1. Redox Reactions.
Reduction
Oxidation

2. Oxidation: Reduction: Gain of oxygen Loss of electrons Loss of oxygen
Gain of electrons
Increase in
oxidation
number
Decrease in
oxidation
number

3. LEO SAYS “GER” ________________ L = Losing E = Electrons O = Oxidation
G = Gaining
E = Electrons
R = Reduction

4. OIL
RIG

5. Oxidation Numbers Rules (Look at your rule list too) The following is not a complete list of rules.
The oxidation number of an atom in an element is zero. E.g. Mg in Mg, O in O2.

6. Oxidation Numbers F -1 O -2 H +1 Cl Oxidation state of C in CO2?
The oxidation numbers of atoms in a compound add up to zero. F -1 O -2 H +1 Cl
Oxidation state of C in CO2?
Oxidation state of C in CO2?
O is -2 (total = – 4)
So C must be = +4
Put the +!

7. Oxidation Numbers F -1 O -2 H +1 Cl +2 Oxidation state of Mg in MgCl2?
The oxidation numbers of atoms in a compound add up to zero. F -1 O -2 H +1 Cl
Oxidation state of Mg in MgCl2? +2

8. Oxidation Numbers F -1 O -2 H +1 Cl -3 Oxidation state of N in NH3?
The oxidation numbers of atoms in a compound add up to zero. F -1 O -2 H +1 Cl
Oxidation state of N in NH3? -3

9. Oxidation Numbers F -1 O -2 H +1 Cl Oxidation state of S in SO42-?
The oxidation numbers of atoms in an ion add up to the charge on the ion. F -1 O -2 H +1 Cl
Oxidation state of S in SO42-?
O = – 2 (total -8)
S = +6
Oxidation state of S in SO42-?
O = – 2 (total -8)
S: X - 8 = -2
Oxidation state of S in SO42-?
O = – 2 (total -8)
S = ???

10. Balanced symbol equation
2 Experiments:
Burning magnesium
Copper in silver nitrate solution
Word equation
Balanced symbol equation

11. 2Mg(s) + O2(g)  2MgO(s) Mg  Mg2+ O  O2-
Oxidized: loss of e-
+2e-
O  O2-
Reduced: gain of e-
+2e-
Put the
e- in.

12. Cu(s) + 2AgNO3(aq)  Cu(NO3 )2(aq) + 2Ag(s)
Complete the half-equations
Cu  Cu2+
Oxidized: loss of e-
+2e-
Ag  Ag
Reduced: gain of e-
+e-

13. Oxidation Numbers F -1 O -2 H +1 Cl -2 Oxidation state of S in S2-?
The oxidation numbers of atoms in an ion add up to the charge on the ion. F -1 O -2 H +1 Cl
Oxidation state of S in S2-? -2

14. Oxidation Numbers F -1 O -2 H +1 Cl -3 Oxidation state of N in NH4+?
The oxidation numbers of atoms in an ion add up to the charge on the ion. F -1 O -2 H +1 Cl
Oxidation state of N in NH4+? -3

15. Oxidation Numbers and names
To avoid any confusion when an element can have several oxidation numbers, the oxidation number is usually mentioned in the compound’s name. In names like “elementate(X)”, the number refers to “element” and not the associated oxygens.
So if we look at some examples , we get the following names:-
KMnO4 potassium manganate(VII)
NaClO3 sodium chlorate(V)
POCl2F phosphorus(V) oxydichlorofluoride
NaH2PO3 sodium dihydrogenphosphate(III)
K2Cr2O7 potassium dichromate(VI)
Check the
numbers.

16. Oxidation #s for each? KMnO4 potassium manganate(VII)
NaClO3 sodium chlorate(V)
POCl2F phosphorus(V) oxydichlorofluoride
NaH2PO3 sodium dihydrogenphosphate(III)
K2Cr2O7 potassium dichromate(VI)

17. Oxidation #s for each? KMnO4 potassium manganate(VII) Mn = +7
O -2 total -8
K = ???
K = 0
K = +1

18. Oxidation #s for each? NaClO3 sodium chlorate(V) Cl = +5
O = -2 (total -6)
Na is Na + 5 – 6 = 0 Na = +1
(which it always is anyways)

19. Oxidation #s for each? POCl2F phosphorus(V) oxydichlorofluoride P = +5

20. NaH2PO3 sodium dihydrogenphosphate(III)
Oxidation #s for each?
NaH2PO3 sodium dihydrogenphosphate(III)
P = +3
O = -2 (total -6)
H = +1 (total +2)
Na = ???
Na = 0
Na = +1

21. K2Cr2O7 potassium dichromate(VI)
Oxidation #s for each?
K2Cr2O7 potassium dichromate(VI)
Cr = +6 (total +12)
O = -2 (total -14)
K = ???
2K +12 – 14 = 0
2K = +2
K = +1

22. Well done!

23. Try Question #1 on homework worksheet