Jelena Miladinović

Osmotic and activity coefficients of {yNaH2PO4 + (1 - y)Na2SO4}(aq) at the temperature 298.15 K

Abstract The osmotic coefficients of the mixed electrolyte solution { y NaH 2 PO 4 +(1− y )Na 2 SO 4 }(aq) have been measured by the isopiestic method, at the temperature T =298.15 K. The activity coefficients of NaH 2 PO 4 and Na 2 SO 4 were calculated by Scatchards neutral-electrolyte method and by Pitzer and Kims treatment for mixed-electrolyte solutions. The Scatchard interaction parameters are used for calculation of the excess Gibbs energy as a function of ionic strength and ionic-strength fraction of NaH 2 PO 4 . Also, the Zdanovskiis rule of linearity is tested.

Correlation of osmotic coefficient data for ZnSO4(aq) at 25°C by various thermodynamic models

The available literature data on the osmotic coefficient of ZnSO4(aq) at 25°C in the molality range from 0.1 to 4.3 mol-kg−1 and new experimental data from 1.2 to 2.9 mol-kg−1, at the same temperature, are presented. Selected values of the osmotic coefficient from all the data are analyzed using the Clegg-Pitzer-Brimblecombe model, the extended Pitzer model, and a semiempirical equation comprising a power series in molality added to the Debye-Hückel limiting law. The extended Pitzer equation and the Clegg-Pitzer-Brimblecombe equations give the best results in fitting the osmotic coefficient data. All three models are used to calculate ZnSO4 activity coefficients at 25°C in dilute solutions (<0.1 mol-kg−1) for comparison with published values.

Solubility in the ternary system CaSO4 + Na2SO4 + H2O at 298.15 K

The solubility in the ternary system, aqueous mixture of CaSO4 and Na2SO4, at T = 298.15 K comprises five different salts: calcium sulfate dihydrate, mirabilite, thenardite, glauberite and labile salt. Using the Extended Pitzer’s Ion Interaction model for pure and mixed electrolyte solutions and criteria of phase equilibria, predicted solubility behavior of salts was compared with experimental results from literature. The agreement between calculated and experimental solubilities was excellent in the ionic strength range up to 10.9062 mol kg−1.

Osmotic coefficient of the ZnCl2(aq) at T=298.15 K

Abstract The osmotic coefficient of ZnCl2(aq) has been measured at T=298.15 K by the isopiestic method over the range of molalities from (0.4 to 2 .4) mol · kg −1 with KCl(aq) as the reference solution. The available literature data on the osmotic coefficient of ZnCl2(aq) at T=298.15 K, and new experimental data were treated by the Clegg–Pitzer–Brimblecombe equation and the extended Pitzer’s equation. These equations were used to calculate the activity coefficient of ZnCl2 at T=298.15 K. The formation of the ZnCl+ complex has been taken into account by means of the Clegg–Pitzer–Brimblecombe equation.

Solubility in K+-Na+-Mg 4 2− aqueous solution at T = 298.15 K

In the salt solubility predictions for K+-Na+-Mg42− aqueous solution the treatment of thermodynamic data of three-component systems at T = 298.15 K involved the application of the Extended Pitzer’s ion-interaction model for the pure and mixed electrolyte solutions and criteria of phase equilibrium. Osmotic coefficients data of three-component systems were revised according to recently published parameters of the solutions NaCl(aq) and KCl(aq) that served as reference standards in isopiestic measurements. Parameters of the extended ion-interaction model of K2SO4(aq) are determined by treatment of experimental and predicted values of osmotic coefficient in supersaturated region obtained by the Zdanovskii-Stokes-Robinson rule. Results of salt solubility prediction were compared to experimental solubility data from literature. The agreement between calculated and experimental solubility data in the systems K2SO4 + MgSO4 + H2O, Na2SO4 + MgSO4 + H2O, and Na2SO4 + K2SO4 + H2O at T = 298.15 K, was excellent.

Thermodynamics of mixed and pure aqueous solutions of K2HPO4 at T = 298.15 K

Experimental results on isopiestic measurements for three ternary aqueous solutions of K2HPO4 with KCl, KBr, and KNO3 at T = 298.15 K were modeled with the Clegg–Pitzer–Brimblecombe equation based on mole-fraction-composition scale yielding appropriate mixing parameters, for the estimation of thermodynamic activities of solute components. The results for mean ionic activity coefficients of electrolytes in ternary solutions, calculated this way, are showing specific behavior depending on total ionic strength and ionic strength fractions of electrolytes. The activity coefficients of KCl in {yKCl + (1–y)K2HPO4}(aq) and of KBr in {yKBr + (1–y)K2HPO4}(aq) are changing consistently from the ionic strength and their ionic strength fractions contrary to activity coefficients of KNO3 in {yKNO3 + (1–y)K2HPO4}(aq). In addition, molality of K2HPO4 aqueous saturated solution, in equilibrium with K2HPO4 · 3H2O(cr), and appropriate osmotic coefficient at T = 298.15 K, were determined by the isopiestic method.