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The mole fraction of methanol is in 4.5 ...

The mole fraction of methanol is in 4.5 molal aqueous solution is

A

`0.250`

B

`0.125`

C

`0.100`

D

`0.075`

Text Solution

Verified by Experts

The correct Answer is:
D
Mole fraction, `x=((w)/(m))/((w)/(m)+(W)/(M))`
(where, w and m represent the mass and molar mass of solute and W and M represent the mass and molar mass of solvent.)
`(1)/(x)=((w)/(m)+(W)/(M))/((w)/(m))`
`(1)/(x)=1+(Wxxm)/(Mxxw)xx(1000)/(1000)`
`(1)/(x)=1+(1000)/(Mxxm)(because" Molality, "m=(wxx1000)/(mxxW))`
`=1+(1000)/(18xx4.5)` (`because` Molar mass of `H_(2)O=18g mol^(-1)`)
`=1+(1000)/(81)`
`=(1081)/(81)=13.34`
`x=(1)/(13.34)=0.075`
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