The vapour pressure of pure benzene at a certain temperature is 640 mm of Hg. A non volatile nonelectrolyte solid weight 0.175 g is added to 39.0 benzene. The Vapour pressure of the solution is 600 mm of Hg. What is molecular weight of solid substance?

Answer

65.25

Explanation

Benzene- A , solute-B
`(P_(A)^(0)-P_("solution"))/(P_(A)^(0))=(w_(B)//m_(B))/(w_(B)//m_(B)+w_(A)//m_(A))`
`(640-600)/(640)=((2.175)/(m_(B)))/((2.175)/(m_(B))+(39)/(78)`
`m_(B)=65.25"gm mol"^(-1)`