The freezing point of nitrobenzene is 278.8 K. A 0.25 molal solution of a substance (molecular weight : 120) in nitrobenzene has a freezing point of 276.8 K. Calculate the molal depression constant of nitrobenzene.

Explanation

Given Normal freezing point of nitrobenzene `(C_(6)H_(5)NO_(2))=278.82K`
molality of solution `=0.25m`
Freezing point depression `=2` degrees
Asked Cryoscopic constant `=?`
Formulae: `DeltaT_(f)=K_(f)xxm`
Explanation: `DeltaT_(f)=` Freezing point depression
`K_(f)=` cryoscopic constant
`m=` molality of solution
Substitution `&` Calculation
`2=K_(f)xx0.25`
`K_(f)=(2)/(0.25)=8K kg "mol"^(-1)`