Isolation Of Caffeine From Tea (Chemistry)

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Isolation of Caffeine from Tea CHEM243A 2-23-11 Abstract: The purpose of this experiment was to isolate caffeine from a tea bag. Once isolated, the caffeine was purified using sublimation. The percent recovery was calculated to be 83.3%. The melting point of the original substance was 51ºC-139ºC. Since it was inaccurate, the melting point of another group’s sample was recorded. It was determined to be 219ºC-227ºC. Results: Percent recovery=100*(weight of pure/weight of impure) Weight of Crude Caffeine | Weight of Purified Caffeine | Percent Recovery | 0.018 g | 0.015 g | 83.33% | | Started Melting | Completely Melted | Our Sample | 51 | 139 | Other Group’s Sample | 219 | 227 | Since the melting point determined was so different from the known melting point of caffeine, there must have been impurities in the sample. This is also why some of sample melted immediately while the rest took much longer. This wide melting range also indicated impurities. Discussion: The procedure used to isolate the caffeine from a tea bag is very particular. The first step is to submerge the tea bag in hot water, much like when making tea to drink. This separates the soluble fraction from the insoluble cellulose, non-hydrolyzable, and tannins. This step is slightly different from brewing tea because only 10 mL of water is used. All of the water immediately absorbs into the bag and must be squeezed out. Brewing tea to drink requires much more water. The next step in isolation is to add dichloromethane. The purpose of this step is to separate the aqueous layer from the organic layer. This gets rid of the K-salts of gallic acid and glucose. The organic layer still contained caffeine and chlorophyll and any other organic compounds. The final step is to purify the caffeine from any impurities. Sublimation is the technique used. First, the vacuum is applied. Then ice

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