1. Journal #64
What is the relationship between altitude and pressure?

2. Today, we will use Dalton’s law of partial pressures to calculate partial pressures and total pressures

3. Dalton’s Law of Partial Pressures
John Dalton studied gas mixtures
The pressure exerted by each gas in an uncreative mixture is independent of that exerted by other gases present.
The pressure of each gas in a mixture is called the partial pressure.
Dalton’s law of partial pressure states that the total pressure of a gas mixture is the sum of the pressures of the component gas.

4. Dalton’s Law Dalton’s Law may be expressed as:
PT = P1 + P2 + P3 + ….
PT is the total pressure of the mixture, P1, P2, P3 and so on are the partial pressures of component gases.

5. Kinetic Molecular Theory
Each of the moving particles of gases in mixture has an equal chance to collide with the container walls.
Therefore, each gas exerts a pressure independent of that exerted by the other gases present.
The total pressure is the result of the total number of collisions per unit of wall area in a given time

6. Gases Collected by Water Displacement
Gases produced in the lab are often collected over water.
The gas produced by the reaction displaces the water, which is more dense, in the collected bottle.
A gas collected by the water is not pure but is always mixed with water vapor.
That is because water molecules are the liquid surface evaporate and mix with the gas.

7. Total pressure of Gas and Water Vapor
Water vapor exerts a pressure known as vapor pressure
To determine the total pressure of the gas and water vapor inside a collection bottle, you would raise the bottle until the water levels inside and outside the bottle were the same.
At that point, the total pressure inside the bottle would be the same as atmospheric pressure.

8. Calculate the Partial Pressure of the Dry Gas
Patm = Pgas + PH2O
Read the atmospheric pressure, Patm, form a barometer in the lab
Subtract eh water vapor pressure of the water at the given temperature form the total pressure.
The vapor pressure of water varies with temperature.
Look up the value of PH2O at the temperature on a standard reference table.

9. Example 1:
Oxygen gas from the decomposition of potassium chlorate, KClO3, was collected by water displacement. The barometric pressure and the temperature during the experiment were torr and 20 degrees C. What was the partial pressure of the oxygen collected?

10. Example 1: Given: Unknown PT = Patm + 731.0 torr
PH2O = 17.5 torr (look at table)
Patm=PO2 + PH2O
Unknown
PO2 in torr

11. Example 2:
A student has stored mL of neon gas over water on a day when the temperature is 27.0 degrees C. If the barometer in the room reads mmHg, what is the pressure of the neon gas in its container?