Abstract

ROJAS-HERNANDEZ, Alberto et al. Equilibrium Constants Determination of the Species Formation in the Al(III)-H₂O System by Integration of ²⁷Al-NMR Signals and Fitting with Species Fractions. J. Mex. Chem. Soc [online]. 2008, vol.52, n.1, pp.47-53. ISSN 1870-249X.

A quantitative methodology to determine formation constants that takes into consideration the ²⁷Al-NMR signals of Al(III)-H₂O systems has been analyzed, where area fractions beneath the peaks recorded were associated with the corresponding species fractions. The values of the formation constants were compared with the model obtained by potentiometric studies. In agreement with previous reports, the -log*β values obtained by NMR and potentiometry, at 0.020 M ≤ [Al(III)]_total ≤ 0.500 M are 12.96 ± 0.02 for Al(OH)₃, 13.50±0.02 for Al₃(OH)₄⁵⁺, and 109.70±0.09 for Al₁₃(OH)₃₂⁷⁺, by assuming that Al(OH)²+ has a value of 5.29. Additionally the equilibrium constant values obtained allowed fitting of the conductimetry titrations in the 6.00(10-³) M ≤ [Al(III)]_total ≤ 0.120 M. The algorithm presented in this work gives a support to establish that the area fractions of NMR signals are proportional to the species concentration fractions.

Keywords : ²⁷Al-NMR; hydrolysis of Al³⁺; formation constants; potentiometric titrations; conductometric titrations.

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