Question

The vapour pressure of two pure liquids $A$ and $B$, that form an ideal solution are $100$ and $900$ torr respectively at temperature $T$. This liquid solution of $A$ and $B$ is composed of $1mole$ of $A$ and $1mole$ of $B$. What will be the pressure, when $1$ mole of mixture has been vapourized?

• A. $800torr$
• B. $500torr$
• C. $300torr$
• D. None of these

Answer 1

Answer: (C)

$300torr$

$P_A^o=100torr{P}_B^o=900torr$

$n_A=1mole{n}_B=1mol$

$x_A=\frac{1}{1+1}=0.5mole$

$x_B=\frac{1}{1+1}=0.5mole$

Pressure $=P_A^o{x}_A+P_B^o{x}_B$

$=100\times 0.5+900\times 0.5=50+450=500torr$