Thermodynamics of phase equilibria of aqueous (lithium sulfate + alkali-metal sulfate) (alkali metal: Na, K, and Rb), and (sodium sulfate + rubidium sulfate), at 298.15 K using Pitzer's model

Osmotic coefficients for aqueous (lithium sulfate + alkali-metal sulfate) (alkali metal: Na, K, and Rb), and (sodium sulfate + rubidium sulfate), have been measured isopiestically at 298.15 K. Parameters of Pitzer's model have been calculated from these measurements. The predicted solubility for the above systems using Pitzer's approach shows good agreement with experimental results. Enthalpies of solution of alkali-metal double sulfates formed in the studied systems have been measured. Based on experimental results, standard molar Gibbs energies of formation, enthalpies of formation, and entropies of alkali-metal double sulfates have been calculated.