A solution of urea boils at `100.18^(@)C` at the atmospheric pressure. If `K_(f)` and `K_(b)` for water are `1.86` and `0.512K kg mol^(-1)` respectively, the above solution will freeze at,

Options

A. `-6.54^(@)C`
B. `6.54^(@)C`
C. `0.654^(@)C`
D. `-0.654^(@)C`

Answer

D

Explanation

`DeltaT_(f)=K_(f)xx" molality of solution"`
`DeltaT_(b)=K_(b)xx" molality of solution"`
`"or "(DeltaT_(f))/(DeltaT_(b))=(K_(f))/(K_(b))`
`:.(DeltaT_(f))/(0.18)=(1.86)/(0.512)`
`DeltaT_(f)=0.6539~0.654`
`DeltaT_(f)=T_(1)-T_(2)`
`rArr0.654=0^(@)C-T_(2)`
`:.T_(2)=-0.654^(@)C`
`(T_(2) to "freezing point of aqueous urea solution")`