At `100^(@)C` the vapour pressure of a solution of `6.5g` of an solute in `100g` water is `732mm`.If `K_(b)=0.52`, the boiling point of this solution will be :

Options

A. `100^(@)C`
B. `102^(@)C`
C. `103^(@)C`
D. `101^(@)C`

Answer

D

Explanation

From Raoult's law of partial pressure,
`(p_(A)^(@)-p_(S))/(p_(S))=(n_(S))/(n_(A))`
`rArr (760-732)/(732)=(W_(B)xxM_(A))/(M_(B)xxW_(A))`
`rArr (28)/(732)=(6.5xx18)/(M_(B)xx100)`
`rArr M_(B)=30.6`
`therefore Delta T_(b)=0.52xx(6.5xx1000)/(30.6xx100)=1.10`
`therefore` Boiling point `=100+1.0=101.1^(@)C=101^(@)C`