Isolation of Caffeine from a Tea Bag.edited (2)
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Isolation of Caffeine from a Tea Bag
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Isolation of Caffeine from a Tea Bag
Introduction
Tea is a widely used beverage with caffeine. Caffeine (C
8
H
10
N
4
O
2
) is a white,
odorless, and slightly bitter crystalline solid that can be extracted from tea using basic organic
chemistry techniques. The process involves boiling, extraction, separation, drying, and
evaporation.
Purpose
The purpose of this experiment is to isolate caffeine from the tea bag. Tea contains
other natural substances which might affect the extraction of caffeine. For instance, tea leaves
are primarily made up of cellulose. For the experiment to be effective, tea solution must be
prepared from the tea bag.
Materials
The experiment requires the following materials:
Tea bag (2.22g)
Watch glass
Glass beaker
Water
Pasteur Pipette
Methylene chloride
Anhydrous sodium sulfate
Spatula
Test tubes
Procedure
3
Preparing tea solution
Measure 20ml into a glass beaker and heat to boiling while covering it with the watch
glass. Place the tea bag into the hot water until it is completely covered.
Continue boiling for 15 more minutes while pushing the tea bag to ensure proper
contact with water. Use a Pasteur pipet to add more water.
Transfer equal amounts of the concentrated tea solution to 2 different centrifuge tubes
using a Pasteur pipet.
Ensure all the liquid is squeezed out of the tea bag. Note not to break the bag.
Extraction of the caffeine
Shake the mixture in the two centrifuge tubes for 5 seconds and add 3m2 CH
2
Cl
2
. A
clear layer forms at the bottom of the tubes.
Release the pressure from the tubes by venting. After shaking gently, the clear layer at
the bottom disappears. Shake the mixture for 30 seconds more while venting.
Centrifuge the mixture for 1 minute, separating the layers and breaking the emulsion.
Let the solution sit for 1 minute, and a layer begins to form. There is a green layer
between the clear methylene chloride layer and the top aqueous layer.
Use a Pasteur pipet to remove the lower organic layer and transfer it to a test tube.
Add 3ml of methylene chloride into the aqueous layer that remains in the centrifuge
tube.
Use a pipet to transfer the clear liquid into a new test tube
Add enough sodium sulfate to the clear solution.
Allow the mixture to sit for 15 minutes after stirring with a spatula.
Evaporation
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Transfer the clear liquid into a 50ml Erlenmeyer flask using a Pasteur pipet. Place the
flask in the hot water bath and let it evaporate.
After evaporation, crude caffeine coats the bottom of the flask. Avoid heating the flask
after the solvent evaporates.
Weigh the flask and note the weight of the crude caffeine.
Calculate the % recovery of caffeine from tea based on the initial weight of the tea
bag.
Sublimation of Caffeine
Sublimation can be used to purify caffeine
Rinse the caffeine completely from the flask using a few drops of methylene chloride.
Transfer the liquid to the sublimation apparatus.
Ensure the apparatus is air-tight by wrapping a foil around it
Heat the flask and let the mixture sublime for a few minutes
Put ice-cold water in the inner tube of the apparatus
The mixture begins to sublime after heating for 5-6 minutes
Stop heating when the sublimation is completed.
Remove the cold water and the ice from the inner tube, allowing the apparatus to cool.
Weigh the watch glass, then weigh the white powder together with the watch glass
Calculate the % recovery of caffeine after the sublimation
Compare the value to the % recovery determined after evaporation
Observations
After mixing tea solution with 3cm
2
of methylene chloride in the tube, there were two
layers observed, with a clear layers remaining at the bottom. The layers observed disappear
when the tubes are shaken. There was a little bump after the pressure inside the flask was
5
released. Allowing the solution to settle for 1 minute causes two layers to form. An aqueous
layer is formed at the top and a clear methylene chloride layer at the bottom. On the same
note, a green-brown layers forms between the two layers. The extracted caffeine is dark
yellow brown liquid.
Results
Caffeine collapses at 217.2
0
C but fully melts at 226.8
0
C. A collapsed caffeine is a
yellow light-brown powder, and the color changes to a dark-yellow liquid when fully melted.
After conducting the solid-liquid extraction and liquid-liquid extraction, the weight of the
resulting greenish-white caffeine crystals recorded was 0.02g. The mass of the organic extract
was 1.0g, while the original amount was 1.1g. The theoretical mass of caffeine after
sublimation was 0.11g. From the figures, it is possible to calculate the % recovery of
extraction and sublimation.
% Recovery of Extraction = mass of organic extract
x 100% = 1.0 g
x
100% = 91%
Original amount
1.1 g
% Recovery of Sublimation = mass of pure caffeine
x 100% = 0.02
g x 100% =18.2%
Theoretical mass of 0.11 g
Discussion
As expected from any experimental setup, the % yield of caffeine was not 100% after
extraction. Although the extraction of caffeine from the tea bag was successful, there was a
low percentage yield (18.2%).
Caffeine has basic properties from the lone pair of electrons in the nitrogen bonds
(Chin et al., 2008). In caffeine, nitrogen controls the solubility and melting point. The reason
for boiling tea with water is because it dissolves caffeine. Also, water played a role in
separating organic from inorganic compounds. The presence of other natural substances, such
6
as cellulose in tea, affects the extraction of caffeine. Cellulose is a polymer with an immense
amount of Hydrogen bonds, making water solution less polar (Chin et al., 2008). In this
instance, solubility will decrease due to the presence of Hydrogen bonds.
Methylene chloride was used because it is an effective solvent for dissolving caffeine
(Chin et al., 2008). Since Methylene chloride has a polarity, the presence of caffeine in the
solution lowers the solubility. Therefore solubility will decrease due to electrons being out of
hydrogen bonds. The sublimation process was used because it is a way of purifying caffeine
from water without melting it. Since sublimation does not have any external heat source, no
solvents are lost, unlike evaporation.
The sublimation apparatus was essential to this experiment since it allowed the heated
solvent to be cooled without the liquid evaporating (Chin et al., 2008). Without this, the mass
of the resulting caffeine would have been significantly lower than it was. After conducting the
extraction and sublimation, we obtained a yield of 0.11g caffeine from a 2.22 g tea bag using
water and Methylene chloride as solvents, which is a tiny percentage (18%) compared with
the initial mass (1g).
There are, however, many ways in which the extract could have been kept for longer
before measuring the impurity content. In a similar experiment, methylene chloride was
added to the tea bag after boiling. The extraction could have been carried out in this manner
by using an azeotropic mixture (a solvent that does not change the boiling point of the other
solvent).
Conclusion
The experiment successfully isolated caffeine from tea in four stages, i.e., preparation
of tea solution, extraction of caffeine, evaporation, and finally, sublimation. The results were
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compared, and the sublimation of caffeine was shown to be successful. Evaporation and
distillation have been used in the past, but nowadays, water is more frequently used for
extraction. Despite sublimation being a good method of purifying pure substances, it may not
be suitable for every substance as many factors are outside our control during this process.
8
References
Chin, J. M., Merves, M. L., Goldberger, B. A., Sampson-Cone, A., & Cone, E. J. (2008).
Caffeine content of brewed teas.
Journal of analytical toxicology
,
32
(8), 702–704.
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