Infrared Examination of the Transformation of Barium Sulfate into Barium Carbonate. An Inorganic Infrared Qualitative and Quantitative Experiment

Student experiments and lectures on infrared spectroscopy are generally concerned with the investigation of organic materials. Since experiments on inorganic materials are limited, students are generally unaware of the value of infrared spectroscopy in this area. This experiment provides an interesting pedagogical exercise that not only demonstrates the value of infrared spectroscopy in the investigation of inorganic systems, but also visually illustrates a procedure used in classical wet chemical qualitative analysis for sample preparation. In classical qualitative analysis, a water or acid insoluble sample, such as barium sulfate, can be transformed into species suitable for detection by boiling in a solution of sodium carbonate. The sulfate ion, now in solution, can be qualitatively detected and the barium ion, after acid dissolution of the barium carbonate, can be detected. The extent of the transformation depends on the reactant concentrations, the reaction temperature and time, and the relative solubility products. Since both barium sulfate and barium carbonate contain infrared-active polyatomic anions that exhibit characteristic non-interfering absorption bands, infrared spectroscopy is an ideal and convenient way of qualitatively and quantitatively following the process of the transformation. The equilibrium constant, the influence of time, temperature, and reactant concentrations on the extent of reaction can be determined.