Question

The vapour prerssure of pure liquids A and B are $400$ and $600mmHg$, respectively at $298K$. On mixing the two liquids, the sum of their initial volumes is equal to the volume of the final mixture. The mole fraction of liquids B is $0.5$ in the mixture. The vapour pressure of the final solution,the mole fraction of components A and B in vapour phase, respectively are:

• A. $500mmHg,0.5,0.5$
• B. $450mmHg,0.4,0.6$
• C. $450mmHg,0.5,0.5$
• D. $500mmHg,0.4,0.6$

Answer 1

The correct option is D $500mmHg,0.4,0.6$

$P_{total}=X_A.P_A^0+X_B.P_B^0=0.5\times 400+0.5\times 600=500mmHg$

Now, mole fraction of A in vapour,

$Y_A=\frac{P_A}{P_{total}}=\frac{0.5\times 400}{500}=0.4$

and mole fraction of B in vapour,

$Y_B=1-0.4=0.6$

Hence, the correct option is $D$