Question

For a binary system of ideal volatile liquids 1 and 2 , the following graph is obtained :


The total pressure of the solution when mole fraction of component 1 in liquid phase is 0.25 is:

• A. $810mmHg$
• B. $825mmHg$
• C. $850mmHg$
• D. $875mmHg$

Answer 1

The correct option is C $850mmHg$

From graph:
$\text{Vapour pressure of pure component 1 is}1000mmHg$

$\text{Vapour pressure of pure component 2 is}800mmHg$

By Raoult's Law :
$P_T=p_1^{\circ }{\chi }_1+p_2^{\circ }{\chi }_2$
where
$P_T$ is the total pressure of the solution.
$p_1^{\circ }$ is the vapour pressure of pure component 1
$p_2^{\circ }$ is the vapour pressure of pure component 2
${\chi }_1$ is the mole fraction of component 1 in liquid phase.
${\chi }_2$ is the mole fraction of component 2 in liquid phase.

At ${\chi }_1=0.25,{\chi }_2=1-0.25=0.75$
$P_T=(1000\times 0.25)+(800\times 0.75)P_T=850mmHg$