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Solving Problems: A Chemistry Handbook
Chemistry: Matter and Change
121
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER 12
Example Problem 12-2
Finding the Partial Pressure of a Gas
Air is made up of four main gases: N 2 , O 2 , Ar, and CO 2 . Air pressure at sea level is approximately 760 mm Hg. Calculate the partial
pressure of oxygen, given the following partial pressures: N 2 ,
594 mm Hg; Ar, 7.10 mm Hg; and CO 2 , 0.27 mm Hg.
Use Dalton’s law of partial pressures to solve the problem.
P total ϭ P N 2
ϩ P Ar ϩ P CO 2
ϩ P O 2
P O 2
ϭ P total Ϫ P N 2
Ϫ P Ar Ϫ P CO 2
P O 2
ϭ 760 mm Hg Ϫ 594 mm Hg Ϫ 7.10 mm Hg Ϫ 0.27 mm Hg
P O 2
ϭ 158.63 mm Hg
The partial pressure of oxygen is about 159 mm Hg.
Practice Problems
5. What is the partial pressure of oxygen gas in a mixture of nitrogen gas and oxygen gas with a total pressure of 0.48 atm if the
partial pressure of nitrogen gas is 0.24 atm?
6. Find the total pressure of a mixture that contains three gases
with the following partial pressures: 6.6 kPa, 3.2 kPa, and
1.2 kPa.
7. Find the total pressure of a mixture that contains five gases with
the following partial pressures: 7.81 kPa, 13.20 kPa, 2.43 kPa,
12.50 kPa, and 2500 Pa.
8. Find the partial pressure of ammonia in a mixture of three gases
with a total pressure of 75.6 kPa if the sum of the partial pressures of the other two gases is 34.9 kPa.
You can use Dalton’s law of partial pressures to determine the
amount of gas produced by a reaction. Collect the gas in an inverted
container of water. The gas will displace the water. If the gas does
not react with the water, the total pressure inside the container will
be the sum of the partial pressures of the gas and water vapor. The
partial pressure of water vapor has a fixed value at a given temperature, which you can look up in a reference chart. You can then
calculate the partial pressure of the gas by subtracting the partial
pressure of water vapor at that temperature from the total pressure.
Solving Problems: A Chemistry Handbook
Chemistry: Matter and Change
121
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER 12
Example Problem 12-2
Finding the Partial Pressure of a Gas
Air is made up of four main gases: N 2 , O 2 , Ar, and CO 2 . Air pressure at sea level is approximately 760 mm Hg. Calculate the partial
pressure of oxygen, given the following partial pressures: N 2 ,
594 mm Hg; Ar, 7.10 mm Hg; and CO 2 , 0.27 mm Hg.
Use Dalton’s law of partial pressures to solve the problem.
P total ϭ P N 2
ϩ P Ar ϩ P CO 2
ϩ P O 2
P O 2
ϭ P total Ϫ P N 2
Ϫ P Ar Ϫ P CO 2
P O 2
ϭ 760 mm Hg Ϫ 594 mm Hg Ϫ 7.10 mm Hg Ϫ 0.27 mm Hg
P O 2
ϭ 158.63 mm Hg
The partial pressure of oxygen is about 159 mm Hg.
Practice Problems
5. What is the partial pressure of oxygen gas in a mixture of nitrogen gas and oxygen gas with a total pressure of 0.48 atm if the
partial pressure of nitrogen gas is 0.24 atm?
6. Find the total pressure of a mixture that contains three gases
with the following partial pressures: 6.6 kPa, 3.2 kPa, and
1.2 kPa.
7. Find the total pressure of a mixture that contains five gases with
the following partial pressures: 7.81 kPa, 13.20 kPa, 2.43 kPa,
12.50 kPa, and 2500 Pa.
8. Find the partial pressure of ammonia in a mixture of three gases
with a total pressure of 75.6 kPa if the sum of the partial pressures of the other two gases is 34.9 kPa.
You can use Dalton’s law of partial pressures to determine the
amount of gas produced by a reaction. Collect the gas in an inverted
container of water. The gas will displace the water. If the gas does
not react with the water, the total pressure inside the container will
be the sum of the partial pressures of the gas and water vapor. The
partial pressure of water vapor has a fixed value at a given temperature, which you can look up in a reference chart. You can then
calculate the partial pressure of the gas by subtracting the partial
pressure of water vapor at that temperature from the total pressure.