Question

Solution x contains 30 mole percent of a and is equilibrium with its vapour that contains 40 mmole percent of

b. the ratio of pure a and b

Answer 1

From Raoult's law

PA = (P*A) x (χA)

PB = (P*B) x (χB)  ; χB is mole fraction B in LIQUID phase


and from Daltons law

PA = yA x Ptotal

PB = yB x Ptotal  ; yB is mole fraction B in VAPOR phase

Subbing values we get,

yA x Pt = (P*A) x (χA)

yB x Pt = (P*B) x (χB)

Dividing these equations we get

(yA / yB) x (Pt / Pt) = (P*A / P*B) x (χA / χB)

simplifying and rearranging

(P*A / P*B) = (yA / yB) x (χB / χA)

(P*A / P*B) = (60 / 40) x (70 / 30) = 3.5

Ratio of pure a and b = 3.5