Question

A solution at $20^{\circ}$C is composed of $1.5\, mol$ of benzene and $3.5\, mol$ of toluene. If the vapour pressure of pure benzene and pure toluene at this temperature are $74.7$ torr and $22.3$ torr, respectively, then the total vapour pressure of the solution and the benzene mole fraction in equilibrium with it will be, respectively :

• A. 35.0 torr and 0.480
• B. 38.0 torr and 0.589
• C. 30.5 torr and 0.389
• D. 35.8 torr and 0.280

Answer 1

Answer: (B)

38.0 torr and 0.589

Answer 2

$P _{\text {mix }}= P_{A}^{ \circ } \times A+P_{B}^{ \circ } X_{B}=74.7 \times \frac{1.5}{5}+22.3 \times \frac{3.5}{5}$
$=38 .$ And $y_{\text {benzene}}=\frac{22.41}{38}=0.589$