1. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Introductory Chemistry, Third Edition By Nivaldo J. Tro EXAMPLE 16.1 Identifying Oxidation and Reduction For each of the following reactions, identify the substance being oxidized and the substance being reduced. Solution : In this reaction, magnesium is gaining oxygen and losing electrons to oxygen. Mg is therefore oxidized and O 2 is reduced. In this reaction, a metal (Fe) is reacting with an electronegative nonmetal (Cl 2 ) Fe loses electrons and is therefore oxidized, while Cl 2 gains electrons and is therefore reduced. In this reaction, electrons are transferred from the Zn to the Fe 2+. Zn loses electrons and is oxidized. Fe 2+ gains electrons and is reduced.

2. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Introductory Chemistry, Third Edition By Nivaldo J. Tro EXAMPLE 16.1 Identifying Oxidation and Reduction Continued FOR MORE PRACTICE Example 16.11; Problems 35, 36, 37, 38. For each of the following reactions, identify the substance being oxidized and the substance being reduced. SKILLBUILDER 16.1 Identifying Oxidation and Reduction

3. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Introductory Chemistry, Third Edition By Nivaldo J. Tro EXAMPLE 16.2 Identifying Oxidizing and Reducing Agents FOR MORE PRACTICE Example 16.12; Problems 39, 40. Solution : In the previous example, we identified the substance being oxidized and reduced for these reactions. The substance being oxidized is the reducing agent, and the substance being reduced is the oxidizing agent. (a) Mg is oxidized and is therefore the reducing agent; O 2 is reduced and is therefore the oxidizing agent. (b) Fe is oxidized and is therefore the reducing agent; Cl 2 is reduced and is therefore the oxidizing agent. (c) Zn is oxidized and is therefore the reducing agent; Fe 2+ is reduced and is therefore the oxidizing agent. For each of the following reactions, identify the oxidizing agent and the reducing agent. SKILLBUILDER 16.2 Identifying Oxidizing and Reducing Agents

4. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Introductory Chemistry, Third Edition By Nivaldo J. Tro EXAMPLE 16.3 Assigning Oxidation States Since Br 2 is a free element, the oxidation state of both Br atoms is 0 (Rule 1). Solution: (a) Br 2 Br 0 Assign an oxidation state to each atom in each of the following. (a) Br 2 (b) K + (c) LiF (d) CO 2 (e) SO 4 2– (f) Na 2 O 2 (b) K + K + +1 Since K + is a monoatomic ion, the oxidation state of the K + ion is +1 (Rule 2). The oxidation state of Li is +1 (Rule 4). The oxidation state of F is –1 (Rule 5). Since this is a neutral compound, the sum of the oxidation states is 0 (Rule 3). (c) LiF Li F +1 –1 sum: +1 – 1 = 0

5. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Introductory Chemistry, Third Edition By Nivaldo J. Tro EXAMPLE 16.3 Assigning Oxidation States Continued The oxidation state of oxygen is –2 (Rule 5). The oxidation state of carbon must be deduced from Rule 3, which states that the sum of the oxidation states of all the atoms must be 0. Since there are two oxygen atoms, the oxidation state of O must be multiplied by 2 when computing the sum. (d) CO 2 (C ox state) + 2(O ox state) = 0 (C ox state) + 2(-2) = 0 (C ox state) - 4 = 0 C ox state = +4 C O 2 +4 –2 sum: +4 + 2(–2) = 0 The oxidation state of oxygen is –2 (Rule 5). The oxidation state of S is expected to be –2 (Rule 5). However, if that were the case, the sum of the oxidation states would not equal the charge of the ion. Since O is higher on the list, it takes priority, and the oxidation state of sulfur is computed by setting the sum of all of the oxidation states equal to –2 (the charge of the ion). (e) SO 4 2– (S ox state) + 4(O ox state) = –2 (S ox state) + 4(-2) = –2 (Oxygen takes priority over sulfur.) (S ox state) – 8 = –2 S ox state = –2 + 8 S ox state = +6 SO 4 2– +6 –2 sum: +6 + 4(-2) = –2

6. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Introductory Chemistry, Third Edition By Nivaldo J. Tro EXAMPLE 16.3 Assigning Oxidation States Continued The oxidation state of sodium is +1 (Rule 4). The oxidation state of O is expected to be –2 (Rule 5). However, Na takes priority, and we deduce the oxidation state of O by setting the sum of all of the oxidation states equal to 0. (f) Na 2 O 2 2(Na ox state) + 2(O ox state) = 0 2(+1) + 2(O ox state) = 0 (Sodium takes priority over oxygen.) O ox state = –1 Na 2 O 2 +1 –1 sum: 2(+1) + 2(–1) = 0 Assign an oxidation state to each atom in each of the following. (a) Zn (b) Cu 2+ (c) CaCl 2 (d) CF 4 (e) NO 2 - (f) SO 3 SKILLBUILDER 16.3 Assigning Oxidation States FOR MORE PRACTICE Example 16.13: Problems 47, 48, 49, 50, 51, 52, 53, 54, 55, 56.

7. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Introductory Chemistry, Third Edition By Nivaldo J. Tro EXAMPLE 16.4 Using Oxidation States to Identify Oxidation and Reduction FOR MORE PRACTICE Problems 59, 60, 61, 62. Use oxidation states to identify the element that is being oxidized and the element that is being reduced in the following redox reaction. Assign an oxidation state to each atom in the reaction. Since Ca increased in oxidation state, it was oxidized. Since H decreased in oxidation state, it was reduced. (Note that oxygen has the same oxidation state on both sides of the equation and was therefore neither oxidized nor reduced.) Solution : Use oxidation states to identify the element that is being oxidized and the element that is being reduced in the following redox reaction. SKILLBUILDER 16.4 Using Oxidation States to Identify Oxidation and Reduction

8. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Introductory Chemistry, Third Edition By Nivaldo J. Tro EXAMPLE 16.9 Predicting Spontaneous Redox Reactions Will the following redox reactions be spontaneous?

9. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Introductory Chemistry, Third Edition By Nivaldo J. Tro EXAMPLE 16.9 Predicting Spontaneous Redox Reactions Continued Will the following redox reactions be spontaneous? SKILLBUILDER 16.9 Predicting Spontaneous Redox Reactions FOR MORE PRACTICE Example 16.15; Problems 79, 80.

10. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Introductory Chemistry, Third Edition By Nivaldo J. Tro EXAMPLE 16.10 Predicting Whether a Metal Will Dissolve in Acid Will Cr dissolve in hydrochloric acid? FOR MORE PRACTICE Problems 85, 86. Will Ag dissolve in hydrobromic acid? SKILLBUILDER 16.10 Predicting Whether a Metal Will Dissolve in Acid Solution : Yes. Since Cr is above H 2 in the activity series, it will dissolve in HCl.

11. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Introductory Chemistry, Third Edition By Nivaldo J. Tro EXAMPLE 16.11 Identifying Oxidation and Reduction Determine the substance being oxidized and the substance being reduced in each of the following redox reactions. Solution: (a) Sn oxidized; O 2 reduced (b) Na oxidized; F 2 reduced (c) Mg oxidized; Cu 2+ reduced

12. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Introductory Chemistry, Third Edition By Nivaldo J. Tro EXAMPLE 16.12 Identifying Oxidizing Agents and Reducing Agents Solution : (a) Sn is the reducing agent; O 2 is the oxidizing agent. (b) Na is the reducing agent; F 2 is the oxidizing agent. (c) Mg is the reducing agent; Cu 2+ is the oxidizing agent. Identify the oxidizing and reducing agents in each of the following redox reactions.

13. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Introductory Chemistry, Third Edition By Nivaldo J. Tro EXAMPLE 16.13 Assigning Oxidation States Assign an oxidation state to each atom in each of the following compounds. (a) Al (b) Al 3+ (c) N 2 O (d) CO 3 2– Solution :

14. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Introductory Chemistry, Third Edition By Nivaldo J. Tro EXAMPLE 16.15 Predicting Spontaneous Redox Reactions Predict whether each of the following redox reactions will be spontaneous. Solution : (a) Spontaneous (b) Nonspontaneous