NAME: Kimberly Nguyen Experiment 3. Extraction and Isolation of Caffeine from Tea Leaves I.
INTRODUCTION The purpose of this experiment is to isolate caffeine from tea bags through solid­liquid extraction, liquid­liquid extraction involving a weak base and salts, and purification through sublimation. Solid­liquid extraction uses water to extract some aqueous particles, such as caffeine, saponins, tannins, proteins and pigments. In liquid­liquid extraction, using a weak base cleaves tannins into more polar counterparts, while salting out allows for caffeine to be more soluble in the organic layer. Sublimation is the final purification process that makes use of the phase properties of caffeine. Caffeine sublimes at conditions unlike its contaminants, so reducing the pressure and raising the temperature to around 160 degrees celsius nearly perfectly isolates caffeine from impurities. II.
DATA AND CALCULATIONS (i) Mass of Crude Caffeine:
0.221 g (ii) Appearance of Crude Caffeine (color, etc.): (iii) Melting Point of Crude Caffeine:
White, Powdery 221.0 o C d (Calibrated) (iv) Mass of Sublimated Caffeine: 0.221 g (Instructed to use crude value) (v) Appearance of Sublimated Caffeine (color, etc.): (vi) Melting Point of Sublimated Caffeine:
Foggy 233.1­232.8 o C (vii) % Sublimated Caffeine in Dry Tea Leaves: 0.221 g
3.0258 g
= 7.30% DATA ANALYSIS AND CONCLUSIONS The mass of crude caffeine was 0.221 g with no clear melting point. Instead, the sample appeared to decompose at around 218.2 o C. The mass of sublimed caffeine is for all calculation purposes 0.221 g, but the actual mass was unable to be obtained, due to its thin and spread out sublimation on flask walls. The sublimed caffeine had a foggy appearance in the flask. The melting point of the sublimed caffeine was 230.3­230.7 o C, indicating that there was in fact some impurities within crude caffeine, since it did not appear to melt at all. The percent of purified caffeine in dry tea leaves was 7.30%, indicating little caffeine content as well as instances of generic laboratory errors such as losing caffeine in tea leaves, liquid extractions, flask walls, and instruments. Sublimation is a powerful purification technique, generally better than recrystallization when it comes to purification; however, limitations can include difficulty obtaining analytical yield, ineffectiveness due to distance of cold finger and flask bottom, and the pressure and temperature not controlled enough to ensure that other impurities do not sublime as well.