Question

Vapour pressure of benzene at 30°C is 121.8 mm. When 15 g of a non-volatile solute is dissolved in 250 g of benzene. its vapour pressure is decreased to 120.2 mm. The molecular weight of the solute is

(a) 35.67 g

(b) 355.5 g

(c) 432.8 g

(d) 502.7 g

Answer 1

Correct option (b) 355.5 g

Explanation:

P^o =  vap. pressure of pure component

P = vap. pressure in solution

w =  mass of solute, m = mol. wt. of solute W = mass of solvent, M = mol . wt. of solvent