Isopiestic determination of the osmotic and activity coefficients of the { y Mg(NO 3 ) 2 + (1 − y )MgSO 4 }(aq) system at T = 298.15 K

Isopiestic Determination of Osmotic and Activity Coefficients of the {yNaH2PO4 + (1 – y)Na2HPO4}(aq) System at T = 298.15 K

“…As seen in Figure 2, the osmotic coefficients for the {yNaH 2 PO 4 + (1 − y)Na 2 HPO 4 }(aq) system, derived from the study of Scharge et al, 13 are systematically lower than those obtained in the present investigation. A similar situation occurs for the chemically similar {yKH 2 PO 4 + (1 − y)K 2 HPO 4 }(aq) system as described by Ivanovićet al 11 Scharge et al 12 dried their source chemicals at T = 378 K and prepared their solutions by mass using the presumed anhydrous material. In contrast, in our studies, the molalities of the stock solutions were standardized by determination of the phosphate contents of the solutions by gravimetric analyses.…”

“…Table 6 reports the mixing parameters for a variety of constraints: both with and without the higher-order electrostatic mixing terms being included and with and without being constrained by θ ij values fixed at those obtained from the chemically similar {yK 2 HPO 4 + (1 − y)KH 2 PO 4 }(aq) system. 11 Examination of the standard uncertainties for the variants of the model with either one or two mixing parameters indicates that the model with higher-order electrostatic mixing terms and the single adjustable mixing parameter s θ H 2 PO 4 ,HPO 4 is as accurate or more accurate than models with two mixing parameters and is our selected model. In Figure 9 are shown differences between experimental and calculated osmotic coefficients for the system {yNaH 2 PO 4 + (1 − y)Na 2 HPO 4 }(aq) at T = 298.15 K calculated using the extended Pitzer model with the parameter s θ H 2 PO 4 ,HPO 4 = −0.0017 kg•mol −1 with higher-order electrostatic terms, with standard uncertainty of the fit being u(ϕ) = 5.3 × 10 −4 .…”

“…Ivanovićet al 11 pointed out that anhydrous K 2 HPO 4 (s) is quite hygroscopic and can even deliquesce in the presence of atmospheric moisture and is therefore not a satisfactory weighing form for gravimetric preparation of solutions. Moisture absorption results in an apparent mass for "K 2 HPO 4 ", which is higher than the correct value and will thus yield calculated molalities of the solutions that are too large when the presence of this absorbed water is not recognized.…”

“…To provide some of the needed but unavailable thermodynamic information about complex aqueous mixtures containing phosphate salts, we 4 measured and reported isopiestic results at T = 298.15 K for the monohydrogen phosphate salt K 2 HPO 4 (aq) over a wide molality range extending to the oversaturated solution molality of 13.939 mol•kg −1 and for the mixture system {yKCl + (1 − y)K 2 HPO 4 }(aq), 5 followed by isopiestic measurements on the mixture systems {yKNO 3 + (1 − y)K 2 HPO 4 }(aq), 6 {yKBr + (1 − y)K 2 HPO 4 }(aq), 7 {yK 2 SO 4 + (1 − y)K 2 HPO 4 }(aq), 8 {yNa 2 HPO 4 + (1 − y)K 2 HPO 4 }(aq), 9 {yNaH 2 PO 4 + (1 − y)KH 2 PO 4 }(aq), 10 and {yK 2 HPO 4 + (1 − y)KH 2 PO 4 }(aq). 11 Some additional isopiestic measurements have been reported for binary phosphate solutions and their mixtures by Scharge et al 12,13 Furthermore, the need for reliable and precise data on the thermodynamic properties of aqueous solutions of alkali metal hydrogen phosphates and dihydrogen phosphates, as well as their mixtures, was emphasized. To extend the thermodynamic database, we now report measurements of the osmotic coefficients for the aqueous ternary system with HPO 4 2− (aq) and H 2 PO 4 − (aq) ions in equilibrium with the Na + (aq) ion and present the results in this paper.…”

“…Our previous studies on ternary solutions included the common-anion systems {yNa 2 HPO 4 + (1 − y)K 2 HPO 4 }(aq) and {yNaH 2 PO 4 + (1 − y)KH 2 PO 4 }(aq) 9,10 and the common potassium cation system {yK 2 HPO 4 + (1 − y)KH 2 PO 4 }(aq). 11 Thus, together with these three previous studies, we have now reported isopiestic measurements for all of the aqueous two salt common-cation and common-anion mixtures involving NaH The molality of the Na 2 HPO 4 (aq) stock solution was determined gravimetrically in triplicate using the method wherein the HPO 4 2− (aq) ions were precipitated as the sparingly soluble MgNH 4 PO 4 and then calcined at T = 1273 K to form Mg 2 P 2 O 7 (Schmitz's method). 14 The molality of the NaH 2 PO 4 (aq) stock solution was determined according to the suggestion of Childs et al, 15 where three solution aliquots were first dried at the temperature 393.15 K, where the initial residue is a hydrate NaH 2 PO 4 • xH 2 O(s).…”