Solubility and Thermodynamic Properties of Dipotassium or Disodium Hydrogenphosphates in Aqueous Solutions at Various Temperatures

In this investigation, calculated and experimental solubilities of the binary aqueous solutions of dipotassium hydrogenphosphate and disodium hydrogenphosphate have been determined at various temperatures. The experimental solubilities of aqueous solutions were performed for K 2 HPO 4 and Na 2 HPO 4 from m s(exp) = 9.66 to 15.63 mol·kg −1 and m s(exp) = 0.83 to 6.60 mol·kg −1 , respectively, from 298.15 to 353.15 K. The calculated solubility needs thermodynamic properties of the binary systems based on the water activity measurements. Therefore, the water activities of K 2 HPO 4 and Na 2 HPO 4 aqueous solutions were measured from dilute to the saturated solution, using the hygrometric method at different temperatures. The related thermodynamic properties of K 2 HPO 4 (aq) and Na 2 HPO 4 (aq) were evaluated by the development of ion-interaction model. The Gibbs energies of dissolution Δ G diss ∘ of K 2 HPO 4 (s) and Na 2 HPO 4 (s) and the solubility product were also determined at various temperatures. Graphical Abstract