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Phenol (C(6)H(5)OH) gets associated in w...

Phenol `(C_(6)H_(5)OH)` gets associated in water to from double molecules. 0.6677 g of phenol dissolved in 35.5 g of water depresses the freezing point of water by 0.215. (`K_(f) "for water"=1.86 K kg^(-1)mol^(-1)`). Calculate
Observed molar mass of phenol
Degree of association of phenol.

Text Solution

Verified by Experts

The correct Answer is:
162/47 g `mol^(-1)`; 0.842
`Step I."Calculation of observedmolar mass of phenol."`
`M_(B)=(K_(f)xxW_(B))/(DeltaT_(f)xxW_(A))`
`K_(f)=1.86" K kg mol"^(-1),W_(B)=0.6667 g, DeltaT_(f)=0.215 K, W_(A)=35.5=0.0355 kg.`
`M_(B)=((186" K kg mol"^(-1))xx(0.6667g))/((0.215K)xx(0.0355 "kg"))=162.47" g mol"^(-1)`
Step II. Calculation of Van't Hoff factor (i).
`i=("Normall molar mass of phenol"(C_(6)H_(5)OH))/("Observed molar mass of phenol")=((94"g mol"^(-1)))/((162.47" g mol"^(-1)))=0.579`
Step III. Calculation of degree of association of phenol.
`alpha=(i-1)/(1/n-1)=((0.579-1))/((0.5-1))=((-0.421))/((-0.5))=0.842.`
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