Question

At certain temperature, vapour pressure of pure element A and B has 108 and 36 torr respectively. If the solution has equal mole of A and B elements, then vapour pressure of solution is....
(A) 144 torr (B) 72 torr
(C) 90 torr
(D) 125 torr

Answer 1

Answer:

(B) 72 torr

Given:

Let Moles of B=Moles of A=n

Mole fraction of B, Yb=(n/n+n)=1/2

Pa°=36 torr

Pb°=108 torr

Ptotal=Pa°+(Pb°-Pa°)Yb

=36+(108-36)*0.5

=36+72*0.5

=36+36

=72 torr

So, correct option is (B) 72 torr