Question

Liquid $A(p_A^0=200\text{mm of Hg})\text{and}B(P_B^0=100\text{mm of Hg})$ forms ideal solution. If the vapour pressure of solution is $180\text{mm of Hg}$, the mole fraction of the liquid $A$ in the solution is:
[0.77 Mark]

• A. $0.2$
• B. $0.4$
• C. $0.6$
• D. $0.8$

Answer 1

The correct option is D $0.8$

$P_T=x_A{P}_A^0+x_B{P}_B^0$
$=x_A{P}_A^0+(1-x_A)P_B^0$
$=x_A{P}_A^0+P_B^0-x_A{P}_B^0$
$=P_B^0+(P_A^0-P_B^0)x_A$.......(i)
On putting the values in equation(i)
$180=100+(200–100)\times x_A$
$x_A=0.8$