On dissolving 0.5 g of non-volatile, non-ionic solute to 39 g of benzene, its vapour pressure decreases from 650 mm of Hg to 640 mm of Hg. The depression of freezing point of benzene (in K) upon addition of the solute is __________.
(Given data: Molar mass & molar freezing point depression is 78 g `mol^(-1) & 5.12 K kg mol^(-1)`]

Answer

1.02

Explanation

`(P^(0)-P_(S))/(P_(S))=i[(n_("Solute"))/(n_("solvent"))]`
`(650-640)/640=1xx(0.5xx78)/(Mxx39)rArr M_("Solute")=64 gm`
`DeltaT_(f)=K_(f)xxm=5.12xx(0.5xx1000)/(64xx39)`
`rArr DeltaT_(f)=1.02`