1. Balancing RedOx Equations G&D TEXT 9.2, Chang Chapter 19 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2. Balancing Redox Equations 19.1 1.Write the unbalanced equation for the reaction in ionic form. The oxidation of Fe 2+ to Fe 3+ by Cr 2 O 7 2- in acid solution? 2.Separate the equation into two half-reactions. Oxidation: Reduction: 3.Balance the atoms other than O and H in each half-reaction.

3. Balancing Redox Equations 4.For reactions in acid, add H 2 O to balance O atoms and H + to balance H atoms. 5.Add electrons to one side of each half-reaction to balance the charges on the half-reaction. 6.If necessary, equalize the number of electrons in the two half- reactions by multiplying the half-reactions by appropriate coefficients. 19.1

4. Balancing Redox Equations 7.Add the two half-reactions together and balance the final equation by inspection. The number of electrons on both sides must cancel. Oxidation: Reduction: 8.Verify that the number of atoms and the charges are balanced. 19.1 9.For reactions in basic solutions, add OH - to both sides of the equation for every H + that appears in the final equation.

5. Summary - How to Balance REDOX Equations 1.Write the unbalanced equation for the reaction in ionic form. 2.Separate the equation into two half-reactions. 3.Balance the atoms other than O and H in each half-reaction. 4.For reactions in acid, add H2O to balance O atoms and H+ to balance H atoms. 5.Add electrons to one side of each half-reaction to balance the charges on the half-reaction. 6.If necessary, equalize the number of electrons in the two half- reactions by multiplying the half-reactions by appropriate coefficients. 7.Add the two half-reactions together and balance the final equation by inspection. The number of electrons on both sides must cancel. 8.Verify that the number of atoms and the charges are balanced. 9.For reactions in basic solutions, add OH- to both sides of the equation for every H+ that appears in the final equation.

6. Try balancing these equations: T1: magnesium reduces lead ions to lead metal T2: sulfur dioxide is oxidized to sulfate, iodine is reduced to iodide ions (assume acidic solution) T3: hydrogen peroxide oxidizes iron(II) to iron(III) in acidic solution T4: zinc reduces acidified dichromate ions to chromium(III) T5: acidified permanganate ions oxidize methanol to carbon dioxide and water T6: chlorate ion (ClO 3 - ) is oxidized to the perchlorate ion (ClO 4 - ) and is reduced to the chloride ion