NEET Chemistry NEET PYQ-Solutions

  • question_answer
    Which of the following statement about the composition of the vapour over an ideal a 1 : 1 molar mixture of benzene and toluene is correct?  Assume that the temperature is constant at \[25{{\,}^{o}}C.\]  (Given : Vapour Pressure Data at \[{{25}^{o}}C,\] benzene = 12.8 kPa, Toluene = 3.85 kPa) [NEET - 2016]

    A) The vapour will contain a higher percentage of benzene

    B) The vapour will contain a higher percentage of toluene

    C) The vapour will contain equal amounts of benezene and toluene

    D) Not enough information is given to make a predication

    Correct Answer: A

    Solution :

    [a] A\[\to \] benzene, \[\to \] toluene
    1 : 1 molar mixture of A and B
    \[\therefore \]      \[{{x}_{A}}=\frac{1}{2}\]and \[{{x}_{B}}=\frac{1}{2}\]
    \[P{{}_{s}}=P_{A}^{0}{{X}_{A}}+P_{B}^{0}{{X}_{B}}\]
    \[{{P}_{s}}=12.8\times \frac{1}{2}+3.85\times \frac{1}{2\,}=8.325\,\text{kPa}\]
    \[{{Y}_{A}}=\frac{P_{A}^{0}{{X}_{A}}}{{{P}_{s}}}=\frac{12.8\times \frac{1}{2}}{8.325}=0.768\]
    \[\therefore \] \[{{Y}_{B}}=1-{{Y}_{A}}=1-0.768=0.232\]
    so, the vapour will contain higher percentage of benzene.


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