experiment 6 presentation
TRANSCRIPT
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Experiment 6
ELEMENTAL ANALYSIS
By: Catherina Barcel and
Rogelio Rivera
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INTRODUCTION
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Elemental Analysis
It is the process where a substance is
analyzed for its elemental composition
C,H,O,N,S,P,X
In the case of our experiment,
what we did was a qualitative
elemental analysis, that is, we
only want to know what elementsmake up the substance
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SODIUM FUSION
(Lassaignes test)
When an organic material is strongly heated with
sodium, it turns into an inorganic sodium salt
WHY SODIUM?
Because sodium is highlyreactive, has a low
melting point, and most of
its salts are soluble in
water.
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CAUTION!!!
Sodium is highly reactive in water, it
violently reacts with water
The reaction is highly exothermic
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OUR TEST SAMPLES
P-chloroaniline thioacetamide
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PROCEDURES
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Sodium fusion
A piece of Na was heated in a test tube
until no vapor was observed
P-chloroaniline was added
The test tube was heated to initiate thereaction. Then, the tube was removed and
heated again to redness
The tube was placed in water (it shattered,
its okay.)
Allow excess sodium to react. Then the
solution was boiled and filtered
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QUALITAIVE TESTS
Fusion solution + water in test tube
Add nitroprusside
Blue violet solution should be seen
Sulfur test
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Nitrogen Test
Add FeSO4 to fusion solution in test tube.
Add KF and boil
Add FeCl3 and add sufficient H2SO4 to
dissolve excess iron hydroxides and toacidify the solution ( to dissolve any free
alkali)
Blue solution should be seen
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Halogen Test
If the sample is positive for nitrogen or
sulfur, acidify the fusion solution with
HNO3 and boil
Add AgNO3
and look for precipitates.
Heavy curdy-type precipitate indicates the
presence of halogens. If sample is only
slightly turbid, test is negative.
AgCl(white precipitate) AgBr (pale yellow
precipitate) AgI (yellow precipitate)
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RESULTS
Test sample Sulfur Nitrogen Halogen
Cl Br I
P-chloroaniline - + + - -
Thioacetatamide + + - - -
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DISCUSSION
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Sodium fusion
It was developed by J.L. Lassaigne
It is used for detection of halogens,
sulfur, and nitrogen
In theory, when sodium is reacted withany halogens, sulfur, or nitrogen, they
will be converted to inorganic salts and
can therefore be detected by inorganic
analysis
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Sulfur Test
Sodium nitroprusside reacts with sodium
sulfide to form Na4[Fe(CN)5NOS] which
forms the deep blue-violet color
It can also be noted that sulfur has a
distinctly smelly odor.
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Nitrogen Test
Addition of Fe2+ from the FeSO4 and Fe3+
from the FeCl3 converts the CN- ions into
ferric ferrocyanide which gives the
prussian blue color
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Halogen Test
Beilstein test
By Fredrich Konrad Beilstein
A preheated (to remove any NaCl
present from the handling of the wire)copper wire is dipped into the fusion
solution and then burned. A blue green
flame indicates the presence of a
halogen. The color comes from the light
emitted from the excited states of thecopper halide.
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The AgCl test:
The reactions of the halogen ion with the silver ion
are as follows:
White precipitate
Pale yellow precipitate
Yellow precipitate
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BUT WAIT, THERES
MORE!
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Oxygen
There is no direct method for the detection
of oxygen (Vogel).
If the known chemical formula is still
insufficient to account for the mass of
the sample
Ignition
If it relights a glowing splint
Organic molecules produce blueflames when heated when they
contain oxygen
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For Phosphorus
Ammonium molybdate reagent
Add a large excess of that to the test
solution and it will produce a yellow
precipitate.
Phosphorous also smells like phosphine
(garlicky or rotting flesh smell) during sodium
fusion Note that arsenic also behaves like
phosphorus in this test so oxidize it first to be
sure!
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OTHER METHODS
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For Sulfur
Acidify the fusion solution
Add a few drops of lead acetate
A black precipitate will be apparent if the
solution contains sulfur
Black precipitate
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For Nitrogen
Mix p-nitrobenzaldehyde with in
methoxyethanol and o-nitrobenzaldehyde
in methoxyethanol and an aqueous
solution of sodium peroxide. Add a small
amount of the fusion solution and a deeppurple color tests positive for cyanide ions.
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How do we differentiate between
AgCl, AgBr and AgI?
Try the solubilities in ammonia.
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If you really, really want to make sure that the
precipitate is AgCl
If the silver chloride is filtered off,
washed with distilled water, and
then shaken with sodium arsenite
solution it is converted into yellowsilver arsenite (Vogel).
Silver iodide and silver bromide are
unaffected.
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If you really have doubts, there
may be multiple halogens
Reaction if iodine is present
Reaction if bromine is present
For chlorine, add excess glacial acetic acid
and slight excess of lead dioxide. Boil andrepeat silver nitrate test for halogens.
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END OF DISCUSSION.
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REFERENCES
Vogels Textbook of Macro and Semimicro
Qualitative Inorganic Analysis 5th ed, 1979
Vogels Textbook of Practical Organic
Chemistry 5th ed, 1989
www.wikipedia.org
Higher batches