Question

A solution at ${20}^o$C is composed of $1.5$ mol of benzene and $3.5$ mol of toluene. If the vapour pressure of pure benzene 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. $38.0$ torr and $0.589$
• B. $30.5$ torr and $0.389$
• C. $35.8$ torr and $0.280$
• D. $35.0$ torr and $0.480$

Answer 1

The correct option is A $38.0$ torr and $0.589$

Let us the problem.

According to the raoult's law is used which states that for a solution of volatile liquids, the partial vapour pressure of each liquid in the solution is directly proportional to its mole fraction.

$X_{benzene}=\frac{1.5}{5}=0.3$

$X_{toluence}=\frac{3.5}{5}=0.7$

$P_T=74.7\times 0.3+0.7\times 22.3$

$=22.41+15.61$

$=38.02torr$

$Y_{benzene}=\frac{22.41}{38.02}=0.589$