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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

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