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NEET Sample Paper NEET Sample Test Paper-12

  • question_answer
    A solution has a 1 : 4 mole ratio of pentane to hexane. The vapour pressures of pure hydrocarbons at \[20{}^\circ C\] are 440 mm Hg for pentane and 120 mm Hg for hexane. The mole fraction of pentane in vapour phase would be:

    A)  0.786

    B)  0.478

    C)  0.549

    D)  0.200

    Correct Answer: B

    Solution :

     \[P=P_{{{C}_{5}}{{H}_{12}}}^{o}\times {{X}_{{{C}_{5}}{{H}_{12}}}}+P_{{{C}_{16}}{{H}_{14}}}^{o}\times {{X}_{{{C}_{6}}{{H}_{14}}}};\] \[P=440\times \frac{1}{5}+120\times \frac{4}{5}=\frac{920}{5}=184\] \[{{y}_{{{C}_{5}}{{H}_{12}}}}=\frac{{{P}_{{{C}_{5}}{{H}_{12}}}}}{{{P}_{t}}}\] Now, \[{{Y}_{{{C}_{5}}{{H}_{12}}}}=\frac{88}{184}=0.478\]


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