The Colligative Properties Video Lessons

Concept:

# Problem: Pentane, C5H12 ; hexane C6H14 . The vapor pressure of an ideal mixture of pentane and hexane at room temperature contains 25.8% by mass pentane. Pure pentane and hexane have vapor pressures of 425 torr and 151 torr respectively at this temperature. What is the mass percent of pentane in the solution?A. 11.0% B. 16.4%C. 89.0% D. 24.3% E. 32.9%

###### FREE Expert Solution

We’re being asked to calculate the mass percent of pentane in the solution.

In this problem, we will be dealing with the vapor phase and the solution (liquid phase).

Let:      χ = mole fraction in the solution (liquid phase)
y = mole fraction in the vapor phase

We will calculate for the mass percent of pentane in the solution using the following steps:

Step 1: Calculate the mass of pentane and hexane in the vapor phase.
Step 2: Calculate the mole fraction pentane and hexane in the vapor phase.
Step 3: Create an equation that relates vapor pressures with mole fraction.
Step 4: Create an equation that relates vapor pressures, Dalton’s Law of Partial Pressure, and Raoult’s Law.
Step 5: Calculate for the mole fraction of pentane and hexane in the solution.
Step 6: Calculate the mass of pentane and hexane in the solution.
Step 7: Calculate for the mass percent of pentane in the solution.

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###### Problem Details

Pentane, C5H12 ; hexane C6H14 . The vapor pressure of an ideal mixture of pentane and hexane at room temperature contains 25.8% by mass pentane. Pure pentane and hexane have vapor pressures of 425 torr and 151 torr respectively at this temperature. What is the mass percent of pentane in the solution?

A. 11.0%

B. 16.4%

C. 89.0%

D. 24.3%

E. 32.9%