Enthalpies of the hydrolysis reaction of Al3+ ion between 25 e 150 °C

The heat produced when NaOH is added to Al3+ (m(Al)0 congruent-to 0.03 mol kg-1) in water has been measured in the range 25-150-degrees-C. These calorimetric data are consistent with the chemical model proposed by Mesmer and Baes which considers two polynuclear and one polymeric hydrolytic species of aluminium ion. Other models which consider, in addition, the presence of mononuclear species might be valid as well, while models involving these latter species alone should be ruled out, at least in the experimental conditions adopted in this work. A simple equation is proposed for calculating the enthalpy of formation of hydrolytic species of aluminium from the measured value of the average enthalpy for addition to aqueous Al3+ of one mole of hydroxy groups.