An ideal solution of A and B has $p_{A}^{0} = 200 torr$ and $p_{B}^{0} = 100 torr$ . The vapour in equilibrium with it contains equal mole fractions of A and B ( $y_{A} = 0.5$ ). Find the total vapour pressure of the solution in torr (two decimal places).

Numerical answer type, answer in torr, tolerance 0.01.

Answer: 133.33 torr

y_{A} = p_{A} / P = 0.5

means

p_{A} = p_{B}

, i.e.

200 x_{A} = 100 (1 - x_{A})

, so

x_{A} = 1/3

. Then

P = 200 \times \frac{1}{3} + 100 \times \frac{2}{3} = 133.33 torr