Pressure Change and Solubility (13.2.3)

Question 1

• Henry’s Law states that the concentration of a solute is proportional to the partial pressure of that component in the gas phase.

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.

Question 2

• Henry’s Law: [solute] = KHP or Pgas = KHXgas

Answer 2

• Henry’s Law: [solute] = KHP or Pgas = KHXgas

Question 3

Henry’s Law

Answer 3

X = moles solute / total moles solution

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. (C)

The constants depend directly on temperature. The constants are only accurate for one specific temperature. Therefore, for each temperature, there are new constants.

Question 5

Which of the following best describes mole fraction?

Answer 5

a ratio of the number of moles of a substance in a mixture to the total number of moles in the mixture (B)

This is a good definition of mole fraction. It is unitless because the units in the denominator and numerator are both moles, so they cancel. The mole fraction is what we sometimes refer to as concentration in this lesson.

Question 6

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 × 103 atm.

Answer 6

3.25 × 10−3 mol / L (B)

Question 7

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

Answer 7

By opening the can, more CO2 vapor is absorbed by the solvent. (C)

Question 8

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

Which statement about this system is not true?

Answer 8

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

The concentration of the solute is directly proportional to the pressure of the material in its gas state. They differ only by the Henry’s law equation constant.

Question 9

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 9

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

This statement tells you first to make sure you have a closed system. Then it suggests that you maintain the partial pressure of the CO2 gas. This is vital for maintaining the concentration of CO2 gas in solution.

Question 10

Which of the following best describes vapor pressure?

Answer 10

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

The key point here is that vapor pressure concerns the pressure exerted by the vapor of a liquid or a solid. In other words, it is a partial pressure term whenever there is other vapor involved. It is assumed that the vapor from the liquid or solid is in dynamic equilibrium with the liquid or solid.

Question 11

Suppose that a solution of oxygen and water has a Henry’s law constant value of 3.9 × 103 atm at 25°C. What other value do you need in order to calculate the mole fraction of oxygen in solution?

Answer 11

P oxygen (A)

According to Henry’s Law:

Poxygen = kH • Xoxygen

Since kH is given, to determine Xoxygen one only need Poxygen.

Question 12

Which of the following statements is not correct?

Answer 12

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. (C)

When the can is sealed, there is an equilibrium established between the gas vapor on top and the liquid. When the can is opened, the solution adjusts to the change in pressure and a new equilibrium is eventually reached.

Question 13

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 13

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

Henry’s law examines a closed system and relates the mole fraction of the solute in solution to the partial pressure of the solute vapor above the solution. The partial pressure is not the same as the total pressure. It is only the contribution of the solute vapor that affects the concentration of solute in the gas.