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JEE Main & Advanced Chemistry Solutions / विलयन Question Bank Lowering of vapour pressure

  • question_answer
    If two substances \[A\] and \[B\] have \[P_{A}^{0}:\,P_{B}^{0}=1\,:\,2\] and have mole fraction in solution 1 : 2 then mole fraction of \[A\] in vapours                                  [DPMT 2005]

    A)                 0.33       

    B)             0.25

    C)                 0.52       

    D)                 0.2

    Correct Answer: D

    Solution :

               Relationship between mole fraction of a component in the vapour phase and total vapour pressure of an ideal solution.                   \[{{y}_{A}}=\frac{{{P}_{A}}}{{{P}_{total}}}=\frac{{{x}_{A}}.P_{A}^{0}}{{{x}_{A}}.P_{A}^{0}+{{x}_{B}}.P_{B}^{0}}\]                                      \[=\frac{1\times 1}{1\times 1+2\times 2}=\frac{1}{1+4}=\frac{1}{5}=0.2\]


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