WB JEE Medical WB JEE Medical Solved Paper-2010

  • question_answer
    At identical temperature and pressure, the rate of diffusion of hydrogen gas is \[3\sqrt{3}\] times that of a hydrocarbon having molecular formula \[{{C}_{n}}{{H}_{2n-2}}.\]What is the value of n?

    A)  1                                            

    B)  4

    C)  3                                            

    D)  8

    Correct Answer: B

    Solution :

                     \[\frac{{{r}_{{{H}_{2}}}}}{{{r}_{{{C}_{n}}}}_{{{H}_{2n-2}}}}=\sqrt{\frac{{{M}_{{{C}_{n}}{{H}_{2n-2}}}}}{{{M}_{{{H}_{2}}}}}}\] \[=\sqrt{\frac{{{M}_{{{C}_{n}}{{H}_{2n-2}}}}}{2}}\]                 \[\because \]     \[\sqrt{\frac{{{M}_{{{C}_{n}}{{H}_{2n}}-2}}}{2}}=3\sqrt{3}=\sqrt{27}\]                 \[\Rightarrow \]               \[{{M}_{{{C}_{n}}{{H}_{2n-2}}}}=27\times 2=54\] Hence, \[12n+(2n-2)\times 1=54\] \[\Rightarrow \]                               \[14n=56\Rightarrow n=4\] Thus, hydrocarbon is \[{{C}_{4}}{{H}_{6}}.\]


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