Na2SO4(s) solubility data to construct a chemical model that calculates solute and solvent activities from dilute to saturated solution concentration (for (Na3PO4(s)) up to mmax = 9.00 mol*kg 1 at 353.15 K; and up to mmax(Na2SO4(s)) = 3.40 mol*kg 1at 313.15 K). The constructed model was also used to calculate thermodynamic solubility product (Kdeg sp) of Na3PO4(s) and Na2SO4(s) in the temperature range (298.15 to 353.15) K. The excess Gibbs energies of Na3PO4(aq) and Na2SO4(aq) were evaluated at various temperatures. The results for these aqueous solutions were influenced by the effect of hydration shell, with ion association or formation ion pairing. The anion solute PO4 or SO4 influences the hydration in an aqueous solution; indeed the hydrogen bonding of water in the hydration shells of PO43 anion is preeminent over that of SO42 . The mixed electrolyte solutions {(yNa3PO4 + (1 y)Na2SO4}(aq) were also investigated in the temperature range from (298.15 to 353.15) K and at total molalities from dilution (0.10 mol*kg 1) to saturation for different ionic-strength fractions (y) of Na3PO4 with y = 0.20, 0.50, and 0.80. The water activity of mixed salts solutions and related properties such as osmotic and activity coefficients were carried out at various temperatures. The osmotic coefficients data were used to evaluate the mixing parameters of the ion interaction model ?MN and ?MNX in the ternary system Na3PO4 + Na2SO4 + H2O.