1. Electrochemistry
Lesson 3
Oxidation Numbers

2. Ho Ho Ho
Silver crystals
on a copper frame

3. Oxidation Numbers
HV2O4-  V6+
Is the above equation oxidation or reduction?
Oxidation numbers are assigned numbers that are used to determine if oxidation or reduction has occurred.

4. Rules for Oxidation Numbers Oxidation #
1. All elements are zero: N2 Pb Na O2

5. Rules for Oxidation Numbers Oxidation #
2. Monatomic Ions are their charge
Na+ +1 -1
Br- +2
MgSO4 -2
Al2S3

6. Rules for Oxidation Numbers Oxidation #
3. O in a compound is -2
exception: peroxides -1
Na2O -2
CO2 -2 O2
CH3COOH -2 -1
exception
HOOH

7. Rules for Oxidation Numbers Oxidation #
4. H in a compound is +1
exception: metal hydrides -1
H2O +1 +1
C12H22O11 H2 -1
NaH

8. oxidation #s SO42- Total charge +6 -2 -2 x 4 +6 -8 = -2
Rules for Oxidation Numbers
5. The sum of the oxidation numbers must equal the charge
oxidation #s
SO42-
Total charge +6 -2
-2 x 4 +6 -8
= -2

9. oxidation #s
PO43-
Total charge +5 -2 +5 -8
= -3

10. oxidation #s
Cr2O72-
Total charge +6 -2
12 / 2
+12
-14
= -2

11. Ca(NO3)2 +2

12. Na2C4O8 +1
+7/2 -2 +2
+14
-16
= 0

13. CH3COOH

14. Rewrite
C2H4O2 +1 -2 +4 -4
= 0

15. Zn(OH)42- +2 -2 +1 +2 -8 +4
= -2

16. H2PtCl6 +1 +4 -1 +2 +4 -6
= 0

17. H3PO3 +1 +3 -2 +3 +3 -6
= 0

18. Al(NO3)3 +3 +5 -2 +3
+15
-18
= 0

19. Na2O2
Exception - does not work, O must be -1 +1 -1 -2 +2 -2 -4
= 0

20. CaH2 +2 +1 -1 +2 +2 -2
= 0
Exception - does not work, H must be -1

21. Fe(H2O)5(OH)2+

22.
Fe(H2O)5(OH) ? = +2

23.
Fe(H2O)5(OH) = +2

24. Is the above equation oxidation or reduction?
Oxidation Numbers
HV2O4-  V6+
Is the above equation oxidation or reduction?
Increase +6 +3
If the oxidation number increases it is oxidation.

25. Using Oxidation Numbers
If the oxidation number of the central atom increases going from left to right, its oxidation.
ClO2-  ClO4-
Increase is oxidation +3 +7
oxidation
reducing agent
4 electrons lost

26. Using Oxidation Numbers
If the oxidation number of the central atom decreases going from left to right, its reduction.
NO3-  HNO2 +5 +3
decrease is reduction
reduction
2 electrons gained
oxidizing agent

27. Label the oxidizing agent and the reducing agent.
ReO4- + IO-  IO3- + Re
Reduced Oxidized
Ox Agent Red Agent

28. Label the oxidizing agent and the reducing agent. +3 +5 +5 +2
3As2O NO H2O + 4H+  6H3AsO NO
oxidized reduced
red agent ox agent
Numa Numa