1. Page 79 and 81 of INB

2. Essential question: Why must scientist’s account for water vapor when they collect gases by water displacement?

3. Pressure: Force (F) = mass x acceleration. Or F=ma Pressure: force per unit area on a surface. Or P=F/Area Dancer and Ice

4. Measuring pressure: Barometer is used to measure atmospheric pressure. Atmospheric pressure at sea level is 760 mm Hg. Monometer is used to measure pressure of an enclosed gas.

5. The difference in mercury levels is the pressure exerted by the gas.

6. UNITS of Pressure 1 atm = 760 mm Hg = 760 Torr = 101.325 Kpa = 14.700 psi 1 Pa = 1 N acting on 1 m 2 STP = Standard temperature and pressure = 1 atmosphere at 0 o C

7. Conversions: The average pressure in Denver is 0.830 atm. How much pressure is that in mm Hg, and Kpa?

8. Daltons Law of partial pressure Total pressure of a gas mixture is the sum of all the partial pressures of the component gases. # of gases present does not effect total pressure, just # of particles. Partial pressure: the pressure of each gas in a mixture. Pressure depends on the chance of particles hitting the wall of the container.

9. Gases collected by water displacement: Many experiments will have a gas collected by water displacement. Some water vapor will be in the collected gas Use Dalton’s law of partial pressure to calculate amount of gas collected by subtracting the amount of water particles.

11. Example Oxygen gas is collected from the decomposition of KCLO 3, by water displacement. The barometer pressure was 731 torr and the temperature was 20.0 o C. What is the partial pressure of O 2 ?