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

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Published thermodynamic data yielding the osmotic coefficients, relative apparent molar enthalpies, and apparent molar heat capacities of Mg(NO3)2(aq) have been collected, recalculated consistently, and critically assessed. The more reliable of these data have been used to evaluate the parameters of the standard three-parameter form of Pitzer's ion-interaction model to higher molalities than previously available, along with the parameters of Archer's four-parameter, extended ion-interaction model at 298.15 K. Published experimental thermodynamic data were essentially represented equally well by these two models, provided that the exponential coefficient α1 of the standard Pitzer model is fixed at the optimum value of α1 = 1.55 kg1/2·mol-1/2 rather than the traditional value of α1 = 2.0 kg1/2·mol-1/2. The use of the standard Pitzer model with this modified α1 value is recommended for Mg(NO3)2(aq). In addition, an empirical equation is given for the variation of the water activity of a saturated solution with temperature, from 273.54 to 328.20 K, with Mg(NO3)2·6H2O(s) as the solid phase.