JEE Main & Advanced Chemistry Solutions / विलयन Question Bank Mock Test - Solutions

  • question_answer
    An ideal mixture of liquids A and B with 2 moles of A and 2 moles of B has a total vapour pressure of 1 atm at a certain temperature. Another mixture with 1 mole of A and 3 moles of B has a vapour pressure greater than 1 atm. But if 4 moles of C are added to the second mixture, the vapour pressure comes down to 1 atm. Vapour pressure of C, \[P_{c}^{0}\]=0.8 atm. Calculate the vapour pressures of pure A and pure B

    A) \[P_{A}^{o}\]=1.4 atm, \[P_{B}^{o}\]=0.7 atm

    B) \[P_{A}^{o}\]=1.2atm, \[P_{B}^{o}\]=0.6atm

    C) \[P_{A}^{o}\]=1.4atm, \[P_{B}^{o}\]=0.6atm

    D) \[P_{A}^{o}\]= 0.6 atm, \[P_{B}^{o}\]= 1.4 atm

    Correct Answer: D

    Solution :

    [d] \[{{P}_{T}}\](2 moles of A and 2 moles of B) is
    \[\frac{{{P}_{A}}^{o}}{2}+\frac{{{P}_{B}}^{o}}{2}=1atm\Rightarrow {{P}_{A}}^{o}+{{P}_{B}}^{o}=2atm\]
    \[P{{'}_{T}}\](1 mole of A and 3 moles of B)
    \[\frac{{{P}_{A}}^{o}}{4}+\frac{3{{P}_{B}}^{o}}{8}>1atm\Rightarrow {{P}_{A}}^{o}+3{{P}_{B}}^{o}>4atm\]
    \[P'{{'}_{T}}\](1 mole of A, 3 moles of B and 4 moles of C)
    And \[\frac{{{P}_{A}}^{o}}{8}+\frac{3{{P}_{B}}^{o}}{8}+\frac{4{{P}_{C}}^{o}}{8}=1atm\]
    \[\Rightarrow {{P}_{A}}^{o}+3{{P}_{B}}^{o}+4{{P}_{C}}^{o}=8atm\]
    So \[\Rightarrow {{P}_{A}}^{o}+3{{P}_{B}}^{o}=(8-4\times 0.8)atm\]
    \[=4.8atm\,\,({{P}_{C}}^{o}=0.8atm)\]
    Hence \[{{P}_{B}}^{o}=1.4atm\]
    \[{{P}_{A}}^{0}=0.6atm\]
     


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