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Phenol associates in benzene to a certain extent to form a dimer. A solution containing 20 g of phenol in 1.0 kg of benzene has its freezing point lowered by 0.69 K. Calculate the fraction of phenol that has dimerised. [Given : K_(f) for benzene = 5.1 Km^(-1)] |
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Answer» Solution :Association of phenol `C_(6)H_(5)OH (M_(B) = 94)` `W_(B)=20` g ( Phenol ) `DeltaT_(F) `=0.69 K `W_(A) =1` kg (Benzene fraction) `K_(f) =5.1 km^(-1)` Phenol dimerised `DeltaT_(f)= iK_(f)m` `0.69=ixx5.1xx(20)/(94xx1)` `i =(94xx0.69)/(20xx5.1)` `=(64.86)/(102.51)` =0.63 `alpha=(i-1)/((1)/(n)-1)` (Association) `=(0.63-1)/((1)/(2)-1)=(0.37)/(-0.5)` `alpha=0.74` or `= 74%` |
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