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An ideal solution was found to have a va...

An ideal solution was found to have a vapour pressure of 80 torr when the mole fraction of a non-volatile solute was 0.2. What would be the vapour pressure of the pure solvent at the same temperature?

A

150 mm of Hg

B

60 mm of Hg

C

75 mm of Hg

D

120 mm of Hg

Text Solution

Verified by Experts

The correct Answer is:
C
We know that, according to Raoult's law
`(p^(@)-p)/(p^(@))=chi_(B)`
`(p^(@)-60)/(p^(@))=(n_(B))/(n_(A)+n_(B))=(0.2)/(0.2+0.8)`
`=(0.2)/(1.0)=(2)/(10)=(1)/(5)`
`p^(@)-60=(p^(@))/(5)`
`rArr p^(@)-(p^(@))/(5)=60`
`(5p^(@)-p^(@))/(5)=60`
`4p^(@)=60xx5`
`p^(@)=(60xx5)/(4)=(300)/(4)=75` mm of Hg
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