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RAJASTHAN ­ PET Rajasthan PET Solved Paper-2008

  • question_answer
    On adding a non-volatile solution in a solvent, the vapour pressure of solvent reduces 10 mm of Hg. The mole fraction of solute is 0.2 in the solution. The vapour pressure of solution reduces to 20 mm of Hg on adding more solute in the solution. Now, what will the mole fraction of solvent in solution?

    A)  0.2               

    B)  0.4

    C)  0.6              

    D)  0.8

    Correct Answer: C

    Solution :

     According to Raoult's law, lowering of vapour pressure ocmole fraction of solute. \[\frac{10\,mm}{20\,mm}=\frac{0.2}{X}\] \[X=\frac{0.2\times 20}{10}=0.4\] Here,      \[X=\]mole fraction of solute \[\therefore \]mole fraction of solvent \[=1-0.4\]      \[=0.6\]


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