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Journal of the Mexican Chemical Society

Print version ISSN 1870-249X


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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