The vapour pressure of benzene at a certain temperature is `640 mm` of Hg A non-volatile and non-electrolyte solid weighing `2.175g` is added to `39.08g` of benzene .the vapour pressure of the solution is `600 mm` of Hg. What is the molecular weight of solid substance ?

Options

A. `49.50`
B. `59.6`
C. `69.5`
D. `79.8`

Answer

C

Explanation

`(P_(0)-P_(s))/(P_(0))=((w)/(m))/((w)/(m)+(W)/(M)) because (W)/(M)gt(w)/(m)`
`rArr(640-600)/(640)`
`=(w)/(m)xx(M)/(W)rArr(40)/(640)=(2.175xx78)/(mxx39.08)`
`m=(2.175xx78)/(39.08)xx(640)/(40)`
`m=69.45`