Raoult’s law states partial pressure of a component in a solution is equal to its mole fraction multiplied by the vapor pressure of that component in pure state.
P = P0.X
P- V.P of component in the solution, P0– V.P of pure solvent, X-mole fraction of the component.
The total vapor pressure of a solution for two individual components A and B can be given by
P = PA + PB = P0A.XA + P0B.XB
The sum of mole fraction of all the components in a solution is unity.
XA + XB = 1
P = P0A.(1-XB) + P0B.XB = (PB0 – P0A)XB + P0A
Vapor pressure of pure “A” is 70 mm of Hg at 25˚C. It forms an ideal solution with “B” in which mole fraction of A is 0.8. If the vapor pressure of the solution is 84mm of Hg at 25˚C, the vapor pressure of pure “B” at 25˚C is:
The mole fraction of B = 1 – Xa = 1- 0.8 = 0.2
According to Raoult’s law, P = PA + PB = PA0XA + PB0XB