13.2.3 Pressure Change and Solubility

Question 1

Pressure Change and Solubility

Answer 1

• Henry’s Law states that the concentration of a solute is proportional to the partial pressure of that component in the gas phase.
• Henry’s Law: [solute] = K H P or P gas = K H X gas

Question 2

note

Answer 2

• Henry’s law states that the concentration of a solute is
  proportional to the partial pressure of that component in the gas phase. The higher the concentration of the solute in solution, the higher the partial pressure of the solute above the solution will be.
• This is expressed as [solute] = K H P gas , where [solute] is the molar concentration of the solute in solution, K H is the Henry’s law constant for that solute, and P is the partial pressure of the gas above the liquid. This equation indicates a direct relationship between partial pressure and concentration.
• Another form of Henry’s law states that the partial pressure of the gas is equal to a different Henry’s law constant (K H ) times the mole fraction of the solute in the solution: P gas = K H X gas .
• Given the Henry’s law constant for oxygen dissolved in water (4.34 x 10 4 atm) and the partial pressure of oxygen (0.20 atm), the concentration of oxygen in mol/L at equilibrium can be determined.
• By using P O2 = K H(oxygen) X, the mole fraction for oxygen is obtained. There are no units on the mole fraction. The mole fraction represents the number of moles of oxygen divided by the total number of moles.
• In order to determine moles per liter, it is convenient to base the rest of the calculation on one liter of water. The problem is greatly simplified if the total number of moles in the solution is assumed to be essentially equal to the number of moles of water.
• The number of moles of water in one liter is determined by converting the volume (1.000 L) to mass (1000 g) using the density of water (1 g/mL). Dividing by the molar mass of water (18.0 g/mol) yields moles of water.
• Once the number of moles of water in a liter is determined, the number of moles of O 2 per liter is obtained from the mole fraction.

Question 3

Suppose you have an oxygen and water solution. What is the concentration (in mol / L) of the solution at 25°C and a partial pressure for oxygen of 0.25 atm? The Henry’s law constant is 4.28 × 10^3 atm.

Answer 3

3.25 × 10^−3 mol / L

Question 4

Which statement about Henry’s law is not true?

Answer 4

Because the constants for Henry’s law are for a system at constant temperature, the Henry’s law equations are not dependent on temperature.

Question 5

Which statement about the CO2 molecules in a sealed can of carbonated beverage is not true?

Answer 5

By opening the can, more CO2 vapor is absorbed by the solvent

Question 6

Which of the following best describes vapor pressure?

Answer 6

the pressure exerted by the vapor of a liquid or a solid when the vapor and the liquid or solid are in dynamic equilibrium

Question 7

Which of the following statements is not correct?

Answer 7

The gas inside a sealed can of carbonated liquid is not in equilibrium with the liquid. This is demonstrated by what happens when you open the container.

Question 8

Which of the following statements about the dynamic equilibrium that exists between a solute vapor (gas) and the solute dissolved in solution is not true?

Answer 8

There is a direct relationship between the total pressure of the vapors and the mole fraction of the solute in the solution

Question 9

Suppose that a solution of oxygen and water has a Henry’s law constant value of 3.9 × 10^3 atm at 25°C. What other value do you need in order to calculate the mole fraction of oxygen in solution?

Answer 9

Poxygen

Question 10

Use your knowledge of Henry’s law to decide which circumstance would be best for maintaining a specific concentration of CO2 gas dissolved in solution.

Answer 10

Maintain the same partial pressure of CO2 gas on the system at all times.

Question 11

Look at the drawing for a closed system of a solution and its vapor.

Which statement about this system is not true?

Answer 11

The concentration of the solute is inversely proportional to the pressure of the solute in the vapor state.

Question 12

Which of the following best describes mole fraction?

Answer 12

a ratio of the number of moles of a substance in a mixture to the total number of moles in the mixture