Introduction:
Caffeine is a stimulant that can be found in tea, coffee, cocoa and cola drinks. It stimulates the brain and the central nervous system, so that a person feels less tired and more alert.
However, an overdosage may result in rapid heartbeats, hallucinations and stomach ulcers. Psychological dependence may also develope. And a person suffers from headaches, irritability and palpitations as withdrawal symptoms.
Caffeine is readily soluble in trichloromethane and thus can be extracted from tea using the method of solvent extraction.
Procedure:
Place 5g of tea leaves into a 250ml beaker and add 200ml of boiling water.
Allow to steep for 5 minutes.
Add 3ml of saturated zinc acetate solution to precipitate the tannis.
Filter the solution. Test the filtrate for complete precipitation of the tannis with a few drops of zinc acetate solution.
Add a few drops of dilute sulphuric acid to remove any lead ions in the tea. Both lead and tannis interfere in the extraction of caffeine and have to be removed.
Filter the solution again.
Extract the filtrate with 50ml of trichloromethane in a seperating funnel.
Invert the funnel several times, removing the stopper occasionally to allow the gas to escape. Continue for about 2 minutes and leave to stand overnight. Do not shake the seperating funnel vigorously or an emulsion will form.
Run off the clear trichloromethane layer into a clean, dry, weighed beaker. (Use a sensitive balance that can weigh to 3 decimal places.)
Allow the trichloromethane to evaporate in the sun (or use an electric heater to evaporate the trichloromethane in a fume chamber).
Fine white or yellow needle-like crystals will be observed. Weigh the beaker again.
The difference gives the amount of caffeine in 5g of tea leaves.
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