At a given temperature, the vapor pressure of heptane is 92.0 torr and the vapor pressure of octane is 31.2 torr. Assuming ideal behavior, what is the vapor pressure of a solution that contains three times as many moles of octane as heptane?
A) 87.3 torr
B) 52.4 torr
C) 76.8 torr
D) 46.4 torr
E) none of these

Question

Quizplus · Accepted Answer

The vapor pressure of the solution is calculated using Raoult's Law: P_solution = X_heptane * P_heptane + X_octane * P_octane. With three times as many moles of octane, X_heptane = 1/4 and X_octane = 3/4. Thus, P_solution = (1/4 * 92.0) + (3/4 * 31.2) = 46.4 torr.

At a Given Temperature, the Vapor Pressure of Heptane Is