1 Chapter 11 Gases Partial Pressure (Dalton’s Law) Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

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

3 Dalton’s Law of Partial Pressures states that the total pressure Depends on the total number of gas particles, not on the types of particles. Exerted by a gas mixture is the sum of the partial pressures of those gases. P T = P 1 + P Dalton’s Law of Partial Pressures

4 Illustrating Partial Pressures Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

5 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 STP = 22.4 L Gas mixtures Total Pressure 0.5 mol O mol He 0.2 mol Ar 1.0 mol 1.0 mol N mol O mol He 1.0 mol 1.0 atm

6 Scuba Diving When a scuba diver makes a deep dive, the increased pressure causes N 2 (g) to dissolve in the blood. If the rise is too fast, the dissolved N 2 forms bubbles in the blood, a dangerous condition called "the bends". Helium is mixed with O 2 to prepare breathing mixtures for deep descents. Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

7 Learning Check A scuba tank contains O 2 with a pressure of atm and He at 855 mm Hg. What is the total pressure in mm Hg in the tank? Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

8 1. Convert the pressure in atm to mm Hg atm x 760 mm Hg = 342 mm Hg = P O 2 1 atm 2. Calculate the sum of the partial pressures. P total = PO 2 + P He P total = 342 mm Hg mm Hg = 1197 mm Hg Solution

9 For a deep dive, some scuba divers are using a mixture of helium and oxygen gases with a pressure of 8.00 atm. If the oxygen has a partial pressure of 1280 mm Hg, what is the partial pressure of the helium? 1) 520 mm Hg 2) 2040 mm Hg 3) 4800 mm Hg Learning Check

10 3) 4800 mm Hg P Total = 8.00 atm x 760 mm Hg = 6080 mm Hg 1 atm P Total = P O + P He 2 P He = P Total - P O 2 P He = 6080 mm Hg mm Hg = 4800 mm Hg Solution

11 Gases Collected Over Water A gas produced in the laboratory Usually contains water vapor. P T = P water + P gas Has a partial pressure obtained by subtracting the vapor pressure of water from the P T. Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

12 Learning Check The decomposition of KClO 3 produces O 2 gas and solid KCl. If 124 mL of O 2 is collected over water at 762 mm Hg and 20.0  C, how many moles of O 2 were produced? 2KClO 3 (s) 2KCl(s) + 3O 2 (g)

13 Solution Partial pressure water at 20.0  C = 18 mm Hg P T = P water + P gas 762 mm Hg = 18 mm Hg + PO 2 PO 2 = 762 mm Hg - 18 mm Hg = 744 mm Hg PV = nRT n = PV = (744 mm Hg)(0.124 L) = mol O 2 RT (62.4 L mm Hg)(293 K) mol K

14 Gases We Breathe The air we breathe Is a gas mixture. Contains mostly N 2 and O 2 and small amounts of other gases. Table 11.7 Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

15 A.If the atmospheric pressure today is 745 mm Hg, what is the partial pressure (mm Hg) of O 2 in the air? 1) ) 156 3) 760 B. At an atmospheric pressure of 714, what is the partial pressure (mm Hg) N 2 in the air? 1) 557 2) 9.143) Learning Check

16 A. If the atmospheric pressure today is 745 mm Hg, what is the partial pressure (mm Hg) of O 2 in the air? 2) 156 B. At an atmospheric pressure of 714, what is the partial pressure (mm Hg) N 2 in the air? 1) 557 Solution

17 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 release CO 2 into the blood. Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

18 Blood Gases In the body, Cells use up O 2 and give off CO 2. O 2 flows into the tissues because the partial pressure of O 2 is higher (100 mm Hg) in oxygenated blood, and lower (<30 mm Hg) in the tissues. CO 2 flows out of the tissues because the partial pressure of CO 2 is higher (>50 mm Hg) in the tissues, and lower (40 mm Hg) in the blood.

19 Gas Exchange During Breathing Table 11.8 Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings