Q12 of 26 Page 1

3.9 g of benzoic acid dissolved in 49 g of benzene shows a depression in freezing point of1.62K. calculate the van’t Hoff factor and predict the nature of solute (associated/ dissociated). [ Given: molar mass of benzoic acid = 122 g mol-1 , Kf(H2O) = 1.86 K Kg mol-1]

Given: weight of solvent = w1 = 49 g


Weight of solute = w2 = 3.9 g


Depression in freezing point = ∆Tf = 1.62K


molar mass of benzoic acid = M2 = 122 g mol-1


Kf(H2O) = 1.86 K Kg mol-1




Since the vant Hoff’s factor ‘i’ > 1 the solute benzoic acid undergoes partial dissociation in benzene.


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