© 2013 Pearson Education, Inc. Chapter 7, Section 9 General, Organic, and Biological Chemistry Fourth Edition Karen Timberlake 7.9 Partial Pressures (Dalton’s Law) Chapter 7 Gases © 2013 Pearson Education, Inc. Lectures

© 2013 Pearson Education, Inc. Chapter 7, Section 9 In a gas mixture, each gas exerts its partial pressure, which is the pressure it would exert if it were the only gas in the container. Dalton’s law states that the total pressure of a gas mixture is the sum of the partial pressures of the gases in the mixture. Partial Pressure, Dalton’s Law 2

© 2013 Pearson Education, Inc. Chapter 7, Section 9 Dalton’s Law of Partial Pressures indicates that pressure depends on the total number of gas particles. Dalton’s Law of Partial Pressures 3

© 2013 Pearson Education, Inc. Chapter 7, Section 9 For example, at STP, one mole of a pure gas will exert the same pressure as one mole of a gas mixture in a 22.4 L container. V = 22.4 L Gas mixtures Total Pressure 0.5 mole O mole He 0.2 mole Ar 1.0 mole 1.0 mole N mole O mole He 1.0 mole 1.0 atm 4

© 2013 Pearson Education, Inc. Chapter 7, Section 9 Composition of Air Air is a mixture of gases, including nitrogen, oxygen, carbon dioxide, argon, and water gases. 5

© 2013 Pearson Education, Inc. Chapter 7, Section 9 Guide to Solving for Partial Pressure 6

© 2013 Pearson Education, Inc. Chapter 7, Section 9 Learning Check A scuba tank contains a mixture of He and O 2 gases at 7.00 atm. If the pressure of O 2 gas is 1140 mmHg, what is the partial pressure of He gas in the tank? 7

© 2013 Pearson Education, Inc. Chapter 7, Section 9 A scuba tank contains a mixture of He and O 2 gases at 7.00 atm. If the pressure of O 2 gas is 1140 mmHg, what is the partial pressure of He gas in the tank? Step 1 Write the equation for partial pressures. Step 2 Rearrange the equation to solve for the unknown pressure. Solution 8

© 2013 Pearson Education, Inc. Chapter 7, Section 9 A scuba tank contains a mixture of He and O 2 gases at 7.00 atm. If the pressure of O 2 gas is 1140 mmHg, what is the partial pressure of He gas in the tank? Step 3 Substitute known pressures into the equation and calculate the unknown partial pressure. Solution 9

© 2013 Pearson Education, Inc. Chapter 7, Section 9 Blood Gases  In the lungs, O 2 enters the blood, at the same time that CO 2 is released.  In the tissues, O 2 enters the cells, which release CO 2 into the blood. 10

© 2013 Pearson Education, Inc. Chapter 7, Section 9 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 the blood. Partial Pressures (mmHg) in Blood and Tissue Gas Oxygenated Deoxygenated Tissues Blood Blood O mmHg 40 mmHg 30 mmHg or less CO 2 40 mmHg 46 mmHg 50 mmHg or greater 11

© 2013 Pearson Education, Inc. Chapter 7, Section 9 Changes in Partial Pressures of Blood Gases During Breathing 12