Hydrolysis Studies and Quantitative Determination of Aluminum Ions Using 27Al NMR. An Undergraduate Analytical Chemistry Experiment

Abstract

This article describes a novel experiment focused on metal ion hydrolysis and the equilibria related to metal ions in aqueous systems. Using 27Al NMR, the students become familiar with NMR spectroscopy as a quantitative analytical tool for the determination of aluminum by preparing a standard calibration curve using standard aluminum solutions in dilute nitric acid keeping the aluminum in the hexaaquoaluminum ion form, Al(H2O)63+. The technique has a large linear dynamic range, and in this experiment it ranges from 10 to 1000 ppm. Once the quantitative technique is validated, the goal of the experiment is to investigate the hydrolysis of Al3+ ions in aqueous solution by determining the concentration of the Al(H2O)63+ ion by 27Al NMR for a series of solutions with the same total concentration of aluminum but at various pHs ranging between 1.0 to 4.5. This experiment is also suitable for an instrumental analysis or inorganic chemistry course.