The vapor pressure of pure ethanol at 60 °C is 0.459 atm.Raoult's Law predicts that a solution prepared by dissolving 10.0 mmol naphthalene (nonvolatile)in 90.0 mmol ethanol will have a vapor pressure of ________ atm.
A)0.498
B)0.413
C)0.790
D)0.367
E)0.0918

Question

Quizplus · Accepted Answer

Since naphthalene is nonvolatile and does not contribute to the vapor pressure, the measured vapor pressure will only depend on the ethanol. 
According to Raoult's law, P(solution) = X(ethanol) * P(ethanol), where X is the mole fraction of ethanol. 
The mole fraction of ethanol is: 
X(ethanol) = 90.0 mmol / (10.0 mmol + 90.0 mmol) = 0.900 
Substituting this into the equation and using P(ethanol) = 0.459 atm: 
P(solution) = 0.900 * 0.459 atm = 0.413 atm 
Therefore, the answer is B.

The Vapor Pressure of Pure Ethanol at 60 °C Is