Liquid A and B form an ideal solution at 30^oC. At this temperature, vapour pressure of pure A and pure B is 200 mm Hg and 50 mm Hg respectively. What is the vapour pressure of the solution if Equal weight of A and B is added? (Given: Molecular mass of A and B are 40 and 60 respectively) 

140 mm Hg

nA = \(\frac{x}{40}\) , nB = \(\frac{x}{60}\)

Χ_A = \(\frac{nA}{nA + nB}\) = \(\frac{x/40}{x/40 + x/60}\) = 0.6

and X_B = 1 - 0.6 = 0.4

P_T = P_A + P_B = P^o_AX_A + P^o_BX_B = 200 x 0.6 + 50 x 0.4 = 120 + 20 = 140 mm Hg