Resumen de Distinguishing Calcium Carbonate from Calcium Sulfate Dihydrate by Instrumental Methods. A Set of Laboratory Experiments for Analytical Chemistry and Spectroscopy
Eugenio Garribba, Giovanni Micera, Angelo Panzanelli, Liliana Strinna Erre, Giovanna Stara
A project is proposed in which instrumental techniques are used to identify and characterize calcium sulfate and calcium carbonate or materials based on these compounds. The project involves thermogravimetry, IR and NIR vibrational spectroscopy, and X-ray fluorescence. Thermogravimetry measures the weight loss of the samples upon controlled heating and determines both water content and residue. FTIR spectra in the middle IR region are of particular interest. Because of solid-state effects, the theoretical interpretation requires knowledge of the symmetry of the molecules and the space group of the crystal. NIR spectra introduce the students to the analysis of nonfundamental vibrations and prove the presence of water in CaSO4·2H2O. X-ray fluorescence spectra, obtained on a homemade EDXRF instrument, discriminate CaSO4·2H2O from CaCO3 on the basis of the K lines of S and Ca. The lab sequence is very stimulating and provides a solid introduction to a variety of instrumental and spectroscopic methods, including their theoretical background. Although the project is designed for several techniques, each of the experiments may be used in a stand-alone manner.
