ALUMINUM SPECIATION AND EQUILIBRIA IN AQUEOUS-SOLUTION .3. POTENTIOMETRIC DETERMINATION OF THE 1ST HYDROLYSIS CONSTANT OF ALUMINUM(III) IN SODIUM-CHLORIDE SOLUTIONS TO 125-DEGREES-C

The first molal hydrolysis quotient of aluminum(III) was measured potentiometrically from 25 to 125-degrees-C at 25-degrees intervals at ionic strengths of 0.1, 0.3, 1.0, and 5 mol - kg-1 with sodium chloride as the supporting electrolyte. The experimental method involved using a hydrogen-electrode concentration cell modified to compensate for any intrinsic potential offset between the two electrodes. The initial concentration of Al3+ was varied to test for the presence of multinuclear aluminum species while being kept to a maximum of 10(-3) mol . kg-1 to minimize their occurrence. Similarly, the maximum degree of hydrolysis of Al3+ reached in each titration was ca. 30%, after which polymerization and/or precipitation became apparent. The equilibrium quotients obtained in this study and selected values from the literature were fitted by an empirical equation incorporating a linear dependence of log K1,1 on the reciprocal temperature (Kelvins) over the range 10-200-degrees-C and three ionic-strength-dependent parameters. Comparisons are made between the results of this study and the literature values.