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)/(0.52)=0.2884`
`DeltaT_(f)=` molality `xxK_(f)`
`=0.02884xx1.87=0.54^(@)C`
Thus, the freezing point of the solution `=-0.54^(@)C`.