Experiment & Report
E X P E R I I M E N T &
R E P O R T
C H E M I I S T R Y H i i g h
Higher Chemistry e r r ( ( H C
E X T R A C T I I O N O F C A F F E I I N E F R O M T E A
INTRODUCTION
The active ingredient that makes tea and coffee valuable to humans is caffeine. Caffeine is an alkaloid; a class of naturally occurring compounds containing nitrogen and having the properties of an organic amine base (same family as cocaine, nicotine, morphine) . Caffeine is found in over 60 plant species. Caffeine is found naturally in tea and coffee beans with concentration levels between 2 and 5 %. Caffeine is a stimulant. Caffeine also has some undesirable side effects, such as an increase in the heart rate, nervousness, restlessness, and insomnia. One can become addicted to caffeine, resulting in physical dependence on this chemical.
Caffeine solubility in water
Temperature (ºC) Solubility of caffeine in water
(mg/cm 3 )
20 ~10
80 ~200
100 ~600
In this experiment we will extract caffeine from tea leaves using an aqueous solution of sodium
carbonate and ethyl ethanoate (ester). The sodium carbonate prevents the extraction of acidic compounds called tannins from the tea leaves. The basic property of alkaloids comes from the lone pair of electrons found on at least one nitrogen. The basic N in caffeine can be used to increase or decrease its water solubility. Acidic conditions will form the conjugate acid salt giving caffeine increased water solubility as a cation. On the other hand if caffeine is in a basic environment it takes the neutral form and is only somewhat polar.
Tannic acid
Caffeine is more soluble in the organic solvent ethyl ethanoate than in water, so we will extract caffeine into the organic solvent to separate it from glucose, tannins, and other water soluble compounds using a separatory funnel. Any water that remains in the organic solvent will be removed using a drying agent called sodium sulfate. We will then boil off the organic solvent to isolate unpurified (crude) caffeine.
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Experiment & Report Higher Chemistry
METHOD
1. Weigh 4 tea bags and place them in a 500 cm 3 beaker.
2. Add 250 cm 3 of water and 5 g of sodium carbonate (Na
2
CO
3
) to the beaker containing the tea and heat the mixture to boiling. The mixture must boil for 15 minutes. Watch it carefully to make sure that it does not boil over.
3. Allow the mixture to cool for 5 minutes, add ice directly to the beaker to cool the mixture to room temperature.
4. Remove the tea bags from the mixture and discard them, use a spoon to squeeze out all of the tea solution.
5. Add 50 cm 3 of ethyl ethanoate to the tea solution.
6. Pour your mixture into the separating funnel. Place the glass stopper in the funnel and gently tip the funnel upside down, making sure to hold the stopper in place. While the funnel is upside down, open the stopcock to release the pressure. (Warning: do not point the funnel at anyone). Close the stopcock and set the funnel back on the ring. The ethyl ethanoate (organic) layer is the upper layer and the water layer (aqueous) is the bottom layer. Once the layers have separated, open the stopcock to collect as much of the aqueous layer in a 600 cm 3 beaker as possible.
7. Then drain the solvent layer into a separate 600 cm 3 beaker and set aside. Pour the aqueous layer back into the separating funnel.
8. Add 50 cm 3 more ethyl ethanoate to the funnel. Gently invert it as described above, vent it, and collect the organic layer in the same 600 cm 3 beaker and then drain the organic layer into its collection beaker.
9. Carefully add 5 grams of sodium sulfate (Na
2
SO
4
) to the solution to remove any water present in the solution. Wait five minutes, and the solution should appear clear
(not brown and cloudy) if all of the water has been removed. Pre-weigh a clean, dry
250 cm 3 beaker with two boiling chips.
10. Using a funnel and filter paper, filter the liquid into the pre-weighed beaker.
11. Boil off the solvent by heat on a hot plate. Ethyl ethanoate boils at a relatively low temperature (77°C), so you do not have to apply a lot of heat (in other words don’t put the hot plate on high). Watch the beaker carefully as you boil it down to make sure you do not burn the caffeine.
12. Do not heat completely dry, leave in the fume cupboard until the following lesson to allow the last of the ethyl ethanoate to evaporate off.
13. Reweigh the mass of the beaker and calculate the mass of your caffeine.
HAZARDS
 Ethyl ethanoate is hazardous in case of ingestion, of inhalation. Slightly hazardous in case of skin contact (irritant, permeator), of eye contact (irritant). It is flammable.
 Sodium Carbonate hazardous in case of skin contact (irritant), of eye contact (irritant), of ingestion, of inhalation (lung irritant)
Wear goggles and immediately wash off any chemical spillages on the skin. Ethyl ethanoate should be kept in the fume hood. Room should be well ventilated. Ethyl ethanoate is flammable should be kept away from Bunsen flame and only heated using mantle.
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Experiment & Report
REPORT
Higher Chemistry
Q1) Explain why the solubility of caffeine in water increases with temperature.
Q2) Tannic acid is very soluble in water, looking at the structure of tannic acid, why do you think it is very soluble in water?
Q3) State two reasons why sodium carbonate was added to tea solution.
Q4) The ester used as a solvent in this experiment was ethyl ethanoate, what evidence from the experiment support the following statements: a) Ethyl ethanoate is less dense than water. b) Ethyl ethanoate us a non-polar solvent.
Q5) The drying agent, magnesium sulfate, was used to absorb any water still present in the non-polar solvent (ethyl ethanoate) layer. Drying agents are added to the solution of a compound that needs to be dried. The agents will easily pick up any extra water from the compound solution and become hydrated. The hydrated salts form clumps which can be filtered out or left behind during decanting resulting in a "dry" compound. What type of bonding allows magnesium sulfate to be used as a drying agent in this case?
Q6) Explain why the yield of caffeine produced will be lower than the caffeine present in the tea to begin with.
Q7) Which layer in the separating funnel would you expect to find glucose, explain your answer.
Read page 183-189 in your Higher Chemistry textbook on chromatography techniques that could be used to improve extraction technique. (answer study question 1 and 2)
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