SAMPLE PROBLEM 21.1 Balancing Redox Reactions by the Half Reaction Method it Pro

Question

SAMPLE PROBLEM 21.1 Balancing Redox Reactions by the Half Reaction Method it Problem Permanganate ion is a strong oxidizing agent, and its deep purple color makes useful an indicator in redox titrations. It reacts in basic solution with the oxalate for form carbonate ion and solid manganese dioxide. Balance the skeleton ionic equation the reaction between NaMno, and Na2C204 in basic solution: Mno. (aq) C204 (aa) Mnoz(s) co32 (aa) [basic solution) Plan we proceed through step 4 as if this took place in acidic solution. Then, we add the appropriate number of OH ions and cancel excess H20 molecules (step 4 Basic). Solution 1. Divide into half-reactions. CO C2O. 4 Mno2 MnO. 2. Balance. a. Atoms other than O and H, a. Atoms other than O and H. 2CO. C,O Not needed b. O atoms with H2O, b. o atoms with H2O 2CO. C,O, 2H3O Mno4 Mno2 2H20 c. H atoms with H c. H atoms with H 2H20 C2042 2CO 4H Mno4 Mno2 2H2O d. Charge with e d. Charge with e 2CO 4H 2e 2H3O C,O MnO2 2H2O 3e 4H Mno4 [oxidation] [reduction] Multiply each halfreaction, if necessary, by some integer to make e lost equal e gained. 4H+ 2e) 3 (2H20 C20. Mno2 2H20) 2CO. Mno4 203e 12H+ 6e 2Mno, 2Mno2 4H20 6H2O 3C20. 6CO 4. Add half reactions, and cancel substances appearing on both sides. four H2o cancel to leave two Ho The six e eight H' cancel to leave four H on the right, and

Explanation / Answer

Note that we are balancing this via redox method

this implies:

1) balance atoms of interest other than Oxygen and Hydrogen

2) balance Oxygen, by adding H2O

3) balance Hydrogen by adding H+

4) balance charge

5) balance atoms

6) add all

7) cancel common terms

8) this is your final equation

We add H2O because it is easier to manipulate via H+ and O

If we just added Oxygen, we could not balance Hdyrogen eventually, and the overall charge will not get the same

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