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Pure benzene freezes t 5.3^(@)C. A solut...

Pure benzene freezes t `5.3^(@)C`. A solution of 0.223 g of phenylacetic acid `(C_(6)H_(5)CH_(2)COOH)` in 4.4 g of benzene ` (K_(f) = 5.12 Kkg mol^(-1))` freezes at `4.47^(@)C`. From the observation one can conclude that :

A

Phenylacetic acid exists as such in benzene

B

Phenylacetic acid undergoes partial ionization in benzene

C

Phenylacetic acid undergoes complete ionization in benzene

D

Phenylacetic acid dimerizes in benzene

Text Solution

Verified by Experts

The correct Answer is:
D
`DeltaT_(f)=T_(0)-T_(f)=5.3-4.47=0.83`
Molality of solvent `m=(0.223)/(136)xx(1000)/(4.4)=0.373`
(Molecular weight of phenylacetic acid = 136)
`K_(f)=5.12`
`DeltaT_(f)=i.K_(f)m`
`i=(DeltaT_(f))/(K_(f)m)=(0.83)/(5.12xx0.373)=0.45`
i is nearly equal to 0.5 it means phenylacetic acid undergoes dimerization in benzene.
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