Q11 of 26 Page 1

3.9 g of benzoic acid dissolved in 49 g of benzene shows a depression in freezing point of 1.62 K. Calculate the Vant Hoff factor and predict the nature of solute (Associated or dissociated). Given molar mass of benzoic acid=122 g/mol, Kf (Benzene) = 54.9 K kg/mol.

Given, mass of solute i.e. benzoic acid, W2 = 3.9 g


Molar mass of solute, M2 = 122 g


Mass of solvent i.e. benzene, W1 = 49 g


Depression in freezing point, ΔTf = 1.62 K


We know, ΔTf = i where i = Vant Hoff factor


i =


i = 0.045


Since, the value of i<1, it shows molecular association.


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