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Punjab Medical Punjab - MET Solved Paper-2005

  • question_answer
    Mole fraction of a solute in benzene is 0.2 then find molality of solute:

    A) \[3.2\]                                  

    B) \[2\]

    C) \[4\]                                     

    D) \[3.6\]

    Correct Answer: A

    Solution :

    Let the solution be \[x\] molal then moles of solute present in 1000 g of benzene \[=\frac{1000}{78}=12.82\,\,moles\]. \[\therefore \]Mole fraction of solute\[=\frac{x}{x+12.82}\]                                           \[0.2=\frac{x}{x+12.82}\]                       \[0.2(x+12.82)=x\]                          \[0.2x+2.564=x\]                                      \[2.564=x-0.2x\]                                                    \[=0.8x\]                                                 \[x=\frac{2.564}{0.8}=3.2\]


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