Question

In a mixture of volatile substances, the vapor pressure of the solution depends on the vapor pressure of both substances (solute and solvent). Each component can evaporate, but its vapor pressure is lowered by the presence of the other substance following Rault's law. The vapor pressure of the solvent is calculated using Psolvent = Xsolvent*Posolvent and the vapor pressure of the solute is calculated using Psolute = Xsolute*Posolute. The total vapor pressure can be calculated by Dalton's law of partial pressures, Ptotal = Psolvent + Psolute.At 25oC, the vapor pressure of pure benzene (C6H6, 78.11 g/mol) is 96 torr. At the same temperature, the vapor pressure of pure toluene (C7H8, 92.14 g/mol) is 14 torr. Consider a solution containing 2.15 mol of benzene and 8.53 mol of toluene. Calculate the vapor pressure above the solution. Enter your answer in units of torr to three significant figures.

Answer 1

Answer:

30.4 torr

Explanation:

We have all the information which is required to solve this question ( more than we even need as the molecular weight)

Ptotal = Ptoluene + Pbenzene

Ptotal = Xtoluene Pºtoluene + XbenzenePºbenzene

The mole fraction is given by the formula:

X =number of moles / total number of moles

Xtoluene = 8.53 / (2.15+8.53) = 0.80

Xbenzene = 2.15 / 10.68 = 0.20

⇒Ptotal = 0.80 x 14torr + 0.20 x 96 torr = 30.4 torr