1. © 2014 Pearson Education, Inc. Chapter 11 Gases 11.10 Partial Pressures Learning Goal Use Dalton’s Law of partial pressures to calculate the total pressure of a mixture of gases. Chapter 11 Lecture Basic Chemistry Fourth Edition

2. © 2014 Pearson Education, Inc. 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. © 2014 Pearson Education, Inc. 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 2 + P 3..... Total pressure of the gas mixture = Sum of the partial pressures of the gases in the mixture Partial Pressure

4. © 2014 Pearson Education, Inc. Total Pressure Equal Sum of Partial Pressures The total pressure of two gases is the sum of their partial pressures.

5. © 2014 Pearson Education, Inc. The air you breathe is a mixture of gases. A typical mixture of gases in the air includes: N 2, O 2, CO 2, Ar, and H 2 O. Air, Mixture of Gases

6. © 2014 Pearson Education, Inc. Air, Mixture of Gases

7. © 2014 Pearson Education, Inc. 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? Learning Check

8. © 2014 Pearson Education, Inc. 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 partial pressures. Solution

9. © 2014 Pearson Education, Inc. 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 2 Rearrange the equation to solve for the unknown pressure. Solution

10. © 2014 Pearson Education, Inc. 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 3 Substitute known pressures into the equation and calculate the unknown pressure. Solution

11. © 2014 Pearson Education, Inc. 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 Collecting Gas over Water

12. © 2014 Pearson Education, Inc. Magnesium (Mg) reacts with HCl, to produce H 2 gas. Mg(s) + 2HCl(aq)  MgCl 2 (aq) + H 2 (g) As the H 2 gas is produced, it displaces some of the water in the container. The gas collected will be a mixture of H 2 and water vapor. Collecting Gas over Water

13. © 2014 Pearson Education, Inc. We use the vapor pressure of water at the experimental temperature to determine the amount of dry H 2 gas produced in the reaction. Collecting Gas over Water Figure 11.9 A gas from a reaction is collected by bubbling through water. Due to evaporation of water, the total pressure is equal to the partial pressure of the gas and the vapor pressure of water.

14. © 2014 Pearson Education, Inc. Guide, Collecting Gas over Water

15. © 2014 Pearson Education, Inc. When magnesium reacts with HCl, a volume of 0.355 L of H 2 gas is collected over water at 26 °C. The vapor pressure of water at 26 °C is 25 mmHg. If the total pressure is 752 mmHg, how many moles of H 2 gas were collected? Mg(s) + 2HCl(aq)  MgCl 2 (aq) + H 2 (g) Learning Check

16. © 2014 Pearson Education, Inc. In the following reaction 0.355 L sample of H 2 gas is collected over water at 26 °C. If the total pressure is 752 mmHg, how many moles of H 2 gas were collected? Mg(s) + 2HCl(aq)  MgCl 2 (aq) + H 2 (g) Step 1 Obtain the vapor pressure of water. The vapor pressure of water at 26 °C is 25 mmHg. Solution

17. © 2014 Pearson Education, Inc. In the following reaction 0.355 L sample of H 2 gas is collected over water at 26 °C. If the total pressure is 752 mmHg, how many moles of H 2 gas were collected? Mg(s) + 2HCl(aq)  MgCl 2 (aq) + H 2 (g) Step 2 Subtract the vapor pressure from the total P of the gas mixture to give the partial pressure of needed gas. Solution

18. © 2014 Pearson Education, Inc. In the following reaction 0.355 L sample of H 2 gas is collected over water at 26 °C. If the total pressure is 752 mmHg, how many moles of H 2 gas were collected? Mg(s) + 2HCl(aq)  MgCl 2 (aq) + H 2 (g) Step 3 Use the ideal gas law to convert P gas to moles or grams of gas collected. Solution

19. © 2014 Pearson Education, Inc. Step 3 Use the ideal gas law to convert P gas to moles or grams of gas collected. Solve for moles of H 2 gas by placing the partial pressure of H 2 (727 mmHg), volume of gas container (0.355 L), temperature (26 °C + 273 = 299 K), and R, using mmHg into the ideal gas equation. Solution

20. © 2014 Pearson Education, Inc. During breathing, an exchange of gases occurs in which oxygen from the air diffuses into the lungs and into the blood carbon dioxide produced in the cells is carried to the lungs to be exhaled Chemistry Link to Health

21. © 2014 Pearson Education, Inc. In Table 11.8, partial pressures are given for the gases in air that we inhale (inspired air), air in the alveoli, and air that we exhale (expired air). The partial pressure of water vapor increases within the lungs because the vapor pressure of water is 47 mmHg at body temperature. Chemistry Link to Health

22. © 2014 Pearson Education, Inc. Chemistry Link to Health

23. © 2014 Pearson Education, Inc. Chemistry Link to Health

24. © 2014 Pearson Education, Inc. Concept Map