摘要：Among soft drinks commercialized in Brazil, the one from guaraná seeds (Paullinia cupana) is very popular, ranking second in volume of consumption. Guaraná has the highest caffeine concentration in plants; its extraction with chloroform from aqueous solution is feasible using a relatively simple experimental protocol. Because of the commercial importance of this soft drink, and the health-related aspect of (stimulant) caffeine, we developed a project for high-school students on the extraction and analysis of caffeine from guaraná powder. In this three-step project, the students did- in their school- a literature survey on the presence of caffeine in beverages, foods and other consumer products. In the second step, they visited the laboratories of the Institute of Chemistry of the University of São Paulo (ChemUSP) where they extracted caffeine with CHCl3 from the aqueous solution obtained by treatment of guaraná powder with HCl, followed by filtration and alkalization. Using melting point and thin-layer chromatography, they checked the purity of the isolated caffeine. Finally, they determined its concentration by Uv-Vis spectroscopy. We used this simple, safe and low cost experiment to discuss several important concepts, e.g., acids and bases, solvent extraction, purity determination by simple physical method, and quantitative analysis by spectroscopy. The students evaluated this project positively.
关键词：High school; Chemistry of beverages; Guaraná; Caffeine; Solvent extraction; Uv-Vis
