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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 O2 is reduced. In this reaction, a metal (Fe) is reacting with an electronegative nonmetal (Cl 2) Fe loses electrons and is therefore oxidized, while Cl2 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. Fe2+ gains electrons and is reduced. Introductory Chemistry, Third Edition By Nivaldo J. Tro Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. EXAMPLE 16.1 Identifying Oxidation and Reduction Continued SKILLBUILDER 16.1 Identifying Oxidation and Reduction For each of the following reactions, identify the substance being oxidized and the substance being reduced. FOR MORE PRACTICE Introductory Chemistry, Third Edition By Nivaldo J. Tro Example 16.11; Problems 35, 36, 37, 38. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. EXAMPLE 16.2 Identifying Oxidizing and Reducing Agents For each of the following reactions, identify the oxidizing agent and the reducing agent. 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; O2 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. SKILLBUILDER 16.2 Identifying Oxidizing and Reducing Agents For each of the following reactions, identify the oxidizing agent and the reducing agent. FOR MORE PRACTICE Introductory Chemistry, Third Edition By Nivaldo J. Tro Example 16.12; Problems 39, 40. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. EXAMPLE 16.3 Assigning Oxidation States Assign an oxidation state to each atom in each of the following. (a) Br2 (b) K+ (c) LiF (d) CO2 (e) SO42– (f) Na2O2 Since Br2 is a free element, the oxidation state of both Br atoms is 0 (Rule 1). Solution: (a) Br2 Br Br 0 0 Since K+ is a monoatomic ion, the oxidation state of the K+ ion is +1 (Rule 2). (b) K+ K+ +1 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 Introductory Chemistry, Third Edition By Nivaldo J. Tro Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. 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) CO2 (C ox state) + 2(O ox state) = 0 (C ox state) + 2(-2) = 0 (C ox state) - 4 = 0 C ox state = +4 C O2 +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) SO42– (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 S O42– +6 –2 sum: +6 + 4(-2) = –2 Introductory Chemistry, Third Edition By Nivaldo J. Tro Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. 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. SKILLBUILDER 16.3 (f) Na2O2 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 Na2 O2 +1 –1 sum: 2(+1) + 2(–1) = 0 Assigning Oxidation States Assign an oxidation state to each atom in each of the following. (a) Zn (b) Cu2+ (c) CaCl2 (d) CF4 (e) NO2(f) SO3 FOR MORE PRACTICE Introductory Chemistry, Third Edition By Nivaldo J. Tro Example 16.13: Problems 47, 48, 49, 50, 51, 52, 53, 54, 55, 56. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. EXAMPLE 16.4 Using Oxidation States to Identify Oxidation and Reduction 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: SKILLBUILDER 16.4 Using Oxidation States to Identify Oxidation and Reduction Use oxidation states to identify the element that is being oxidized and the element that is being reduced in the following redox reaction. FOR MORE PRACTICE Introductory Chemistry, Third Edition By Nivaldo J. Tro Problems 59, 60, 61, 62. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. EXAMPLE 16.9 Predicting Spontaneous Redox Reactions Will the following redox reactions be spontaneous? Introductory Chemistry, Third Edition By Nivaldo J. Tro Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. EXAMPLE 16.9 Predicting Spontaneous Redox Reactions Continued SKILLBUILDER 16.9 Predicting Spontaneous Redox Reactions Will the following redox reactions be spontaneous? FOR MORE PRACTICE Introductory Chemistry, Third Edition By Nivaldo J. Tro Example 16.15; Problems 79, 80. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. EXAMPLE 16.10 Predicting Whether a Metal Will Dissolve in Acid Will Cr dissolve in hydrochloric acid? Solution: Yes. Since Cr is above H2 in the activity series, it will dissolve in HCl. SKILLBUILDER 16.10 Predicting Whether a Metal Will Dissolve in Acid Will Ag dissolve in hydrobromic acid? FOR MORE PRACTICE Introductory Chemistry, Third Edition By Nivaldo J. Tro Problems 85, 86. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. 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; O2 reduced (b) Na oxidized; F2 reduced (c) Mg oxidized; Cu2+ reduced Introductory Chemistry, Third Edition By Nivaldo J. Tro Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. EXAMPLE 16.12 Identifying Oxidizing Agents and Reducing Agents Identify the oxidizing and reducing agents in each of the following redox reactions. Solution: (a) Sn is the reducing agent; O2 is the oxidizing agent. (b) Na is the reducing agent; F2 is the oxidizing agent. (c) Mg is the reducing agent; Cu2+ is the oxidizing agent. Introductory Chemistry, Third Edition By Nivaldo J. Tro Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. EXAMPLE 16.13 Assigning Oxidation States Assign an oxidation state to each atom in each of the following compounds. (a) Al (b) Al3+ (c) N2O (d) CO32– Solution: Introductory Chemistry, Third Edition By Nivaldo J. Tro Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. EXAMPLE 16.15 Predicting Spontaneous Redox Reactions Predict whether each of the following redox reactions will be spontaneous. Solution: (a) Spontaneous (b) Nonspontaneous Introductory Chemistry, Third Edition By Nivaldo J. Tro Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved.