Question

Two liquids A and B form an ideal solution at temperature T. When the total vapour pressure above the solution is 400 torr, the mole fraction of A in the vapour phase is 0.40 and in the liquid phase 0.75. What are the vapour pressure of pure A and pure B at temperature T?

Answer 1

Since in vapour phase we have,

$P_A={\gamma }_A{P}_{total}$

$P_A=0.4\times 400=160$

and in liquid phase we have, $P_A=P_A^0\times x_A$

$160=P_A^0\times 0.75$,

$P_A^0=213.3torr$,

we have,

$P_{total}=P_A^0{x}_A+P_B^0{x}_B$

$400=160+P_B^{0}0.25$

$P_B^0=960torr$.