Question

Vapour pressure of chloroform $(CHC{l}_3)$ and dichloromethane $\left(C{H}_{2}C{l}_2\right)$ at $25^{\circ }C$ are $200mmHg$ and $41.5mmHg$ respectively. Vapour pressure of the solution obtained by mixing $25.5g$ of $CHC{l}_3$ and $40g$ of $C{H}_{2}C{l}_2$ at the same temperature will be (Molecular mass of $CHC{l}_3=119.5u$ and molecular mass of $C{H}_{2}C{l}_2=85u):$

• A. 173.9 mmHg
• B. 615.0 mmHg
• C. 347.9 mmHg
• D. 90.63 mmHg

Answer 1

Answer: (D)

Number of moles of $CHC{l}_3$,

$n_A=\frac{W}{M}=\frac{25.5}{119.5}=0.213$

Number of moles of $C{H}_{2}C{l}_2$

$n_B=\frac{40}{85}=0.47$

Mole fraction of $CHC{l}_3$

$x_A=\frac{n_A}{n_A+n_B}=\frac{0.213}{0.684}=0.31$

mole fraction of $C{H}_{2}C{l}_2$

$X_B=1-x_A$

$=1-0.31=0.69$

$P_{\text{Total}}=P_A{x}_A+P_B{x}_B$

$=200\times 0.31+41.5\times 0.69$

$=62+28.63=90.63mmHg$