Question

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 moles of P and 2 moles of Q would be:

• A. 144 torr
• B. 288 torr
• C. 14 torr
• D. 72 torr

Answer 1

Answer: (D)

72 torr

Answer 2

The following is the formula for determining a solution's vapour pressure:
PT = PP0P +PQ0Q
Where PT is the solution's vapour pressure
PP = Liquid 'P' at its purest condition vapour pressure
PQ is equal to the liquid 'Q's pure vapour pressure.
P is the solution's mole fraction of liquid P.
Q equals the mole fraction of liquid Q in the mixture.
In response to this query, PP = 80 PQ = 60 moles of P = 3 and Q = 2 in the solution,
thus the total number of moles is 5 P = 0.6 Q = 0.4. PT = 80 x 0.6+ 60 x 0.4 = 72.

Therefore, the correct option is (D): 72 torr