Q70 / 180 · NEET 2016 (Phase 1) · Chemistry

Which of the following statements about the composition of the vapour over an ideal 1 : 1 molar mixture of benzene and toluene is correct? Assume that the temperature is constant at 25oC . (Given vapour pressure data at 25oC , benzene = 12.8 kPa, toluene = 3.85 kPa)

  • Correct answer
    A
    The vapour will contain a higher percentage of benzene.
  • B
    The vapour will contain a higher percentage of toluene.
  • C
    The vapour will contain equal amounts of benzene and toluene.
  • D
    Not enough information is given to make a prediction.

Solution

A - benzene, B - Toluene

PT=PAo XA+PBo XB

=12.8×0.5+3.85×0.5

=6.2+1.925

=8.125

Also, mole fraction of benzene in vapour form

YA=PAo XAPT=6.28.121=0.75

And mole fraction of Toluene in vapour form

YB=1-0.75=0.25

Hence, the correct answer is option: 'A'.

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