Hydrolysis of magnesium(II) at elevated temperatures

A potentiometric titration technique utilising a a hydrogen-electrode concentration cell was applied to study the hydrolytic behaviour of the magnesium(II) ion in 0.10 and 1.0 mol kg(-1) sodium chloride at 60, 100, 150 and 200 degrees C. Data analysis indicates the presence of Mg2+ (aq) and the solid species Mg(OH)(2), (s), only. Independent measurements have confirmed that [Mg(OH)](+) (aq) is a negligible ionic species under the prevailing experimental conditions. Experimental evidence indicated that the solid species formed both rapidly and reversibly. The equilibrium quotients for brucite formation were determined for each temperature and ionic strength investigated and the corresponding enthalpy and entropy of formation calculated. Formation constants have also been calculated at zero ionic strength using the Debye-Huckel equation, and these data, together with some other literature data, comply with the equation log beta(12s)degrees = 2.49-(5847/T) where log beta(12s)degrees is the logarithm of the formation constant of brucite at zero ionic strength and T is the temperature in Kelvin.