Question

$1$ mole benzene $\left(p_{\text{benzene }}^o=42mm\right)$ and $2$ mole toluene $\left(p_{\text{benzene }}^n=36mm\right)$ will have:

• A. Mole fraction of benzene in vapour phase above liq. Mixture is $1/3$.
• B. Mole fraction of toluene in vapour phase above liq. Mixture is $8/19$
• C. Total vapour pressure of solution is $38mm$
• D. Mole fraction of benzene in vapour phase above liquid mixture is $7/19$

Answer 1

Answer: (C), (D)

$P_{\text{total }}=P_B^o{X}_B+P_T^o{X}_T$
$=42\times \frac{1}{3}+36\times \frac{3}{2}=38mm$
$P_M{Y}_B=P_B^o\times X_B$ where $YB$ is the mole fraction of Benzene is vapour phase
$38\times Y_B=14;Y_B=\frac{14}{38}=\frac{7}{19}$
$Y_A=1-\frac{7}{19}=\frac{11}{19}$