AFMC AFMC Solved Paper-2008

  • question_answer
    The density of a gas is \[1.964\,\text{g}\,\text{d}{{\text{m}}^{-3}}\] at 273 K and 76 cm Hg. The gas is

    A)  \[\text{C}{{\text{H}}_{\text{4}}}\]                                         

    B)  \[{{C}_{2}}{{H}_{6}}\]

    C)  \[C{{O}_{2}}\]                                  

    D)  \[Xe\]

    Correct Answer: C

    Solution :

                     We know that \[pV=nRT\] or            \[pV=\frac{w}{M}RT\] or            \[M=\frac{w}{V}\frac{RT}{p}\] or            \[M=d\frac{RT}{p}\] \[d=1.964\,g/d{{m}^{3}}=1.964\times {{10}^{-3}}\,g/cc\] \[p=76\text{ }cm=1\text{ }atm\] \[R=0.0821\,\text{L}\,\,\text{atm}\,{{\text{K}}^{-1}}\text{mo}{{\text{l}}^{-1}}\] \[=82.1\,\text{cc atm}\,{{\text{K}}^{-1}}\,\text{mo}{{\text{l}}^{-1}}\] \[T=273\,K\] \[M=\frac{1.964\times {{10}^{-3}}\times 82.1\times 273}{1}=44\] The molecular weight of \[\text{C}{{\text{O}}_{\text{2}}}\] is 44. So, the gas is \[\text{C}{{\text{O}}_{\text{2}}}.\]


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