3.9 g of benzoic acid dissoved in 49 g of benzene shows a depression in freezing point of 1.62 K. Calculate Van't Hoff factor and predict the nature of solute (associated or dissociated) . (Given. Molar mass of benzoic acid = 122 g `mol^(-1)` , `K_(f)` for benzene = 4.9 K kg `mol^(-1)`).

Answer

0.506, Associated

Explanation

`i=(DeltaT_(f))/(K_(f)xxm)DeltaT_(f)=1.62 K, K_(f)=4.9" K kg mol"^(-1), M=((3.9g)//(122" g mol"^(-1)))/((0.049 kg))`
`i=(1.62Kxx(0.049" kg")xx(122" g mol"^(-1)))/((4.9"K kg mol"^(-1))xx(3.9g))=0.506`
Scince Van't Hoff factor is less than 1, solute has undergone has undergone associated in benzene solvent.