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

Step-by-step solution

Given, vapour pressure of benzene, p^ =640 ~mm Hg Vapour pressure of solution, p=600 ~mm Hg Weight of solute, w=2.175 ~g Weight of benzene, W=39.08 ~g Molecular weight of benzene, M=78 ~g Molecular weight of solute, m=? According to Raoult's law, aligned p^ -p p^ &= w M m W 640-600 640 &= 2.175 78 m 39.08 40 640 &= 2.175 78 m 39.08 m &= 16 2.175 78 39.08 m &=69.60 aligned