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75.2 g of C(6)H(5)OH (phenol) is dissolv...

`75.2 g` of `C_(6)H_(5)OH` (phenol) is dissolved in a solvent of `K_(f) = 14`. If the depression in freezing point is `7K`, then find the percentage of phenol that dimerises.

A

`75%`

B

`80%`

C

`70%`

D

`100%`

Text Solution

Verified by Experts

The correct Answer is:
A
`{:(,2C_6H_5OH hArr ,(C_6H_5OH)_2),("Initially at equil","C","0"),(,C(1-alpha),Calpha//2):}`
Total number of moles = C-C`alpha`+(C`alpha`/2)
`=C-(Calpha)/2=(2C-Calpha)/2=(C(2-alpha))/2`
C=`"Weight"/"Molecular weight"=75.2/94`=0.8
`DeltaT_f=K_fxxm`
`rArr 7 = 14 xx 0.8 ((2-alpha)/2) or, 1=0.8(2-alpha)`
`alpha`=0.75=75%
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