EXPERIMENT NO. 1

ISOLATION OF CAFFEINE FROM TEA

I. OBJECTIVES To gain experience in using extraction as a method of separation To assemble and use a simple distillation setup in the separation of volatile

substances from non-volatile substances To determine the boiling point of a liquid sample To isolate caffeine from tea and gain experience in chemical laboratory

manipulation of plant materials

II. DATA AND RESULTS

Weight (g)Tea 20 gSodium carbonate 12.5 g

Boiling point of Chloroform: 60° CPre-weighed evaporating dish- 51.3522Caffeine: 51.3826-51.3522= 0.0504 gTheoretical: 0.7080 g of caffeine per tea bagPercentage Yield- 0.0504 g/ (0.7080 x 10 tea bags) x 100%= 1.42 %

III. DISCUSSION OF RESULTS

In the solid-liquid extraction, the soluble compounds of the solid sample (tea) are extracted by the solvent which is the water. When 20 g of tea were boiled, the hot water swells the tea to release caffeine and other compounds such as tannin. In order to prevent the extraction of tannin, 12.5 g of sodium carbonate were added. This reacts with tannin to form insoluble salt. Thus tannin and other solid components were left on the beaker while caffeine and water were collected as filtrate after decantation

In the liquid-liquid extraction, chloroform is used as the solvent. In this process, the compounds are separated based on their solubilities into two immiscible liquids such as water and chloroform. Since caffeine dissolves in chloroform, two immiscible liquids have appeared namely, the chloroform layer and the aqueous layer. Since they are immiscible they can be easily separated by letting the aqueous layer out of the separatory funnel. After adding additional amount of chloroform, more aqueous layer was formed and separated. With shaking and swirling of the separatory funnel, bubbles appeared. These are called emulsions. An emulsion is a mixture of two immiscible liquids. When tannins are converted to their salts, they become an ionic surfactant. These causes the materials that don’t dissolve in water to form an emulsion with water. This emulsion can be minimized by careful

handling and swirling of the separatory funnel. Sodium sulphate was also added in order to remove traces of water left with the chloroform layer.

To separate caffeine from chloroform, distillation was done. Their differences in volatility and boiling points made them easy to separate by simple distillation. Chloroform has a boiling point of 60° C which is lower than caffeine. The solution started to boil vigorously within 54° C and constantly boiled at 60° C for several minutes. The chloroform evaporated first so it was the one that was collected as the distillate and the remaining liquid in the distilling flask contains the caffeine. The remaining liquid in the distilling flask was further heated until all the chloroform evaporated leaving caffeine crystals.

An empty evaporating dish was weighed and it weighs 51.3522 g. After the caffeine crystals were isolated, the evaporating dish containing the crystals was weighed again. It weighed 51.3826 g . By subtracting the weight of the crystals together with the evaporating dish and the evaporating dish we can get the weight of the caffeine that was extracted. Its weight is 0.0504 g. Thus the percentage yield of caffeine in the tea is 1.42 %. The small amount of caffeine crystals that are obtained is attributed to some errors occurred during the experiment. In our first trial of liquid-liquid extraction, the solution that we extracted evaporated so in this experiment we only used the solution that we extracted from the 2nd trial that is why the amount of caffeine crystals that we extracted is half of the actual expected amount of the extracted caffeine.

IV. CONCLUSION

In order to isolate caffeine from tea, different types of extraction methods were done. The solid-liquid extraction extracted soluble components such as caffeine from tea with water as the solvent. In the liquid-liquid extraction, chloroform was used to dissolve caffeine and to separate it from water. Chloroform and caffeine are then subjected to distillation for separation due to the difference on their boiling points. Since chloroform has lower boiling point, it evaporated faster. The remaining liquid was then heated evaporating the chloroform and leaving the caffeine crystals. Out of 20 g of Tea, only of caffeine was obtained.

The small amount of caffeine crystals that are obtained are due to some errors occurred during the experiment. It may be personal or instrumental errors. Our personal errors include letting the solution evaporate and carelessness in handling chemicals that we spilled some of the chemicals. In order to prevent or minimize these errors, it is recommended that the experimenters must do the procedures carefully and systematically. Always remember that proper handling of chemicals, proper weighing of samples and proper ways to transfer liquids to another container.

V. QUESTIONS

A. Discuss briefly the role of the following in the isolation of caffeine:1. Sodium carbonate- it prevents the extraction of tannin. It reacts with tannin and

forms an insoluble salt thus removing it from the solution2. Sodium sulphate- It acts as drying agent because it removes any water that remains

in the chloroform layer.

B. Give at least three characteristics of chloroform that make it a good extracting solvent for caffeine.

Chloroform is a good extracting solvent fro the isolation of caffeine because caffeine dissolves in it, it is immiscible with water and it has lower boiling point that caffeine.

C. How efficient is the extraction of tea leaves containing 1 g of caffeine with two 30-mL portions of chloroform over that of a single step extraction (K25° C = 8.38)?

D. What are emulsions? Why do they form during extractions? How are they minimized?Emulsion is a mixture of two immiscible liquids. One liquid (the dispersed

phase) is dispersed in the other (continuous phase). When tannins are converted to their salts, they become an ionic surfactant. These causes the materials that don’t dissolve in

water to form an emulsion with water. This emulsion can be minimized reducing the energy input through slow and careful shaking and swirling of the separatory funnel.

E. Why is it necessary to remove a stopper from a separatory funnel when liquid is being drained from it through a stopcock?

It is necessary to remove the stopper from a separatory funnel in order for the liquid to continually flow out. Removing the stopper would release the pressure so the liquid will flow continuously. When stopper is not removed, the liquid will not drain out no matter how you manipulate the stopcock.

VI. REFERENCES Microsoft Encarta 2009 “Isolation of Caffeine from Tea.”Retrieved November 23,2010.http://science.

csustan.edu/almy3012/caffeine.htm “Liquid-Liquid Extraction” Retrieved November 23,2010.http://en.wikipedia.o

rg./wiki/Sol ven_extraction “Solid-liquid extraction.” Retrieved November 23,

2010.http://209.85.175.104/search?q=cache:RGNjHy_IUQJ:www.iq.uva.es/separation/archivos/SkriptumExtracton

Brown, T.E, Lemay, H.E, Bursten, B.E, Burdage ,J.R. Chemistry the Central Science 9th edition Pearson Education.Singapore.2004.