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. Oxidized – gains oxygen
2Mg(s) + O2(g)  2MgO(s)
Must be a redox!
Mg  Mg2+
Oxidized – loss of e-
+2e-
Put the
e- in.
O  O2-
Reduced – gain of e-
+2e-

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

5. Summation of the Oxidation Rules
The oxidation number of a free element is zero
Examples of free elements
Gold - Au
Zinc –Zn
The oxidation number of a monatomic ion is equal to its charge
Examples of monatomic ions
Sodium ion - Na+1
Chloride ion - Cl-1

6. Examples of polyatomic ions Phosphate - PO4-3 Carbonate - CO3-2
3. The sum of the oxidation numbers in the formula of a polyatomic ion is equal to its charge.
Examples of polyatomic ions
Phosphate - PO4-3
Carbonate - CO3-2
4. The sum of the oxidation number in the formula of a compound is equal to zero
Examples of compounds
Water - H2O
Glucose - C6H12O6

7. Example of a peroxide Hydrogen peroxide - H2O2
5. In compounds, Hydrogen has an oxidation number of +1
6. In compounds, Oxygen has an oxidation number of -2
7. In peroxides, oxygen has an oxidation number of -1
Example of a peroxide
Hydrogen peroxide - H2O2

8. Oxidation Numbers Oxidation state of C in CO2? ? – 4 = 0 ? = +4
The oxidation numbers of atoms in a compound add up to zero.
Oxidation state of C in CO2?
? – 4 = 0
? = +4
Put the +!

9. +2 Oxidation Numbers Oxidation state of Mg in MgCl2?
The oxidation numbers of atoms in a compound add up to zero.
Oxidation state of Mg in MgCl2? +2

10. -2 Oxidation Numbers Oxidation state of S in S2-?
The oxidation numbers of atoms in an ion add up to the charge on the ion.
Oxidation state of S in S2-? -2

11. -3 Oxidation Numbers Oxidation state of N in NH3?
The oxidation numbers of atoms in a compound add up to zero.
Oxidation state of N in NH3? -3

12. Oxidation Numbers Oxidation state of S in SO42-? ? – 8 = -2 ? = +6
The oxidation numbers of atoms in an ion add up to the charge on the ion.
Oxidation state of S in SO42-?
? – 8 = -2
? = +6

13. -3 Oxidation Numbers Oxidation state of N in NH4+?
The oxidation numbers of atoms in an ion add up to the charge on the ion.
Oxidation state of N in NH4+? -3

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

15. Lets Practice H2SO3 + I2 + H2O → H2SO4 + HI
Oxid. #
H2SO3 + I2 + H2O → H2SO4 + HI
Total
FeCl3 + SnCl2 → FeCl2 + SnCl4

16. Lets Practice AgNO3 + NaClO + AgCl → AgClO3 + NaNO3
Oxid. #
AgNO3 + NaClO + AgCl → AgClO3 + NaNO3
Total
MnO2 + FeSO4 + H2SO4 → MnSO4 + Fe2(SO4)3 + H2O

17. Lets Practice Mn(NO3)2 + PbO2 + HNO3+ → HMnO4 + Pb(NO3)2 + H2O
Oxid. #
Mn(NO3)2 + PbO2 + HNO3+ → HMnO4 + Pb(NO3)2 + H2O
Total
HMnO4 + HNO3 + Mn(NO3)2→ MnSO4 + H2O +O2

18. Answers to Practice quest
11. R= Au O= I R. A.= KI O. A.= AuCl3 12. R= N O= Ag R. A.= Ag O. A.= HNO3 13. R= Fe O= Sn R. A.= SnCl2 O. A.= FeCl3 14. R= N O= Fe, S R. A.= FeS O.A.= HNO3 15. R= Cu O= I R. A.= KI O. A.= CuSO4 16. R= I O= H R.A.= H2 O.A.= KIO3 17. R= Cl O= Cl R.A.= NaClO O. A.= NaClO 18. R= O O= Mn R. A.= MnO2 O. A.= O2 19. R= Mo O= I R. A.= KI O. A.= MoO3 20. R= Br O= Mn R. A.= MnCl2 O. A.= Br2