Answer:
Mole fraction of B is 0.76
Explanation:
The pressure of a mixture of gases using vapor pressure and mole fraction of each gas is:
P = P°aₓXa + P°bₓXb + ... + P°nₓXn
Where P is pressure of the system, P° is vapor pressure of pure gas and X is its mole fraction.
In the problem, the pressure of the mixture of two gases is 740torr, mol fraction of A is 0.24 and vapor pressure of B is 800torr, that is:
740torr = P°aₓ0.24 + 800torrₓXb
Also, the sum of mole fractions for each of the compounds in the mixture is 1, that is:
1 = Xa + Xb
As Xa = 0.24
1 = 0.24 + Xb
1-0.24 = Xb
0.76 = Xb
Mole fraction of B is 0.76