1. Gases Online Lecture Part 2

2. Gas Density and Molar Mass Using the ideal gas law and the density of a gas you can solve for the molar mass of the gas. (Reverse it too!) Molar Mass = dRT P Ex – The density of a gas was measured at 1.50 atm and 27°C and found to be 1.95 g/L. Calculate the molar mass of the gas.

3. Using the drt equation!

4. Dalton’s Law of Partial Pressures For a _________ of gases in a container, the total pressure exerted is the ____ of the pressures that each gas would exert if it were alone R, T and V will be the same in each problem b/c the gases are in the same tank P total = P 1 + P 2 + P 3 + etc (P 1,P 2, and P 3 are partial pressures of individual gases) Substitute in the Ideal Gas Law

5. Dalton’s Example Mixtures of helium and oxygen are used in scuba diving tanks to help prevent “the bends”. For a particular dive, 46 L He at 25°C and 1.0 atm and 12 L O 2 at 25°C and 1.0 atm were pumped into a tank with a volume of 5.0 L. Calculate the partial pressure of each gas and the total pressure in the tank at 25°C.

7. Mole Fraction ______of the number of ______ of a given component in a mixture to the _______ number of moles in the mixture  – chi, represents the _____________ » No unit  1 = n 1  1 = P 1 n total P total Could use this to solve for , partial pressure or P total.

8. Mole Fraction Examples Ex #1 – The partial pressure of oxygen was observed to be 156 torr in air with a total atmospheric pressure of 743 torr. Calculate the mole fraction of O 2 present. Ex #2 – The mole fraction of nitrogen in the air is 0.7808. Calculate the partial pressure of N 2 in air when the atmospheric pressure is 760. torr.

10. Vapor Pressure of H 2 O When gas is collected by H 2 O displacement, a mixture of gases results (the _______ gas and the __________) H 2 O vapor __________ from the surface of the H 2 O and _______ above the liquid, while some H 2 O vapor also __________ to the liquid When _________________, the vapor pressure will be constant The vapor pressure of the water depends on the temperature, typically this information will be given to you in the problem or you may have to look it up.

11. Gas Collection of Water Ex. A sample of solid potassium chlorate was heated in a test tube and decomposed into potassium chloride and oxygen. The oxygen produced was collected by displacement of water at 22°C at a total pressure of 754 torr. The volume of the gas collected was 0.650 L and the vapor pressure of water at 22°C is 21 torr. Calculate the partial pressure of O 2 in the gas collected and the mass of KClO 3 that was decomposed.