1. Chemistry An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Chapter 6 Gases 6.8 Partial Pressure Dalton’s Law 1

2. Chemistry An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Partial Pressure The partial pressure of a gas is the pressure that each gas in a mixture would exert if it were by itself in the container. 2

3. Chemistry An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Dalton’s Law of Partial Pressures Dalton’s law of partial pressures indicates that pressure depends on the total number of gas particles, not on the types of particles the total pressure exerted by gases in a mixture is the sum of the partial pressures of those gases P T = P 1 + P 2 + P 3 +.... 3

4. Chemistry An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Total Pressure For example, at STP, 1 mole of a pure gas in a volume of 22.4 L will exert the same pressure as 1 mole of a gas mixture in 22.4 L. Gas mixtures 4 1.0 mole N 2 0.4 mole O 2 0.6 mole He 1.0 mole 0.5 mole O 2 0.3 mole He 0.2 mole Ar 1.0 mole 1.0 atm

5. Chemistry An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Scuba Diving When a scuba diver dives, the increased pressure causes N 2 (g) to dissolve in the blood. If a diver rises too fast, the dissolved N 2 will form bubbles in the blood, a dangerous and painful condition called “the bends.” Helium, which does not dissolve in the blood, is mixed with O 2 to prepare breathing mixtures for deep descents. 5

6. Chemistry An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Air is a Gas Mixture The air we breathe is a gas mixture contains mostly N 2 and O 2, and small amounts of other gases 6

7. Chemistry An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Guide to Solving for Partial Pressure 7

8. Chemistry An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Guide to Solving for Partial Pressure A scuba tank contains O 2 with a pressure of 0.450 atm and He at 855 mmHg. What is the total pressure in mmHg in the tank? Step 1 Write the equation for the sum of the partial pressures. P total = P O2 + P He Step 2 Solve for the unknown pressure. P total = P O2 + P He Convert the pressure in atm to mmHg. 0.450 atm  760 mmHg = 342 mmHg = P O2 1 atm 8

9. Chemistry An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Guide to Solving for Partial Pressure Step 3 Substitute known pressures and calculate the unknown partial pressure. P total = P O2 + P He P total = 342 mmHg + 855 mmHg = 1197 mmHg 9

10. Chemistry An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Learning Check For a deep dive, a scuba diver uses a mixture of helium and oxygen with a pressure of 8.00 atm. If the oxygen has a partial pressure of 1280 mmHg, what is the partial pressure of the helium? A. 520 mmHg B. 2040 mmHg C. 4800 mmHg 10

11. Chemistry An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Solution For a deep dive, a scuba diver uses a mixture of helium and oxygen with a pressure of 8.00 atm. If the oxygen has a partial pressure of 1280 mmHg, what is the partial pressure of the helium? Step 1 Write the equation for the sum of the partial pressures. P total = P O2 + P He Step 2 Solve for the unknown pressure. P He = P total − P O2 Convert the pressure in atm to mmHg. P total = 8.00 atm  760 mmHg = 6080 mmHg 1 atm 11

12. Chemistry An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Solution For a deep dive, a scuba diver uses a mixture of helium and oxygen with a pressure of 8.00 atm. If the oxygen has a partial pressure of 1280 mmHg, what is the partial pressure of the helium? Step 3 Substitute known pressures and calculate the unknown partial pressure. P He = 6080 mmHg – 1280 mmHg = 4800 mmHg The answer is C, 4800 mm Hg. 12

13. Chemistry An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Blood Gases In the lungs, O 2 enters the blood, while CO 2 from the blood is released. In the tissues, O 2 enters the cells, which releases CO 2 into the blood. 13

14. Chemistry An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Blood Gases In the body, O 2 flows into the tissues because the partial pressure of O 2 is higher in blood and lower in the tissues CO 2 flows out of the tissues because the partial pressure of CO 2 is higher in the tissues and lower in blood 14

15. Chemistry An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Partial Pressures in Blood Partial Pressures in Blood and Tissue 15 GasOxygenated Blood Deoxygenated Blood Tissues O 2 1004030 or less CO 2 404650 or greater

16. Chemistry An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Gas Exchange During Breathing 16

17. Chemistry An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Gas Law Concepts 17