Liquid A and B form an ideal solution at 30oC. At this temperature vapour pressure of pure A and pure B is 200 mm Hg and 50 mm Hg respectively. Calculate the vapour pressure of the solution at same temperature if equal weight of A and B are added. (Given: Molecular mass of A and B are 40 and 60 respectively)
Answer & explanation
Correct answer: option 3
nA = \(\frac{x}{40}\), nB = \(\frac{x}{60}\)
XA = \(\frac{n_A}{n_A + n_B}\)
XA = \(\frac{\frac{x}{40}}{\frac{x}{40} + \frac{x}{60}}\) = 0.6
and XB = 1 - 0.6 = 0.4
PT = PA + PB = PoAXA + PoBXB = 200 x 0.6 + 50 x 0.4 = 120 + 20 = 140 mm Hg