Infrared Spectra of Aluminum Salt Solutions

Aluminum salt solutions activate metallic aluminum surfaces at different rates. The objective of this investigation was to attempt to establish whether or not structural differences at the molecular level could account for the chemical reactivity. The infrared spectra of various concentrations of aluminum chloride, aluminum nitrate, aluminum perchlorate, and aluminum sulfate were measured. The spectra included several general features: (1) a broadening of the OH stretching band of water, (2) a splitting of the OH stretch of water into several absorption bands, (3) the emergence of a new absorption band at 2400 cm −1 (related to dimer formation), (4) splitting of the NO 3 − absorption band at 1370 cm −1 (5) occasional splitting of the OH bending mode of water, (6) no direct evidence of anion-cation interaction for AlCl 3 , Al(CIO 4 ) 3 , and Al 2 (SO 4 ) 3 . In general, there was no difference at the molecular level between these aluminum salt solutions that would account for differences in chemical reactivity.