chemistry class 12 investigatory project topic : amount of caffeine present in tea leaves

5. Tea is a highly popular drink all over the world.A
cup of tea is often taken as a mind-freshner.This
can be primarily attributed to the presence of a
stimulant called CAFFEINE in the tea.Besides this
tea also contains various polyphenolic compounds
that act as flavourings agents. Relative contents of
these compoundsresult in different varieties avail-
able underdifferent brand names.
The quality of tea leaves also greatly influence of
the taste of the tea.
Tea is popular name of the tropical plant whose-
botanical name is Camellia thea. India is the larg-
est producer of good quality tea and it is mainly
grown in slope of hills of Assam, West Bengal and
Nilgiri Hills. A cup of Indian tea contains 80mg of
caffeine which is the indispensable content of tea.
INTRODUCTION
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6. PG:02
Caffeine is a nitrogenous organic compound of
alkaloid group. These groups of substances have
a marked physiological effect on the human
body when taken in considerable amount. It is
widely used as a stimulant of the central nervous
system and also has hypotonic and sleep induc-
ing effect. Pure caffeine has the general formula
C8 H10 N402. IUPAC name of this substance is
1, 3, 7-trimethyl xanthamine.It occurs as a white
powder that melts at around 238 C. It is fairly
soluble in hot water and on cooling the solution
gives crystals made up of caffeine monohydrate.
In this case thecompound is less soluble in or-
ganic solventsthan in hot water. It is odorless
but even a small amount have a very bitter taste.
Caffeine is the main flavoring agent in the tea
leaves.

7. PG:03
It is obtained from the decaffeination of tea
dust and also from coffee.It exerts a simula-
tive effect on the cerebral cortex but later has
a depressant and narcotic action. It is also
useful in cardiac dropsy. An abnormal sate
arising from caffeine is called caffeinism.
The main symptoms are nervousness, In-
somnia and Tachycardia. It is used in medi-
cines in the form of chlorides and nitrates.In
this project we will do a careful study of dif-
ferent brands of tea and will extract and care-
fully analyze their caffeine content. The result
would thus tell the exact content of caffeine
present in different samples analyzed.

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APPARATUS REQUIRED
1.Round bottom flask
2.Bunsen burner
3.Beakers

9. PG:05
Chemicals required
1.Lead nitrate
2.Lead oxide
3.Chloroform
4.Distilled water
5.Animal charcol
6.Dilute mineral acid

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Procedure
1.In a litre round bottom flask 40gm of first
sample was taken.
2.To this about 250ml of distilled water was
added and thecontents were refluxed for about
an hour.
3.The brown colour extracted is separated by
decantationfollowed by filtration when still
hot.
4.Lead acetate is dissolved into water in 250ml
beaker.
5.The solution is boiled and the lead oxide is
added slowly tothe boiling solution with con-
stant stirring.
6.It is filtered and again boiled.
7.The filterate thus obtained is added dropwise
to this extract tillno precipitation occurs.

11. 8.The filtrate is treated with animal charcoal to
decolouriseextract.
9.The clear solution is extracted with 100mg of
chloroform afterseparating by filtration.
10.The total solution is taken into distillation
flask to remove thesolvent by distillation.
11.The residue left in the flask is dissolved in
minimum amount of hot water and the dis-
solved contents are transferred to theboiling
tube.
12.The solution is kept for slow crystallization.
13. When the white crystalline solid comes out
of the solution it isfiltered, dried in desiccators
and weighed.
14.The above procedure is repeated for all sam-
ples of tea.
15.The observations are carefully recorded.
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12. Chemistry involved behind the
experiment
1.Caffeine being soluble in water goes into theso-
lution on refluxing.
2.Lead oxide when added to lead acetatesolution
helps lead to precipitate and comeout in the form
of insoluble lead sulphate as it is a basic oxide.
3.The activated charcoal adsorbs the colouredpig-
ments from the brown coloured solution.
4.Chloroform is used for extracting the caffeineas
it is a more soluble in CHCl3 than in coldwater.
5.On boiling caffeine being more volatileevapo-
rates leaving a white mass behind.
5.On adding more chloroform and bygradual
evaporation we get nice crystallinecaffeine.
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13. OBSERVATION
About 49gm of each sample was taken. The con-
tents of caffeine of the samples were noted and
their presence in terms of percentage was calcu-
lated.
Name of the Tea
variety
Caffeine contents Composition in per-
centage
Taste
Red label 0.029 0.0725% Mild and
soothing
Taj mahal 0.05 0.0125% Slightly strong
Tata tea 0.036 0.09% Strong
pleasant
Lipton tea 0.047 0.1175% Very strong
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14. Inference
FROM THE CAFFEINE CONTENT AND
THE TASTE OF THE TEA AS DESCRIBED
ABOVE SHOWS THAT THE GREATER THE
AMOUNT OF CAFFEINE, THE BITTERNESS
AND STIMULATING EFFECT OF THE TEA.
Bibliography
1.Reference from Internet
2.Help of teacher
A.K.ROHITH
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