Question

The vapour pressure of two liquids $P$ and $Q$ are $80$ and $60\text{torr}$, respectively. The total vapour pressure of the ideal solution obtained by mixing $3$ mole of $P$ and $2$ mol of $Q$ would be:

• A. $72\text{torr}$
• B. $140\text{torr}$
• C. $68\text{torr}$
• D. $20\text{torr}$

Answer 1

The correct option is A $72\text{torr}$

$\text{By Raoult's Law,}{P}_T=P_p^{\circ }{X}_P^{\circ }+P_Q^{\circ }{X}_Q$
$\text{Where,}{P}_p^{\circ }=80\text{torr},P_Q^{\circ }=60\text{torr},X_p=\frac{3}{5};X_Q=\frac{2}{5}$
$P_T=80\times \frac{3}{5}+60\times \frac{2}{5}=48+24=72torr$