General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 1 Chapter 7 Gases 7.9 Partial Pressure (Dalton’s Law)

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 2 The partial pressure of a gas  is the pressure of each gas in a mixture  is the pressure that gas would exert if it were by itself in the container Partial Pressure

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 3 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 Dalton’s Law of Partial Pressures

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 4 Dalton’s Law of Partial Pressures (continued)

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 5  For example, at STP, one mole of a pure gas in a volume of 22.4 L will exert the same pressure as one mole of a gas mixture in 22.4 L. 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

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 6 Scuba Diving  When a scuba diver is below the ocean surface, the increased pressure causes more N 2 (g) to dissolve in the blood.  If a diver rises too fast, the dissolved N 2 gas can form bubbles in the blood, a dangerous and painful condition called “the bends.”  For deep descents, helium, which does not dissolve in the blood, is added to O 2.

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. Guide to Solving for Partial Pressure 7

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 8 Learning Check A scuba tank contains O 2 with a pressure of atm and He at 855 mmHg. What is the total pressure in mmHg in the tank?

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 9 STEP 1 Write the equation for partial pressures. P total = P O 2 + P He atm x 760 mmHg = 342 mmHg = P O 2 1 atm STEP 2 Solve for the unknown P total = P O 2 + P He STEP 3 Substitute data and calculate P total = 342 mmHg mmHg = 1197 mmHg Solution

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 10 For a deep descent, a scuba diver uses a mixture of helium and oxygen with a total pressure of 8.00 atm. If the oxygen has a partial pressure of 1280 mmHg, what is the partial pressure of the helium? 1) 520 mmHg 2) 2040 mmHg 3) 4800 mm Hg Learning Check

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 11 3) 4800 mmHg STEP 1 Write the equation for the sum of partial pressures. P Total = P O 2 + P He P Total = 8.00 atm x 760 mmHg = 6080 mmHg 1 atm STEP 2 Solve for the unknown partial pressure. P He = P Total – P O 2 STEP 3 Substitute pressures and calculate unknown. P He = 6080 mmHg – 1280 mmHg = 4800 mmHg Solution

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 12 Gases We Breathe The air we breathe  is a gas mixture  contains mostly N 2 and O 2 and small amounts of other gases

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 13 A. If the atmospheric pressure today is 745 mmHg, what is the partial pressure (mmHg) of O 2 in the air? 1) 35.6 mmHg 2) 156 mmHg 3) 760 mmHg B. At an atmospheric pressure of 714 mmHg, what is the partial pressure (mmHg) of N 2 in the air? 1) 557 mmHg 2) 9.14 mmHg 3) mmHg Learning Check

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 14 A. If the atmospheric pressure today is 745 mmHg, what is the partial pressure (mmHg) of O 2 in the air? 2) 156 mmHg 745 mmHg (total) x 21 mmHg O 2 = 156 mmHg 100 mmHg (total) B. At an atmospheric pressure of 714 mmHg, what is the partial pressure (mmHg) N 2 in the air? 1) 557 mmHg 714 mmHg (total) x 78 mmHg N 2 = 557 mmHg of N mmHg (total) Solution

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 15 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.

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 16 Blood Gases (continued) 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 Blood Deoxygenated Blood Tissues O mmHg 40 mmHg 30 mmHg or less CO 2 40 mmHg 46 mmHg 50 mmHg or greater

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 17 Changes in Partial Pressures of Blood Gases During Breathing