My friends and I did it together, we also looked over it with a science teacher with a degree in chemistry and she said it was worthy of a distinction. PS: Don't copy word for word ;)
EXTRACTION OF CAFFEINE FROM TEA LEAVES
In this experiment we were not provided tea leave so we used tea bags instead.
To extract caffeine, we placed 6 tea bags in 500 ml beaker containing 250 cm3 of
distilled water and 5 g of sodium carbonate and stirred the contents of the beaker.
Then we gently squeezed the tea bags to liberate the rest of the water. We poured
contents into boiled water then let it cool in a water bath. After the tea solution had
cooled to room temperature we filtered the solution using glass wool. Then we
transferred the filtrate into a separating funnel for extraction 4 times using 10 cm3 of
dichloromethane. When extracting, we had to make sure there was no emulsion and
that we were swirling the 2 immiscible layers gently for about 4 minutes. While
swirling, we also made sure to open the lid of the separating funnel every 30
seconds to release the gas inside. After every extraction, we removed the organic
layer at the bottom of the funnel into a 250 cm3 beaker also leaving any emulsion
layer behind. We then added anhydrous sodium sulfate extracts to the beaker to
remove any water and water soluble salts that are retained in the dichloromethane
or any other impurities. Then we filtered the solution to remove the solid sulfate.
The dry solution we got after filtration was then transferred into a pre-weighed 250
ml beaker. We then placed the beaker containing the dry solution into a hot water
bath to evaporate the solution to dryness. When all the solvent is removed we
observed a residue of yellowish green. After the solution had evaporated to form
crude caffeine, we recrystallized the crude caffeine using methanol. After
recrystallization we got white crystalline caffeine. Then we measured the melting
point of the recrystallized crude caffeine using a sealed capillary tube.
OBSERVATION
After we added 5 g of sodium carbonate to 250 cm3 of distilled water containing tea
bags, the colour went from black to light brown. We let the tea solution cool down,
then we filtered it using glass wool. When we poured the tea solution into a
separating funnel and added dichloromethane, two layers formed (colourless
extract at the bottom and brown emulsion at the top). During the extraction
process, we noticed fizzing and every time the lid was removed there was a sound
of gas leaving the funnel. But at the end, there was no more fizzing because almost
all the gas had escaped. The colour of the precipitate was slightly green after
extraction, even after recrystallization the colour remained green.
TABLE OF RESULTS
Substance Melting point / ºC
Crude caffeine 237
Pure caffeine 237 - 238
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