CONTENTS
1. Introduction
2. Aims of the Experiment & Requirement
3. Theory
4. Procedure
5. Observation
6. Result
TANNIC ACID
Tannins are polyphenolic biomolecules with carbohydrate backbones
that are found in a wide range of plants. Tannic acid is a specific tannin
that formally contains 10 galloyl(3,4,5-trihydroxyphenyl) units
surrounding a glucose centre. Commercial tannic acid however, consist
of molecule with 2-12 galloyl moieties.
Tannic acid contains no carboxyl groups, but is weakly acidic because of
the multiplicity of phenolic hydroxyls. The hydroxyls also cause it to be
extremely soluble in water. All regulatory authorities classify it as a
nonhazardous substance.
As the name implies, tannins are used in leather tanning. Other
commercial uses are in dyeing, ink manufacture, paper sizing, food and
wine processing, and production of gallic acid and pyrogallol.
Tannic acid has anti-bacterial, anti-enzymatic and astringent properties.
Tannic acid has constringing action upon mucous tissues such as tongue
and inside of mouth. The ingestion of tannic acid caused constipation
and can be used to treat diarrhoea (in the absence of fever or
inflammation). The anti-oxidant and antimutagenic properties of tannic
acid are beneficial.
Tannic acid is also used in many industrial applications. The best known
is the tanning of leather. Tannic acid is sometimes used to clear wines.
Tannic acids reacts with proteins in wine to form Insoluble complexes
which sediment or can be filtered.
Tannic Acid Facts
CAS Reg.No.
1401-55-4
Molar Mass
1701.2 g/mol
Empirical Formula
C76H52O46
Appearance
Light Yellow to Tan Solid
Boiling Point
218°C
Water Solubility
2850 g/L*
AIM OF THE EXPERIMENT:To compare the tannic acid content of various samples of
Tea.
REQUIREMENT:1. Beakers
2. Conical Flasks
3. Funnel
4. Heating Arrangements
5. Various Sample of Tea
6. Calcium Carbonate
7. Conc. HCL
THEORY:The tannic acid present in tea leaves is precipitated as
calcium tannate by treatment of agueous solution of tea
with calcium carbonate, calcium tannate is then
hydrolysed with Conc. HCL and recrystalized from water.
PROCEDURE:1. We had weighed 10 mg of tea each of given samples of tea.
2. We had taken 100ml of distilled water in 500 ml beaker and had
boiled it, then we had added the first sample of ten leaves to it
and had boiled for 10 minutes. We had cooled and filtered the
solution.
3. To filtrate we have added about 2 gm of solid calcium carbonate
and had boiled the contents. Tannic acid gets precipitated as
calcium tannate. We had separated the precipitate of calcium
tannate by filtration.
4. Calcium tannate obtained had been hydrolysed by warming with
4-5 ml of Conc. HCL, the tannic acid obtained had been
crystalised from water and weighed.
5. We had repeated the steps 2,3 and 4 with the other samples of
tea and recorded the observation.
OBSERVATIONS:SL.No
Samples of
Tea
Weight of
tea leaves
taken ‘x’ (in
gm)
Weight of
tannic acid
obtained
% of tannic
acid =y |
x*100
1
A
10
0.002
0.02
2
B
10
0.08
0.8
3
C
10
0.02
0.2
RESULTS:The tea samples B contains highest percentage of Tannic
Acid. Hence it gives better flavor than A & C.