Preparation and Heat of Formation of a Magnesium Oxysulfate
- 1 November 1964
- journal article
- Published by National Institute of Standards and Technology (NIST) in Journal of Research of the National Bureau of Standards Section A: Physics and Chemistry
- Vol. 68 (6) , 645-650
- https://doi.org/10.6028/jres.068A.064
Abstract
Magnesium oxysulfate, 3Mg(OH)2·MgSO4·8H2O, was precipitated from metastable aqueous solutions of MgO in MgSO4. The compound forms in solutions containing 12 percent or more of MgSO4, and remains unchanged in solutions containing 10 percent MgSO4, but at lower concentrations is converted to Mg(OH)2. Magnesium hydroxide is not converted to the oxysulfate by nearly saturated MgSO4 solutions in times up to three years. The solubility of the oxysulfate is given in the form of a plot of the basicity and MgSO4 content of magnesium sulfate solutions. The heat of solution of the oxysulfate compound in HCl·26.61H2O (2.000 normal at 25 °C) is 68.94 kcal/mole with a standard deviation of 0.23 kcal/mole and its heat of formation from Mg(OH)2, MgSO4·7H2O, and liquid water is ΔH=2.11 kcal/mole. The corresponding heat of formation from the elements is ΔHf°=-1537.9 kcal/mole.Keywords
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