A solution has a 1 : 4 mole ratio of pentane to hexane. The vapour pressures of the pure hydrocarbons at 20oC are 440 mm Hg for pentane and 120 mm Hg for hexane. The mole fraction of pentane in the vapour phase would be
The vapour pressure of two liquids P and Q are 80 and 60 torr, respectively. The total vapour pressure of solution obtained by mixing 3 mole of P and 2 mole of Q would be
A
72 torr
B
140 torr
C
68 torr
D
20 torr
Explanation
Hence total vapour pressure
= [(Mole fraction of P) × (Vapour pressure of P)]
+ [(Mole fraction of Q) × Vapour pressure of Q)]