The vapour pressure of pure benzene at a certain temperature is `640 mm Hg`. A non-volatile solid weighing `2.175g` is added to `39.0g` of benzene. The vapour pressure of the solution is `600mm Hg`. What is the molar mass of the solid substance?

Answer

`69.6g//"mole"`

Explanation

Given that,
`P^(@) = 640 mm, P_(s) = 600mm, w = 2.175 g`,
`:' (P^(@)-P_(s))/(P_(s)) = (w xx M)/(m xxW)`
`:' (640 - 600)/(600) = (2.175 xx 78)/(m xx W)`
`:' m = 65.25`