1. More Gas Laws and Concepts

2. Measuring Pressure with a Barometer

3. Measuring Pressure of a Gas A Manometer is a device to measure the pressure of an enclosed gas sample. A common simple manometer consists of a U shaped tube of glass filled with some liquid. Typically the liquid is mercury because of its high density. What does one look like?

4. Closed Manometer Whatever the height difference is, that is your pressure in mmHg

5. Gas pressure = atmospheric pressure – h. Open Manometer

6. Gas pressure = atmospheric pressure + h. Open Manometer

7. Manometer Practice 25mm Atmospheric Pressure = 757.8mmHg

8. Dalton’s Law of Partial Pressures 1)the total pressure exerted by a mixture of gases is the sum of the individual pressures of each gas and 2)each individual gas behaves as if it were independent of the others. For example, if two gases such as oxygen and nitrogen are present in a flask, and P Nitrogen =590 mm Hg P Oxygen = 160 mm Hg, the total pressure is 750 mm Hg. Mathematically, this means: P total = P 1 + P 2 + P 3 + …

9. = + + + Dalton’s Law of Partial Pressures & Air Pressure P O2O2 P N2N2 P CO 2 P Ar EARTH P O2O2 P N2N2 P CO 2 P Ar P Total 149 590 3 8 mm Hg P Total = + + + 149 mm Hg 590 mm Hg 3 mm Hg 8 mm Hg P Total = 750 mm Hg

10. Dalton’s Law of Partial Pressures Hydrogen gas is bubbled through water to a pressure of 756mmHg at 30.0°C. The water vapor pressure at 30.0°C is 31.9mmHg. What is the pressure of dry hydrogen? P total = P 1 + P 2 + P 3 + …

11. Table of Partial Pressures of Water Vapor Pressure of Water Temperature Pressure ( o C) (kPa) 0 0.6 5 0.9 8 1.1 10 1.2 12 1.4 14 1.6 16 1.8 18 2.1 20 2.3 ( o C) (kPa) 21 2.5 22 2.6 23 2.8 24 3.0 25 3.2 26 3.4 27 3.6 28 3.8 29 4.0 ( o C) (kPa) 30 4.2 35 5.6 40 7.4 50 12.3 60 19.9 70 31.2 80 47.3 90 70.1 100 101.3

12. Mole Fraction The ratio of the number of moles of a given component in a mixture to the total number of moles in the mixture. 

13. The partial pressure of oxygen was observed to be 156 torr in air with total atmospheric pressure of 743 torr. Calculate the mole fraction of O 2 present.

14. 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. 0.7808 X 760. torr = 593 torr

15. Reaction of Mg with HCl SimulationSimulation – JAVA applet by Mr. Fletcher (CHEMFILES.COM)

16. Ideal Gas Law Lab Involves stoichiometry, AND Dalton’s Law, AND finally PV=nRT Can We do an example problem? sure Starting with 0.314g of Mg ribbon and excess hydrochloric acid (HCl), 35.5mL of hydrogen gas is made and collected over water that is 24.3°C at 0.999atm, along with some magnesium chloride. With this data, calculate the value of R to 3 sig figs, with units of atmL/molK.

17. Sample Problem Starting with 0.314g of Mg ribbon and excess hydrochloric acid (HCl), 35.5mL of hydrogen gas is made and collected over water that is 24.3°C at 0.999atm, along with some magnesium chloride. With this data, calculate the value of R to 3 sig figs, with units of atmL/molK. So in asking for R, I am asking you to solve PV=nRT. A quick glance at my inventory shows me that: P=0.999atm…but there’s a trick to that involving Dalton’s Law V=35.5mL, thanks to the eudiometer, be sure to convert to liters n= we can stoichiometry to convert 0.314g of Mg to moles of H 2 R is my unknown T=24.3°C..which of course is 297K