12.2 g of benzonic acid (molar mass = 122 ) in 100 g of benzene has a depression in freezing point 2.6^(@). If there is 100 percent polymersation, what is the nunber of molecues of benzoic acid in associated state ? (Given K_(f) for benzene =5.2 K kh mol^(-1))

12.2 g of benzonic acid (molar mass = 122 ) in 100 g of benzene has a

1.	12.2 g of benzonic acid (molar mass = 122 ) in 100 g of benzene has a depression in freezing point 2.6^(@). If there is 100 percent polymersation, what is the nunber of molecues of benzoic acid in associated state ? (Given K_(f) for benzene =5.2 K kh mol^(-1))
Answer» Solution :Observed molar mass of benzoic ACID MAY be CALCULATED as FOLLOWS : `M_(B)=(K_(f)xxW_(B))/(DeltaT_(f)xxW_(A))` `W_(B)=12.2g, W_(A)=100g=0.1 kg, K_(f)=5.2" K kg mol"^(-1), DeltaT_(f)=2.6 K` `M_(B)=((5.2" K kg mol"^(-1))xx(12.2 g))/((2.6 K)xx(0.1"kg"))=244.0" g mol"^(-1)` `"On comparison, observed molar mass "(244" g mol"^(-1)) "of benzoic acid is twice its normal molar mass (122" g mol"^(-1))`. This means that benzoic acid exists as a dimer in the associated state.