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Manipal Engineering Manipal Engineering Solved Paper-2009

  • question_answer
    Vapour pressure of pure A is 70 mm of\[Hg\]at\[{{25}^{o}}C\]. It forms an ideal solution with B in which mole fraction of A is 0.8. If the vapour pressure of the solution is 84 mm of Hg at\[{{25}^{o}}C\], the vapour pressure of pure B at\[{{25}^{o}}C\]is

    A)  28mm                                 

    B)  56mm

    C)  70mm                 

    D)         140mm

    Correct Answer: D

    Solution :

                     \[p=p_{A}^{\text{o}}{{x}_{A}}+p_{B}^{\text{o}}{{x}_{B}}\] \[\Rightarrow \]               \[84=70\times 0.8+p_{B}^{\text{o}}\times 0.2\]                 \[84=56+p_{B}^{o}\,\times 0.2\]               \[p_{B}^{\text{o}}=\frac{28}{0.2}=140\,\,mm\]


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