CHEMISTRY PROJECT
EXPERIMENT
Aim :
.
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Requirements :
China dish:
Test-tube
funnel:
Filter
paper:
Common laboratory
reagents
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Theory :
•Brass is an
alloy of copper
and zinc. with
the following.
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Composition :
Cu = 60-90% and Zn. =
10-40%.
Thus Cu and Zn. form
the main constituents of
brass. Both these metals
dissolved in 50% of nitric
acid due to formation of
nitrates which are
soluble.
3 Cu + 8HNO3 (Dil)
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3 Cu (NO3)2 + 2NO +
4H2O
Or
Cu + 8H+ + 2NO3– 3
Cu+2 + 2NO + 4H2O
4Zn + 10HNO3 (Dil) 4 Zn
(NO2)2 + N2O + 5H2O
4Zn + 2NO3– + 10H+ 4
Zn+2 + N2O + 5H2O
The solution is boiled to
expel the oxides of
nitrogen and the resulting
solution is tested for Cu2+
and Zn+2 ions
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Procedure :
1. Place a small piece of brass in a
china dish and heat this with
minimum quantity of 50% HNO3
so as to dissolve the piece
completely.
2. Continue heating the solution
till a dry solid residue is obtained.
3. Dissolve the solid residue in dil.
HCl and filter. Add distilled water
to the filtrate.
4. Pass H2S gas through the
filtrate. A black precipitate of
copper sulphide is obtained.
Separate the black ppt. and keep
the filtrate for the test of Zn+2
ions Dissolve black ppt.
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by heating them with 50%
HNO3. To this solution add
ammonium hydroxide solution.
Appearance of deep blue
colouration in the solution shows
the presence of copper ions in the
solution.
5. To test Zn+2 ions, boil the
filtrate to remove H2S gas, then
add solid NH4Cl to this and heat
to dissolve NH4Cl. Add excess of
NH4OH so that a solution is
ammonia cal. Now pass H2S gas
through this ammonia cal
solution. Dirty white or grey
precipitation indicates zinc.
Separate the precipitates and
dissolve it in minimum amount
of dil. HCl. Boil to expel H2S gas
and add potassium Ferro cyanide
solution, white or bluish white
ppt. confirm Zn+2 ions in the
solution.
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Result :
The given
sample of brass
contains copper
and zinc metals
as the main
constituents.