BCECE Engineering BCECE Engineering Solved Paper-2008

  • question_answer
    In a compound C, H and N are present in 9 : 1 : 3.5 by weight. If molecular weight of the compound is 108, then the molecular formula of the compound is

    A) \[{{C}_{2}}{{H}_{6}}{{N}_{2}}\]  

    B)        \[{{C}_{3}}{{H}_{4}}N\] 

    C)        \[{{C}_{6}}{{H}_{8}}{{N}_{2}}\]  

    D)        \[{{C}_{9}}{{H}_{12}}{{N}_{3}}\]

    Correct Answer: C

    Solution :

    \[\begin{align}   & \text{C}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\text{H}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\text{N} \\  & 9\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,1\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,3.5 \\  & 9/12=0.75\,\,\,\,\,\,\,\,\,\,1/1=1\,\,\,\,\,\,\,\,\,\,\,\,\,\,3.5/14=0.25 \\  & \frac{0.75}{0.75}=3\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\frac{1}{0.25}=4\,\,\,\,\,\,\,\,\frac{0.25}{0.25}=1 \\ \end{align}\] So, empirical formula \[={{C}_{3}}{{H}_{4}}N\]                                 \[n=\frac{108}{54}=2\]                 Molecular formula \[={{({{C}_{3}}{{H}_{4}}N)}_{2}}={{C}_{6}}{{H}_{8}}N{{ & }_{2}}\]


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