Question

Two liquids $A$ and $B$ form an ideal solution. What is the vapour pressure of solution containing $2$ moles of $A$ and $3$ moles of $B$ at $300K$?

[Given: At $300K$, vapour pressure of pure liquid $A\left(P_A^{\circ }\right)=100torr$, Vapour pressure of pure liquid $B\left(P_B^{\circ }\right)=300torr]$.

• A. $200torr$
• B. $220torr$
• C. $180torr$
• D. None of these

Answer 1

Answer: (B)

$220torr$

$x_A=\frac{2}{2+3}=\frac{2}{5},x_B=\frac{3}{5}$

Vapour pressure of solution

$=x_A{P}_A^o+x_B{P}_B^o$ [Raoult's Law]

$=\frac{2}{5}\times 100+\frac{3}{5}\times 300$

$=220$ $torr$