Question

A solution of urea (molecular mass = 60 g `mol^(-1)`) boils at `100.18^(@)C` at 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 :
A. `0.654^(@)C`
B. `-0.654^(@)C`
C. `6.54^(@)C`
D. `-6.54^(@)C`

Answer 1

Correct Answer - b
`(DeltaT_(f))/(DeltaT_(b))=K_(f)/K_(b)`
`DeltaT_(f)=DeltaT_(b)=(0.18^(@))xx(1.86)/(0.512)=0.654^(@)C`
Freezing point of solution
= `0-0.654^(@)C=-0.654^(@)C`