1. Dalton’s Law of Partial Pressures
States – that the total pressure of a gas mixture is the sum of the partial pressures of the component gases.
The pressure of each gas in a mixture is called partial pressure.
PT = P1 + P2 + P3 + ….
PT is the total pressure of the mixture. P1 etc are the partial pressures of component gases

2. Gases collected by water displacement
When gases are collected by displacing water in a container there is always some water vapor mixed with the gas collected.
To determine the total pressure of the gas and water vapor inside a collection bottle ;
Patm = P gas + P H2O
Patm – given atmospheric pressure
Pgas – total pressure PH2O – water vapor pressure

3. Gases collected by water displacement
The PH2O – water vapor pressure at a certain temperature can be found in the book on page 859 table A-8.
This means that at different temperatures the water vapor pressure is different.

4. Gases collected by water displacement
Oxygen gas from the decomposition of KClO3, was collected by water displacement. The barometric pressure and the temperature during the experiment were 731 torr and 20oC, respectively. What was the partial pressure of the O2 collected?
P atm = 731 torr
PH2O = (table A-8 on page 859)
water vapor at 20oC = 17.5 torr
Patm = P O2 + P H2O
Unk: PO2 in torr
PO2 = Patm – PH2O or
Po2 = 731 torr – 17.5 torr = torr

5. If carbon dioxide, nitrogen, and oxygen are in a container and exert a pressure of 760 torr, and the partial pressure of carbon dixoide is torr, the partial pressure of nitrogen is torr, what is the partial pressure of oxygen?

6. Table A-8 page 859
2. Calculate the partial pressure of oxygen collected by water displacement if the water temperature is 20oC and the total pressure of the gases in the collection bottle
is mm Hg.

7. 3. A sample of gas is collected over water at a temperature of 35
3. A sample of gas is collected over water at a temperature of 35.0oC when the barometric pressure reading is mm Hg. What is the partial pressure of the gas?

8. 4. A sample of gas is collected over water at a temperature of 27oC
4. A sample of gas is collected over water at a temperature of 27oC. The atmospheric pressure is kPa. What is the pressure of the gas collected?