4. An ideal solution contains 40 mole percent of A and 60 mole percent of B at 80 oC. The vapor pressure of pure A and B at this temperature are 480 torr and 890 torr, respectively. Calculate the vapor pressure of the solution.

Answer :  The vapor pressure of the solution is, 726 torr.

Explanation : Given,

Mole percent of A = 40 %

Mole fraction of A = 0.4

Mole percent of B = 60 %

Mole fraction of A = 0.6

Now we have to calculate the partial pressure of A and B.

According to the Raoult's law,

where,

= vapor pressure of gas

= vapor pressure of pure gas  

= mole fraction of gas

and,

Now we have to calculate the vapor pressure of the solution.

Thus, the vapor pressure of the solution is, 726 torr.