A solution of urea in water has boiling point of `100.15^(@)C`. Calculate the freezing point of the same solution if `K_(f)` and `K_(b)` for water are `1.87 K kg mol^(-1)` and `0.52 K kg mol^(-1)`, respectively.

Explanation

`DeltaT_(b) =(100.15 - 100) = 0.15^(@)C`
We know that `DeltaT_(b) = "Molality" xx K_(B)`
Molality `= (DeltaT_(b))/(K_(B)) = (0.15)/(0.50) = 0.2884`
`DeltaT_(b) = "Molality" xx K_(f)`
`= 0.2884 xx 1.87`
`= 0.54^(@)C`
Thus, the freezing point of the solution `= -0.54^(@)C`