At 25 ° C the vapor pressure of benzene, C₆H₆ (78 g/mol), is 93.2 torr and that of toluene, C₇H₈ (92 g/mol), is 28.2 torr. A solution of 1.00 mol of C₆H₆ and 1.00 mol of C₇H₈ is prepared. Calculate the mole fraction of C₆H₆ in the vapor above this solution assuming the solution is ideal.

Question

Quizplus · Accepted Answer

1. Calculate the total vapor pressure of the solution using Raoult's Law:

PTotal = Xbenzene * Pbenzene + Xtoluene * Ptoluene

where X is the mole fraction and P is the vapor pressure.

PTotal = (1.00 mol / 2.00 mol) * 93.2 torr + (1.00 mol / 2.00 mol) * 28.2 torr
PTotal = 60.7 torr

2. Calculate the mole fraction of benzene in the vapor above the solution using Dalton's Law:

PBenzene = Xbenzene, vapor * PTotal

where PBenzene is the vapor pressure of benzene above the solution.

Xbenzene, vapor = PBenzene / PTotal

Xbenzene, vapor = (93.2 torr / 60.7 torr) = 0.768

Therefore, the mole fraction of benzene in the vapor above the solution is 0.768.

At 25 ° C the Vapor Pressure of Benzene, C6H6

At 25 ° C the Vapor Pressure of Benzene, C₆H₆