Q11 of 26 Page 1

3.9g of benzoic acid dissolves in 49g of benzene shows a depression in freezing point of 1.62K. Calculate the van’t Hoff factor and predict the nature of solute (associated or dissociated).

(Given: molar mass of benzoic acid =122g mol-1, Kf of benzene =4.9K Kg mol-1)






Molar mass of solute (benzoic acid) = 122g mol-1


Mass of solute = 3.9g


Mass of solvent(benzene) = 49g





Since the value of ‘i’ <1, we can say that association occurs in these molecules. In general carboxylic acids dimerise through hydrogen bonding, hence the value of ‘i’ exactly half the ideal value.


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