1. Electrochemistry
Lesson 6
Balancing
Redox
Reactions

2. Balancing Redox Full Reactions in Acid Solution
MnO C2O → MnO CO32-
MnO → MnO2
C2O → CO32-
2MnO C2O H2O + 8H+ → 2MnO2 + 6CO H+ + 4H2O
2MnO C2O H2O → 2MnO2 + 6CO H+
4. Simplify
3. Add the two half reactions
5. Check
2. Balance each half reaction
1. Separate into half reactions 2(
+ 4H+
+ 3e-
+ 2H2O ) 3(
+ 2H2O 2
+ 4H+
+ 2e- ) 2 4

3. Balancing Redox Full Reactions in Basic Solution
2MnO C2O H2O → 2MnO CO H+
2. Add OH- to neutralize the H+
1. Balance in acid solution
4OH-
4OH- 2
4H2O

4. Balancing Redox Full Reactions in Basic Solution
2MnO C2O → 2MnO CO32- +
4OH-
2H2O

5. Balancing Redox Full Reactions in Acid Solution
Fe + O2 → H2O + Fe(OH)3
Fe + → + Fe(OH)3
O2 → H20
4Fe H2O + 3O2 +12H+ → 12H Fe(OH) H2O
4Fe H2O + 3O2 → 4Fe(OH)3 4(
3H2O
3H+
+ 3e -) 3(
4e- +
+ 4H+
+ H2O) 6

6. Balance the redox reaction
As → H2AsO4- + AsH3 (alkaline)
You must separate into two half reactions!
3As H2O H As → 3H2AsO H AsH3
8As H2O → 3H2AsO H AsH3
3OH OH-
3OH As + 9H2O → 3H2AsO AsH3 3( As
H2O →
H2AsO4-
+ 6H+ e- ) 5( )
3H+ + As
+ 3e- →
AsH3 3

7. Balance the redox reaction
IPO4- → IO3- + I PO43- (alkaline)
You must separate into two half reactions!

8. Balance the redox reaction
IPO4- → IO3- + I PO43- (alkaline)
You must separate into two half reactions!
IPO → + PO43-

9. Balance the redox reaction
IPO4- → IO3- + I PO43- (alkaline)
You must separate into two half reactions!
IPO → + PO43-
IPO4- → PO43-

10. Balance the redox reaction
IPO4- → IO3- + I PO43- (alkaline)
You must separate into two half reactions!
IPO → IO3- + PO43-
IPO4- → I PO43-

11. Balance the redox reaction
IPO4- → IO3- + I PO43- (alkaline)
You must separate into two half reactions!
IPO → IO3- + PO43-
2IPO4- → I PO43-

12. Balance the redox reaction
IPO4- → IO3- + I PO43- (alkaline)
You must separate into two half reactions!
IPO H2O → IO3- + PO H+
2IPO4- → I PO43-

13. Balance the redox reaction
IPO4- → IO3- + I PO43- (alkaline)
You must separate into two half reactions!
IPO H2O → IO3- + PO H e-
2IPO e- → I PO43-

14. Balance the redox reaction
IPO4- → IO3- + I PO43- (alkaline)
You must separate into two half reactions!
4(IPO H2O → IO PO H e-)
3(2IPO e- → I PO43-)

15. Balance the redox reaction
IPO4- → IO3- + I PO43- (alkaline)
You must separate into two half reactions!
4(IPO H2O → IO3- + PO H e-)
3(2IPO e- → I PO43-)
12H2O IPO → 3I PO H IO3-
24OH OH-
24OH IPO4- → 3I PO IO H2O
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