A solution of urea (mol. Mass `60 g mol^(-1)`) boils of `100.18^(@)C` at one one atmospheric pressure. If `k_(f)` and `K_(b)` for water are `1.86` and `0.512 K 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

`Delta T_(b)=0.18 , Delta T_(b)=m K_(b)`
`(0.18)/(Delta T_(f))=(mK_(b))/(m K_(f)) , (0.18xx1.86)/(0.512)=Delta T_(f) , Delta T_(f)=0.653`
`T^(+)-T_(s)=0.653 , T_(s)=0-0.653^(@)C , T_(s)=-0.653^(@)C`