KVPY Sample Paper KVPY Stream-SX Model Paper-15

  • question_answer
    One mole of an organic compound A with the formula \[{{C}_{3}}{{H}_{8}}O\] reacts completely with two moles of \[HI\] to from X and Y. When Y is boiled with aqueous alkali it forms Z. Z answers the iodoform test. The compound A is

    A) propan-2-ol

    B) propan-1-ol

    C) ethoxyethane    

    D) methoxyethane

    Correct Answer: D

    Solution :

    Molecular formula
    \[{{C}_{3}}{{H}_{S}}O({{C}_{n}}{{H}_{2n+2}}O)\] suggests that the organic compound is either alcohol or ether. Since, the compound on reaction with HI gives two different compounds, it must be an unsymmetrical ether and its formula must be \[C{{H}_{3}}O{{C}_{2}}{{H}_{5}}\] (methoxyethane).
    The reactions are as follows:
    \[\underset{\begin{smallmatrix}  \text{Methoxyethane} \\  (A) \end{smallmatrix}}{\mathop{C{{H}_{3}}O{{C}_{2}}{{H}_{5}}}}\,+2HI\xrightarrow{{}}\underset{X}{\mathop{C{{H}_{3}}I}}\,+\underset{Y}{\mathop{{{C}_{2}}{{H}_{6}}I}}\,+{{H}_{2}}O\]
    \[\underset{Y}{\mathop{{{C}_{2}}{{H}_{5}}I}}\,+\underset{\text{Aqueous}}{\mathop{2NaOH}}\,\xrightarrow{{}}\underset{Z}{\mathop{{{C}_{2}}{{H}_{5}}OH}}\,+NaI\]
    \[\underset{(Z)}{\mathop{{{C}_{2}}{{H}_{5}}OH}}\,+\underset{\text{Aqueous}}{\mathop{6NaOH}}\,+3{{I}_{2}}\xrightarrow{{}}\underset{\text{Iodoform}}{\mathop{CH{{I}_{3}}}}\,\]
    \[+\overset{-\,+}{\mathop{HCOONa}}\,+{{H}_{2}}O+5NaI\]
    Thus, the compound 'A' is methoxyethane.


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