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    TO DETECT THE CHLORINE PRESENT IN GIVEN ORGANIC COMPOUND

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    1. Experiment No. 8: TO DETECT THE CHLORINE PRESENT IN GIVEN ORGANIC COMPOUND
    2. OBJECTIVE:
    3. TO DETECT THE FOREIGN ELEMENT PRESENT IN GIVEN ORGANIC COMPOUND
    4. APPARATUS REQUIRED
    5. CHEMICALS REQUIRED
    6. THEORY
    7. PROCEDURE
    8. OBSERVATION TABLE
    9. Reactions involved
    10. RESULT
    11. CONCLUSION
    12. PRECAUTION

    Experiment No. 8: TO DETECT THE CHLORINE PRESENT IN GIVEN ORGANIC COMPOUND

    OBJECTIVE:

    TO DETECT THE FOREIGN ELEMENT PRESENT IN GIVEN ORGANIC COMPOUND

    APPARATUS REQUIRED

    1. Fusion tube
    2. Tong
    3. Burner
    4. Porcelain basin
    5. Beaker
    6. Test tube

    CHEMICALS REQUIRED

    • Sodium metal
    • Given organic compound
    • NaOH
    • FeSO4
    • FeCl3
    • HCl
    • Lead acetate
    • Sodium nitroprusside
    • AgNO3

    THEORY

    Organic compounds are covalent compounds and generally insoluble in water and carry out molecular reactions which are very slow. So, the given organic compound is fused with highly reactive metal such as sodium to give a water-soluble ionic compound which carries out ionic reactions which are fast. This test is known as the Lassaigne test. Nitrogen, sulphur and halogens are known as hetero elements or foreign elements.

    Foreign elements are those elements other than carbon, hydrogen and oxygen which form the basic constituent of organic compound. Foreign elements are covalently bonded with the carbon of organic compounds.

    1. If nitrogen is present, it forms sodium cyanide

    Na + C + N → NaCN → Na+ + CN–

    1. If sulphur is present, it forms sodium sulphide

    Na + S → Na2S → 2Na+ + S—

    1. If halogen is present, it forms sodium halide

    Na + Cl2 → 2NaCl → Na+ + Cl–

    Sometimes, when both nitrogen and sulphur are present in the same organic compound then sodium sulphocyanide is formed.

    Na + C + N + S → NaCNS → Na+ + CNS–

    PROCEDURE

    A freshly cut pea-shaped sodium metal was taken out from the kerosene oil and dried by pressing it between the folds of filter paper. The metal is placed in a fusion tube with a tong and was heated gently until the sodium melted to a shiny globule. Then a pinch of organic compound was added to it and heated strongly until the lower end of the tube became red hot. The hot tube was then plunged into the porcelain basin containing 10 ml of water. The particles were grinded with the pestle. The solution was foiled and filtered. The filtrate is called sodium extract solution (Lassaigne solution).

    OBSERVATION TABLE

    ExperimentObservationInference
    1. Detection of nitrogen:

    2 ml of sodium extract solution was
    taken in a clean and dry test tube and
    a few drops of NaOH solution was added.
    Then freshly prepared FeSO4 solution was
    added and boiled and cooled. Finally,
    FeCl3 solution was added and acidified with
    conc. HCl.    		Prussian blue colour was
    not obtained    		Absence of nitrogen
    2. Detection of sulphur:

    i. 2 ml of sodium extract solution was
    taken in a clean and dry test tube and
    a few drops of acetic acid solution were
    added followed by a few drops of lead acetate.    		Black ppt. was not obtainedAbsence of sulphur
    ii. 2 ml of sodium extract solution was
    taken in a clean and dry test tube and
    few drops of sodium nitroprusside solution
    was added.    		Violet color was not obtainedAbsence of sulphur
    3. Detection of nitrogen and sulphur together:

    2 ml of sodium extract solution was taken in
    a clean and dry test tube and a few drops
    of ferric chloride solution was added.
    Blood red color was not obtained
    Absence of nitrogen and
    sulphur together
    4. Detection of halogen:

    2 ml of sodium extract solution was
    taken in a clean and dry test tube and
    acidified with nitric acid and a few drops
    of AgNO3 solution was added to it.
    White ppt. was obtained that
    dissolve in nitric acid and
    reappears with nitric acid.
    Presence of halogen

    Reactions involved

    2Na + Cl_{2} \rightarrow NaCl + AgNO_{3}\\
NaCl + AgNO_{3} \rightarrow \underset{White\ ppt.}{AgCl} + NaNO_{3}\\
AgCl + NH_{4}OH \rightarrow \underset{Diamine\ silver\ chloride}{[Ag(NH_{3})_{2}]Cl}\\
 \left [Ag(NH_{3})_{2}Cl  \right ] + 2HNO_{3} \rightarrow AgCl + 2NH_{4}NO_{3}

    RESULT

    The given sample of organic compounds contained chlorine as a foreign element.

    CONCLUSION

    We can detect the foreign element present in a given organic compound by Lassaigne test.

    PRECAUTION

    1. A large amount of sodium metal was not taken.
    2. The contents of the basin were boiled only after the completion of unreacted sodium.
    3. If a dark colour was formed, the compound was not decomposed completely and the process was repeated.
    Check out Grade 12 Chemistry Notes

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