Copyright©2000 by Houghton Mifflin Company. All rights reserved. 1 Chemistry FIFTH EDITION by Steven S. Zumdahl University of Illinois

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 2 Chemistry FIFTH EDITION Chapter 4 Types of Chemical Reactions and Solution Stoichiometry Don’t forget Homework!!!!

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 3 Section 4.9 Oxidation – Reduction Reactions Reactions in which one or more electrons are transferred. Also called Redox Reactions Oxidation States (Oxidation Numbers): Arbitrary numbers assigned to atoms to provide a way to keep track of electrons in redox rxns.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 4 Rules for Assigning Oxidation States (p 156) 1. Oxidation state of an atom in an element = 0 2. Oxidation state of monatomic ion = charge 3. Oxygen =  2 in covalent compounds (except in peroxides where it =  1) 4. H = +1 in covalent compounds 5. Fluorine =  1 in compounds 6. Sum of oxidation states = 0 in compounds Sum of oxidation states = charge of the ion

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 5 Possibility exists for non-integer oxidation numbers. Example: Fe 3 O 4 O.N. of O = -2, therefore each of the 3 Fe has O.N. of +8/3

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 6 Oxidation – Reduction Reactions Transfer of Electrons OXIDATION: Loss of electrons Increase in oxidation number REDUCTION: Gain of electrons Decrease in oxidation number.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 7 OIL RIG Oxidation Involves Loss Reduction Involves Gain LEO say GER Loss of Electrons  Oxidation Gain of Electrons  Reduction

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 8 Oxidizing Agent: Reagent responsible for oxidizing. In the process, it is reduced. Is an electron acceptor. Reducing Agent: Reagent responsible for reducing. In the process, it is oxidized. Is an electron donor.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 9 CH 4 (g) + 2 O 2 (g)  CO 2 (g) + 2 H 2 O (g) What is reduced? What is oxidized? What is the oxidizing agent? What is the reducing agent? Let’s do a problem.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 10 Figure 4.19 A Summary of an Oxidation- Reduction Process

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 11 Balancing by Half-Reaction Method (in acidic solution) 1.Write separate reduction, oxidation reactions. 2.For each half-reaction:  Balance elements (except H, O)  Balance O using H 2 O  Balance H using H +  Balance charge using electrons

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 12 Balancing by Half-Reaction Method (continued) 3.If necessary, multiply by integer to equalize electron count. 4.Add half-reactions. 5.Check that elements and charges are balanced. Let’s do 64 a, d.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 13 Half-Reaction Method – Balancing in Base 1.Balance as in acid. 2.Add OH  that equals H + ions (both sides!) 3.Form water by combining H +, OH . 4.Check elements and charges for balance. Let’s do some problems.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 14 Don’t forget your Homework!!