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The depression in the freezing point of ...

The depression in the freezing point of a benzene solution containing 0.784g of Acetic acid dissolved in 100ml of benzene is 0.35k. Calculate the van't Hoff factor and the degree of association of the solute at this concentration
`(k_(f)" for benzene = 5.10 k.kg.mol"^(-1)," molar mass of acetic acid is 60.01").`

Text Solution

Verified by Experts

`DeltaT_(f)=0.35k`
`M_(2)=(k_(f).W_(2))/(DeltaT_(f).W_(1))`
`=(5.10xx0.784xx1000)/(100xx0.35)=114.0.35`
The colligative property is inversely related to molar mass.
`therefore" Van.t Hoff factor"`
`i=("Observed colligative property")/("Normal colligative property")`
`=("Theoretical molar mass")/("Observed molar mass")`
`"Van.t Hoff facotr i "=(60)/(114.24)`
`=0.525`
`"Degree pf asspcoatopm "alpha=(n(l-1))/(n-l)`
`n=2` for dimerisation
Acetic acid exist as dimers in benzene
`alpha=2((1-0.525))/(2-1)=0.95`
`therefore" Degree of association = 0.95"`
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