Grade Level: 9th to 12th Type: Chemistry
In this science fair project caffeine will be extracted from gunpowder green tea using dichloromethane and anhydrous sodium sulphate. The extracted caffeine will be validated by analysis with tannic acid. This investigation will illustrate the isolation of a naturally occurring product from a plant.
- What is dichloromethane and why is it used in this science fair project?
- What is tannic acid and why is it used in this science fair project?
- What is gunpowder green tea and why is it used in this science fair project?
- Does gunpowder green tea contain caffeine?
- Does the dichloromethane caffeine extraction procedure used in this project work?
- How much crude caffeine was separated from the gunpowder green tea leaves?
- Gunpowder green tea pellets (obtain at www.greenleaf-tea.com)
- Tannic acid
- Anhydrous sodium sulphate
- Distilled water
- Large ½ gallon pot
- Small metric kitchen food scale
- 25 ml separatory funnel
- Metric measuring cup
- Medicine dropper
- Test tubes
- Plastic teaspoon
- Two or three 125 ml beakers (or cups)
- Small plastic funnel
- Coffee filter
- Triple-beam balance
- This activity should be carried out under a fume-hood in a school chemistry laboratory or outdoors under a shad where there is ample ventilation.
- Place 300 gram of gunpowder green tea leaves into a large (500mL) pot.
- Fill the pot half-full with distilled water and stir.
- Boil everything for ten minutes on a hotplate.
- Allow mixture to cool after boiling.
- Pour the cooled tea solution into a 125 ml separatory funnel through a coffee filter to catch the tea leaves (be sure the funnel’s stopcock is closed).
- Add in 20 mL of dichloromethane.
- Stopper the separatory funnel.
- Keeping fingers on the stopper carefully shake the separatory funnel. Do not shake the separatory funnel too hard, or an emulsion will form, but swirl or rock the separatory funnel to mix the contents thoroughly.
- Vent the separatory funnel periodically with the spigot open to relieve gas pressure as shown in the illustration above.
- When the contents have been sufficiently shaken, stop.
- When two layers separate out, remove the stopper.
- Drain the bottom layer into a beaker or cup as shown in the illustration to the left.
- Dry the combined dichloromethane solutions and any emulsion layer by adding 1 teaspoon of anhydrous sodium sulphate.
- Carefully filter the dichloromethane solution into another beaker (cup).
- Either allow the dichloromethane to evaporate on its own or place the beaker in a hot water bath.
- When all the dichloromethane solvent has evaporated a residue of greenish-white crystalline caffeine will have been produced.
- To verify that caffeine has been extracted from the tea dissolve 1 gram of tannic acid in 1ml of alcohol, and dilute with distilled water to 10 ml. Prepare this solution fresh.
- Dissolve some of the crystalline caffeine residue in 2 ml of distilled water.
- Using a medicine dropper add tannic acid drop-wise to the crude caffeine. A white precipitate should form. Stop adding the tannic acid! If an excess amount of tannic acid is added, the precipitate will dissolve and disappear!
- Small amounts of the chemical compounds used in this project may be flushed down the sink using plenty of water unless local sanitary rules prohibit this.
- As an extension science fair project, after all the dichloromethane has been evaporated, the collected caffeine residue can be weighed on a balance and the data recorded. The same extraction procedure is followed but this time a decaffeinated tea is used and/or other tea types such as white, oolong, and black.
Terms/Concepts: gunpowder green tea, precipitate, tea infusion, caffeine, dichloromethane, emulsion, separatory funnel; What is caffeine?
References: Modern Projects and Experiments in Organic Chemistry, Jerry R. Mohrig, Christina Noring Hammond, and Paul F. Schatz, pp. 4-10 (W. H. Freeman and Company; 2nd edition 2002).