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KVPY Sample Paper KVPY Stream-SX Model Paper-2

  • question_answer
    An organic compound whose empirical and molecular formula are same, contains \[~20%\]% carbon, \[6.7%\]% hydrogen, \[46.7%\]% nitrogen and the rest oxygen. On heating it yields ammonia, leaving a solid residue. The solid residue. a violet colour with dilute solution of alkaline  copper sulphate. The organic compound is

    A) \[N{{H}_{2}}COON{{H}_{4}}\]          

    B) \[HCOON{{H}_{4}}\]

    C) \[N{{H}_{2}}NHCHO\]

    D) \[N{{H}_{2}}CON{{H}_{2}}\]

    Correct Answer: D

    Solution :

    Element % Atomic mass Relative no. of atoms Simplest ratio
    C 20 12 1.66 1
    H 6.7 1 6.7 4
    N 46.7 14 3.33 2
    O 26.6 16 1.66 1
    Empirical formula = Molecular formula =\[C{{H}_{4}}{{N}_{2}}O\]
    or \[N{{H}_{2}}CON{{H}_{2}}\]\[{{H}_{2}}NCON{{H}_{2}}+{{H}_{2}}NCON{{H}_{2}}\xrightarrow{\Delta }\]\[{{H}_{2}}{{\underset{biuret}{\mathop{NCONHCONH}}\,}_{2}}+N{{H}_{3}}\]
    When an aqueous solution of residue is treated with dilute sodium hydroxide and a drop of copper sulphate, a violet colour is produced. This test is known as biuret test, is characteristic of compounds having the group -CONH.


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