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 th e 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 Mg 2+ (aq) and the solid species Mg(OH)(2), (s), only. Independent measur ements have confirmed that [Mg(OH)](+) (aq) is a negligible ionic spec ies under the prevailing experimental conditions. Experimental evidenc e indicated that the solid species formed both rapidly and reversibly. The equilibrium quotients for brucite formation were determined for e ach 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 eq uation, and these data, together with some other literature data, comp ly with the equation log beta(12s)degrees = 2.49-(5847/T) where log be ta(12s)degrees is the logarithm of the formation constant of brucite a t zero ionic strength and T is the temperature in Kelvin.