The vapour pressure of benzene at a certain temperature is 640 mm of Hg. A non-volatile electrolyte solute weighing 2.175 g is added to 30.08 g of benzene. If the vapour pressure of the solution is 600 mm of Hg, what is the molecular weight of the solid substance?

0 0 P P w M m W P x x 0 vapour pressureof puresolvent(640mm Hg) P vapour pressureof solution (600mm Hg) w weight of solute(2.175gm) W weight of benzene(30.08gm) M molecular weight of benzene(78gm) P On substituting the values 640 600 2.175 78 640 m 30.08 x x Molecular weight = 90.23 g/mol