Lab Report - Extraction of Caffeine from Tea PDF

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Extraction of Caffeine from Tea...

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Lab Report

Experiment: Extraction of Caffeine from Tea Objective: The objective of the experiment is to learn how to extract caffeine from tea, using basic organic chemistry techniques. Materials: - Tea leaves - 400 mL beaker - Calcium Carbonate - Water - Hot Plate - Stirring Rod - Vacuum Filtration Apparatus - Filter Paper - Separatory Funnel - Supporting Ring - Dichloromethane

Procedure: Placed 9-10g of tea leaves in a 400mL beaker. Added 4.8g of Calcium Chloride and 125mL of water over the tea leaves. Using a hot plate, it was boiled for 15 minutes. The mixture was left to cool to 55C. With a No. 54 paper filter and the vacuum filter apparatus the solution was purified. Next it was divided in 2 portions. The solution was placed in an ice bath. Following this, a separatory funnel was used to pour the mixture in. An amount of 15 mL of dichloromethane was added. Two layers appeared, one the aqueous and one the organic layer. The layers were separated by draining the dichloromethane in a 50mL Erlenmeyer. An additional 15mL of dichloromethane was added into the tea solution in the separatory funnel. The funnel was inverted and opened so the gases would escape. Again, the layers separated, and the organic layer was drained in the same 50mL Erlenmeyer used before. Next, the tea leave solution was poured into a beaker. The organic layer which was in the 50mL Erlenmeyer was poured into the separatory funnel and 20mL of water were added. Like before, the separatory funnel was inverted a few times and it was opened so the gases would escape. When the water and dichloromethane separated the latter was drained into the 50mL Erlenmeyer. A drying agent, magnesium sulfate, was added into the Erlenmeyer to remove any water in the dichloromethane and the Erlenmeyer was corked close. The solution was left to sit for 10 minutes. To filter out the drying agent a conical funnel and filter paper were used. Last, the dichloromethane was evaporated on a steam bath until a green residue formed in the bottom. Results: The green residue formed in the round-bottom flask. The weight of the round-bottom flask empty was 54.066g.

The weight of the round-bottom flask with the green residue was 54.060g. Calculations: We couldn’t calculate the yield of the procedure because of an error in the weighting. Weight of empty ball flask 54.066g

Weight after steam bath 54.060g

Difference - 0.006g

Discussion: The basic property of caffeine comes from the lone pair of electrons found around the nitrogen. The nitrogen present controls solubility. Caffeine is soluble in water at approximately 2.2 mg/ml at 25°C, 180 mg/ml at 80° C, and 670 mg/ml at 100°C. This is why the tea was boiled with water, because the caffeine is soluble in it. Also, because water is present, it’s possible to separate inorganic from organic compounds since organic substances are immiscible in water. After the heat bath, the aqueous tea solution was cooled to 15°C before adding the dichloromethane because the dichloromethane would have evaporated, and caffeine would not have been extracted correctly. During the extraction the emulsions or solid insoluble materials like cellulose were separated from caffeine and tannins. The reason why salt (NaCl) was added to the aqueous layer to help break up any emulsion is because a difference in solubility must occur to separate the tannins into the aqueous layer. Sodium carbonate is basic, but Tannins are acidic. Because of this, the sodium carbonate acts as a nucleophile and the tannin as an electrophile. The nucleophile attacks electrophile and reacts as an acid/base reaction, getting rid of the emulsions. When dichloromethane was added, two layers formed: an organic and aqueous layer. Because Dichloromethane is denser than water, it is located at the bottom of the separatory funnel. It has a density of 1.325 g/m. The concentration of the solutes in the organic layer contributes to the fact that it is below the aqueous layer. Therefore, a high concentration of caffeine is found and small amounts of water. A drying agent (anhydrous CaCl2) was added to remove the water in the organic layer so that a pure sample of caffeine could be retrieved. The CaCl2 stopped clumping together when excess water was removed. To remove the dichloromethane, the solution was transferred to a ball flask and placed in a steam bath so that the solvent would evaporate and leave a green residue. When the weighting of the ball flask occurred, an error was made since the first weight was more than the second one which had the green residue in the flask. There could have been an error with the balances, or the ball flask could not have been dried enough after washing. For this reason, we couldn’t calculate the amount of caffeine recovered neither the yield of it.

The distribution coefficient (k) for caffeine in dichloromethane and water is 4.6. Assuming that the tea solution is 100mL and contains 0.30g of caffeine.

After single extraction with 15mL, 0.178g of caffeine is in the water and 0.122g is in the dichloromethane.

( 0.30 g−x ) (15mL ) 4.6= x /( 100 ml ) 4.6=

(30−100 x ) 15 x X= 0.178g of caffeine in the water (0.30-0.178g) = 0.122g in dichloromethane

After two extractions with 15mL each, 0.105g of caffeine is in the water and 0.195g is in the dichloromethane. 4.6=

(0.178 g− x)/(15 mL ) x ( ) 100 mL 4.6 = (17.8 – 100x) / (15x) X = 0.105g of caffeine in the water (0.178g – 0.105g) = 0.073g in dichloromethane Total caffeine in dichloromethane is 0.195g

Using K after a single extraction using 30mL, 0.126g of caffeine is in the water and 0.174g is in the dichloromethane. 4.6=

4.6=

(0.30 g−x)/(30 mL) x 100 mL 30−100 x 30 x X = 0.126g of caffeine in the water 0.30 – 0.126g =0.174g in dichloromethane

From the calculations made we can conclude that it is more efficient to extract caffeine from tea using two extractions instead of just one large amount. More caffeine was separated from water when doing two extractions (0.195g), using 30mL once separated less caffeine from water (0.174g)....