2.6 Redox Part 1a. Balancing Redox Reactions (Half-equation method) b. write ionic half-equations and use them to construct full ionic equations. Connector: Updated_Crowe_2012

Balancing Redox Reactions (Half-equation method) The half-equation method separates a redox reaction into its oxidation and reduction half reactions. Overall scheme for the half reaction method: Step 1: Split reaction into half-reactions (reduction and oxidation) Step 2: Balance the charge or oxidation number with electrons Step 3: Balance O by adding H2O Step 4: Balance H by adding H+ Step 5: Multiply by some integer to make electrons (lost) = electrons (gained) Step 6: Add half equations and cancel substances on both sides

Example 1. Reaction between manganese (II) ion and the bismuthate ion in acid solution 2+ 5+ 7+ 3+ What are the oxidation numbers for Mn and Bi ? Write the half equation for Mn 2+ Balance O by adding H2O, then H by adding H+ Repeat the process for the bismuthate ion

Balance O by adding H2O, then H by adding H+ We now have the two half equations: Step 5: Multiply by some integer to make electrons (lost) = electrons (gained) Step 6: Add half equations and cancel substances on both sides

8 2 2 16 10 10 30 5 5 15 Step 6: Add half equations and cancel substances on both sides

Overview

Solve these acid solution reactions: : MnO4-  Mn 2+ 2 I-  I2 H2O2  H2O + O2 Cr2O72-  Cr3+

8H+ + MnO4– + 5Fe3+ ➔ 5Fe2+ + Mn2+ + 4H2O Cr2O72- + 3H2O2 + 8H+  2Cr3+ + 3O2 +7H2O