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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