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INVESTIGATORY
PROJECT
2. INTRODUCTION
3. APPARATUS REQUIRED
4. THEORY
5. PROCEDURE
6. OBSERVATIONS
7. CONCLUSION
8. PRECAUTIONS
9. BIBLIOGRAPHY
AIM
To prepare alum from
aluminium foil
1
INTRODUCTION
Aluminium because of its low density, high tensile
strength and resistance to corrosion is widely used
for the manufacture of aeroplanes, automobiles lawn
furniture as well as for aluminium cans. Being good
conductor of electricity it is used for transmission of
electricity. Aluminium is also used for making
utensils. The recycling of aluminium cans and other
aluminium products is a very positive contribution to
saving our natural resources. Most of the recycled
metal products are used in the production of various
aluminium compounds. The most common of which
are the alums. Alums are double sulphates having
general formula
X2SO4.M2(SO4)3.24H2O
X = Monovalent cation; M = Trivalent cation;
2
Some important alum and their names are given
below:
K2SO4.Al2(SO4)3.24H2O -Potash Alum
Na2SO4.Al2(SO4)3.24H2O-Soda Alum
K2SO4.Cr2(SO4)3.24H2O -Chrome Alum
(NH)2SO4.Fe2(SO4)3.24H2O - Ferric Alum
Potash alum is used in papermaking, in fire
extinguishers, in food stuffs and in purification of
water soda alum used in baking powders and chrome
alum is used in tanning leather and water proofing
fabrics.
In addition to these primary uses, alum is also used
as
1. An astringent a substance or preparation that
draws together or constricts body tissues and is
effective in stopping the flow of blood or other
secretions. Alum has also been used by conventional
hairdressers for treating shaving cuts.
3
2. A mordantsubstances used in dyeing to fix certain
dyes on cloth. Either the mordant (if it is colloidal)
or a colloid produced by 7 the mordant adheres to
the fiber, attracting and fixing the colloidal mordant
dye. The insoluble, colored precipitate that is formed
is called a lake. Alum is a basic mordant used for
fixing acid dyes.
3. For the removal of phosphate from natural and
waste watersthe aluminium ions of alum combine
with the orthophosphate around pH 6 to form the
solid aluminum hydroxyphosphate which is
precipitated.
4. For fireproofing fabrics:-The major uses of alums
are based on two important properties, namely
precipitation of Al(OH)3 and those related to the
acidity created by the production of hydrogen ions.
Al(H2O)6 +3→ Al(OH)3↓ + 3H2O + 3H+.The H+ ions
generated are used for reacting with sodium
bicarbonate to release CO2. This property is made
use of in baking powder and CO2 fire extinguishers.
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APPARATUS REQUIRED
250 ml flask
Funnel
Beaker
Water Bath
Ethanol
Aluminium foil
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Potassium hydroxide solution (KOH)
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THEORY
Aluminum metal is treated with hot aqueous KOH
solution.
Aluminium dissolves as potassium aluminate, KAl
(OH) 4, salt.
2Al(s) + 2KOH(aq) + 6H2O(l) 2KAl(OH)4(aq) + 3H2
Potassium aluminate solution on treatment with dil.
Sulphuric acid first gives precipitate Al (OH) 3,
which dissolves on addition of small excess of
H2SO4 and heating.
2KOH(aq) + H2SO4(aq) 2Al(OH)3(s) + K2SO4(aq)+2H2O(l)
2Al(OH)3 (s)+ 3H2SO4(aq) Al2(SO4)3(aq) +6H2O(l)
The resulting solution is concentrated to near
saturation and cooled.
On cooling crystals of potash alum crystallize out.
K2SO4 (aq) + Al2 (SO4)3(aq) +24H2O (l) K2SO4.Al2
(SO4)3. 4H2O(s)
REACTIONS
2Al(s) +2KOH (aq) + 6H2O (l) 2KAl (OH) 4 (aq) + 3H2
K2SO4 (aq) + Al2(SO4)3(aq)+ 24H2O (l) K2SO4.Al2(SO4)3.
24H2O(s)
2Al(OH)3(s)+ 3 H2SO4(aq) Al2(SO4)3(aq) +6H2O(l)
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2KOH(aq) + H2SO4(aq) 2Al(OH)3(s) + K2SO4(aq) +
2H2O(l)
K2SO4 (aq) + Al2 (SO4)3(aq) +24H2O (l) K2SO4.Al2.(SO4)3.24H2O(s)
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PROCEDURE
Clean a small piece of scrap aluminium with
steel wool and cut
it into very small pieces. Aluminium foil may be
taken instead
of scrap aluminium.
Put the small pieces of scrap aluminium or
aluminium foil
(about 1.00g) into a conical flask and add about
50 ml of 4 M
KOH solution to dissolve the aluminium.
The flask may be heated gently in order to
facilitate
dissolution. Since during this step hydrogen gas
is evolved this
step must be done in a well-ventilated area.
Continue heating until all of the aluminium
reacts.
Filter the solution to remove any insoluble
impurities and
reduce the volume to about 25 ml by heating.
Allow the filtrate to cool. Now add slowly 6 M
H2SO4 until
insoluble Al (OH)3 just forms in the solution.
Procedure
Gently heat the mixture until the Al(OH)3
precipitate dissolves.
Cool the resulting solution in an ice-bath for
about 30 minutes
whereby alum crystals should separate out. For
better results
the solution may be left overnight for
crystallization to
continue.
In case crystals do not form the solution may
be further
concentrated and cooled again.
In case crystals do not form the solution may
be further
concentrated and cooled again.
Filter the crystals from the solution using
vacuum pump, wash
the crystals with 50/50 ethanol-water mixture.
Continue applying the vacuum until the
crystals appear dry.
Determine the mass of alum crystals.
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OBSERVATIONS
Mass of aluminium metal =1.00g
Mass of potash alum =4.20g
Percent yield =420%
From 1g of aluminium we can extract approximately 5g of
potash alum profitably.
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CONCLUSION
Alum of 420% yield was prepared from
aluminium foil.
PRECAUTIONS
Handle the glass wares safely.
Allow the time required to set.
Spray only required amount of water.
BIBLIOGRAPHY
HE LP FROM INTERNET
www.wikipedia.org
www. icbse.com
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PROCEDURE
Clean a small piece of scrap aluminium with
steel wool and cut
it into very small pieces. Aluminium foil may be
taken instead
of scrap aluminium.
Put the small pieces of scrap aluminium or
aluminium foil
(about 1.00g) into a conical flask and add about
50 ml of 4 M
KOH solution to dissolve the aluminium.
The flask may be heated gently in order to
facilitate
dissolution. Since during this step hydrogen gas
is evolved this
step must be done in a well-ventilated area.
13