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Phenol associates in benzene to a certain extent to form a dimmer. A solution containing20 g of phenol in 1.0 kg of benzene has its freezing point lowered by 0.69 K. Calculate thefraction of phenol that has dimerised. [Given K_f for benzene = 5.1 K m^(-1) |
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Answer» SOLUTION :`M_2` (OBSERVED) ` = (1000 K_f w_2)/(w_1 Delta T_f)` SUBSTITUTING the values , we have `M_2 = (1000 XX 5.12 xx 2 xx 10^(-2) )/(1.0 xx 0.69) = 148.g "mol"^(-1)` `M_2` (calculated ) = 94 g/mol`i=(M_2("calculated"))/(M_2("observed") = (94)/(148.4) = 0.633` The association can be EXPRESSED as under  where `alpha ` is the degree of association `i= (1 - alpha//2)/(1) " or" alpha = 2(1 - i) = 2(1-0.633)= 0.734` |
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