The after separating the solvents, residual water will remain

The solution
of these dissolved compounds is referred to as an extract. The process is
extremely important in a wide range of technical applications, for instance,
biotechnology, the pharmaceutical and food industries as well as environmental
protection. Extraction is a separating process which has the advantage of low
energy consumption, high efficiency, high selectivity and less expensive
alternative compared with competing separating methods such as distillation,
evaporation and membrane technology.

This
experiment will be conducted to extract caffeine sample from tea. Tea itself is
a beverage that is commonly used by many people since 2,000 years ago in China
and infusing the young leaves basically produces it and leaf buds of the tea
plant, in the boiling water. In terms of this chemical composition, the
chemical substances in tea can be divided into two major groups: water and dry
matter. In this case of this experiment, we will focus on the organic compound
caffeine.

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Caffeine is
a chemical name, 1,3,7 – trimethylxanthine, belongs to a wide class of
compounds known as alkaloids that is found in over 60 plant species. Caffeine
is found in coffee (100 mg/cup), tea (30-75 mg/cup), chocolate (6-35 mg/oz),
and cola (46 mg/12 oz). The caffeine itself is belong to a family of naturally
occurring compounds known as xanthine’s which is considered as the oldest known
stimulants. The biological function of alkaloids in plants is still unknown,
but the small amount of it in animal organism and humans’ shows remarkable
physiological effect. Additionally, this organic compound is considered as the
most powerful xanthine in its ability to increase alertness, put off sleep, to
increase ones capacity for thinking, relaxes the blood vessels and increases
urination. Due to its structure, caffeine is both soluble in polar and
non-polar solvent. The solubility of caffeine in water is 22mg/ml at 25°C,
180mg/ml at 80°C, and 670mg/ml at 100°C. In this experiment, the organic solvent
dichloromethane (CH2Cl2) is used to extract caffeine from aqueous extract of
tea powder because caffeine is more soluble in dichloromethane (140mg/ml) than
it is in water (22mg/ml). The dichloromethane and caffeine mixture can then be
separated on the basis of the different densities of dichloromethane and water
because dichloromethane is much denser than water and insoluble in it. Residual
water is separated from dichloromethane by drain out the dichloromethane
through separating funnel, thus dichloromethane passed through the funnel while
polar solvents such as water is still remains in the funnel. But since, water
and dichloromethane is slightly soluble in each other, so after separating the
solvents, residual water will remain the organic layer.

However in
the tea leaves, caffeine does not exist as the only organic compound. Instead,
the tea leaves are mainly consisting of cellulose, pigments, chlorophylls, and
tannins. Tannin, also called Tannic Acid, is any of a group of pale-yellow to
light-brown amorphous substances in the form of powder, flakes, or a spongy
mass, widely distributed in plants and used chiefly in tanning leather, dyeing
fabric, making ink, and in various medical applications. Tannin solutions are
acid and have an astringent taste. This organic compound is responsible for the
astringency, color, and some of the flavor in tea. The presence of these other
compounds finally may lead to the impurity of the caffeine after it has been
extracted from the tea sample which may cause alteration in the method used in
extracting the tea sample, which will be shown later in the report.

There is a
huge myth surrounding tea and caffeine, and the amounts different colors
produce.  Often it is believe that Black
teas have the highest levels while white teas are the lowest.  This is largely false, as the strength in tea
has largely to do with brewing, kind of leaves or buds, and how it was
grown.  Furthermore, it can also depend
on the brand of the tea, as for example, green tea usually contains 35mg of tea
per cup, but it can vary from 30 to 50 mg depending on the stated factors.