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NEET AIPMT SOLVED PAPER MAINS 2012

  • question_answer
    Vapour pressure of chloroform \[(CHC{{l}_{3}})\] and dichloromethane \[(C{{H}_{2}}C{{l}_{2}})\] at \[{{25}^{o}}C\] are 200 mmHg and 41.5 mmHg respectively. Vapour pressure of the solution obtained by mixing 25.5 g of \[CHC{{l}_{3}}\] and 40 g of\[C{{H}_{2}}C{{l}_{2}}\]at the same temperature will be (Molecular mass of \[CHC{{l}_{3}}=119.5\,u\]and molecular mass of

    A)  173.9 mmHg    

    B)  615.0 mmHg

    C)  347.9 mmHg    

    D)  28.5 mmHg

    E) None of the above

    Correct Answer: E

    Solution :

    Number of moles of \[CHC{{l}_{3}},\]                                 \[{{n}_{A}}=\frac{w}{M}\]                                 \[=\frac{25.5}{119.5}\]                                 \[=0.213\]                 Number of moles of \[C{{H}_{2}}C{{l}_{2}},\]                                 \[{{n}_{B}}=\frac{40}{85}=0.47\]                 Mole fraction of \[CHC{{l}_{3}}\]                                 \[{{\chi }_{A}}=\frac{{{n}_{A}}}{{{n}_{A}}+{{n}_{B}}}\]                                 \[=\frac{0.213}{0.683}=0.31\]                 Mole fraction of \[C{{H}_{2}}C{{l}_{2}},\]                                 \[{{\chi }_{B}}=1-{{\chi }_{A}}\]                                 \[=1-0.31=0.69\]                 \[\because \] \[{{p}_{total}}={{p}_{A}}{{\chi }_{A}}+{{p}_{B}}{{\chi }_{B}}\]                                 \[=200\times 0.31+41.5\times 0.69\]                                 \[=62+28.63\]                                 \[=90.63mm\,Hg\]


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