The Equilibrium Constant for the Formation of Al2(OH)24+ in Aqueous Solutions

The equilibrium constant for the formation of the aluminum hydroxy dimer, Al2(OH)24+, was calculated from measured values of pH and the concentrations of the dimer and trivalent aluminum in aqueous solutions at 25 °C. The concentrations of Al2(OH)24+ was determined by a method based on its rate of reaction with an 8-hydroxyquinoline – sodium acetate solution. Experiments were made with various concentrations of aluminum and different ionic strengths. With an ionic strength of 0.06, the equilibrium constant was 10−7.42 and increased with decreasing ionic strength. The negative log of the equilibrium constant when the ionic strength approaches zero was estimated to be 6.95 ± 0.05.