Total vapor pressure can be calculated using partial vapor pressures and mole fraction as follows:
Here, is mole fraction of A,
is mole fraction of B,
is partial pressure of A and
is partial pressure of B.
The mole fraction of A and B are related to each other as follows:
In this problem, A is hexane and B is octane, mole fraction of hexane is given 0.580 thus, mole fraction of octane can be calculated as follows:
Partial pressure of hexane and octane is given 183 mmHg and 59.2 mmHg respectively.
Now, vapor pressure can be calculated as follows:
Putting the values,
Therefore, total vapor pressure over the solution of hexane and octane is 131 mmHg.
