Ch.13 - Solutions

Problem 73d

Previous problem

Next problem

Chapter 13, Problem 73d

A solution contains 50.0 g of heptane (C₇H₁₆) and 50.0 g of octane (C₈H₁₈) at 25 °C. The vapor pressures of pure heptane and pure octane at 25 °C are 45.8 torr and 10.9 torr, respectively. Assuming ideal behavior, answer the following: d. Why is the composition of the vapor different from the composition of the solution?

Verified Solution

Video duration:

This video solution was recommended by our tutors as helpful for the problem above.

Was this helpful?

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Raoult's Law

Raoult's Law states that the vapor pressure of a solvent in a solution is directly proportional to the mole fraction of the solvent in the solution. This principle helps explain how the presence of different components in a solution affects the overall vapor pressure, leading to variations in the composition of the vapor compared to the liquid phase.

Vapor-Liquid Equilibrium

Vapor-liquid equilibrium refers to the state where the rate of evaporation of a liquid equals the rate of condensation of its vapor. In a mixture of volatile liquids like heptane and octane, the equilibrium composition of the vapor will differ from that of the liquid due to differences in their individual vapor pressures and mole fractions.

Ideal Solutions

An ideal solution is one where the interactions between different molecules are similar to those between like molecules, leading to predictable behavior according to Raoult's Law. In the case of heptane and octane, assuming ideal behavior allows us to use their vapor pressures to determine how their mixture will behave, including the differences in vapor composition.

Recommended video:

Solution Components

Related Practice

Which solution has the highest vapor pressure? a. 20.0 g of glucose (C₆H₁₂O₆) in 100.0 mL of water b. 20.0 g of sucrose (C₁₂H₂₂O₁₁) in 100.0 mL of water c. 10.0 g of potassium acetate KC₂H₃O₂ in 100.0 mL of water

Calculate the vapor pressure of a solution containing 24.5 g of glycerin (C₃H₈O₃) in 135 mL of water at 30.0 °C. The vapor pressure of pure water at this temperature is 31.8 torr. Assume that glycerin is not volatile and dissolves molecularly (i.e., it is not ionic), and use a density of 1.00 g/mL for the water.

3149

views

Open Question

A solution contains naphthalene (C10H8) dissolved in hexane (C6H14) at a concentration of 12.35% naphthalene by mass. Calculate the vapor pressure of hexane above the solution at 25 °C. The vapor pressure of pure hexane at 25 °C is 151 torr.

Textbook Question

A solution contains a mixture of pentane and hexane at room temperature. The solution has a vapor pressure of 258 torr. Pure pentane and hexane have vapor pressures of 425 torr and 151 torr, respectively, at room temperature. What is the mole fraction composition of the mixture? (Assume ideal behavior.)

A solution contains 4.08 g of chloroform (CHCl3) and 9.29 g of acetone (CH3COCH3). The vapor pressures at 35 °C of pure chloroform and pure acetone are 295 torr and 332 torr, respectively. Assuming ideal behavior, calculate the vapor pressures of each of the components and the total vapor pressure above the solution. The experimentally measured total vapor pressure of the solution at 35 °C is 312 torr. Is the solution ideal? If not, what can you say about the relative strength of chloroform–acetone interactions compared to the acetone–acetone and chloroform–chloroform interactions?

Open Question

A solution of methanol and water has a mole fraction of water of 0.312 and a total vapor pressure of 211 torr at 39.9 °C. The vapor pressures of pure methanol and pure water at this temperature are 256 torr and 55.3 torr, respectively. Is the solution ideal? If not, what can be inferred about the relative strengths of the solute–solvent interactions compared to the solute–solute and solvent–solvent interactions?