Question

A mixture contains 1 mole of volatile liquid $A(P_A^{\circ }=100mmHg)$ and 3 moles of volatile liquid $B(P_B^{\circ }=80mmHg)$. If solution behaves ideally, the total vapour pressure of the distillate is :

• A. $85$ mm Hg
• B. $85.88$ mm Hg
• C. $90$ mm Hg
• D. $92$ mm Hg

Answer 1

The correct option is A $85$ mm Hg

Mole fraction of A is $X_A=\frac{1}{1+3}=0.25$

The mole fraction of B is $X_B=1-0.25=0.75$

The expression for the total pressure of the solution is

$P=P_A^o{X}_A+P_B^o{X}_B$

Substitute values in the above expression

$P=100\times 0.25+80\times 0.75=85mmHg$

Hence, the correct option is $A$