Studies on the Vapor Pressure—Temperature Relations and on the Heats of Hydration, Solution and Dilution of the Binary System Magnesium Nitrate—Water

Review of the Thermodynamic Properties of Mg(NO3)2(aq) and Their Representation with the Standard and Extended Ion-Interaction (Pitzer) Models at 298.15 K

“…Values of φ from the studies of Ewing et al 28 and of Chernykh et al 27 are reasonably consistent within the ∆φ ≈ ((0.02 to 0.05) imprecision typical of their measurements, although some of their φ values have significantly larger deviations. This imprecision is significantly larger than the imprecision for φ observed for the more consistent isopiestic results at 298.15 K. However, the vapor pressure results from Mashovets et al 30 yield φ values at 323.15 K that are lower than those from the other two studies 27,28 by ∆φ ≈ 0.1 to 0.2 at the higher molalities and are lower by ∆φ ≈ 0.6 at the lowest molality, which is a significantly large discrepancy. Ewing et al 28 made a single vapor pressure measurement at 298.15 K for an unsaturated solution of known molality, which yields an osmotic coefficient of φ ) 2.452 at 4.870 mol‚kg -1 ; this value is higher by ∆φ ≈ 0.1 (4%) compared to the results from more consistent isopiestic studies.…”

“…d Seven experiments were carried out for saturated solutions involving Mg(NO3)2‚2H2O(s) as the solid phase. 28 Twenty nine additional vapor pressure measurements involved solutions with Mg(NO3)2‚6H2O(s) as the solid phase, but only the 8 experiments on the ascending solubility branch were reanalyzed. Freezing temperature measurements were also reported by Ewing et al, 37 at various temperatures, for solutions with several different Mg(NO3)2‚xH2O(s) species as the equilibrium solid phases, where x ) 9, 9 + 6, and 6. e The concentrations of these studies were reported in units of mol‚L -1 .…”

“…However, the water vapor pressures assessed by Wexler and Greenspan 52 were selected instead because they were reported for both the IPTS-48 and IPTS-68 temperature scales. Unfortunately, none of the authors [28][29][30]32,33 of the direct vapor pressure studies for Mg-(NO 3 ) 2 (aq) identified which temperature scale was used for their measurements. We therefore assume that the temperature scale used was the international temperature scale that was generally accepted when these studies were published.…”

“…We searched the published literature and located 10 articles that reported isopiestic vapor pressure measurements for Mg(NO 3 ) 2 (aq), [18][19][20][21][22][23][24][25][26][27] several studies that reported the results from direct water vapor pressure measurements, [28][29][30][31][32][33] and four studies reporting freezing temperature measurements. [34][35][36][37] There are also three published studies that report enthalpies of dilution or relative apparent molar enthalpies of Mg(NO 3 ) 2 (aq), 28,38,39 two determinations of the enthalpy of solution of Mg(NO 3 ) 2 ‚6H 2 O(cr) at 298.15 K, 28,40 and two determinations of the heat capacities of Mg(NO 3 ) 2 -(aq).…”

“…We searched the published literature and located 10 articles that reported isopiestic vapor pressure measurements for Mg(NO 3 ) 2 (aq), [18][19][20][21][22][23][24][25][26][27] several studies that reported the results from direct water vapor pressure measurements, [28][29][30][31][32][33] and four studies reporting freezing temperature measurements. [34][35][36][37] There are also three published studies that report enthalpies of dilution or relative apparent molar enthalpies of Mg(NO 3 ) 2 (aq), 28,38,39 two determinations of the enthalpy of solution of Mg(NO 3 ) 2 ‚6H 2 O(cr) at 298.15 K, 28,40 and two determinations of the heat capacities of Mg(NO 3 ) 2 -(aq). 41,42 Although not all of these published studies are reliable, enough reliable data are available to permit the parametrization of the standard Pitzer ion-interaction model [12][13][14] at 298.15 K to much higher molalities than done previously and to evaluate the parameters of the extended ion-interaction model of Archer.…”