1. Oxidation - Reduction Reactions
Chapter 4.9
Oxidation - Reduction Reactions
“Redox Reactions”

2. Redox Reactions
Reaction in which one or more electrons are transferred
Oxidation states (numbers) change
Examples:
Na (s) + Cl2 (g) NaCl (s)
CH4 (g) + O2 (g) CO2 (g) + H2O (g)

3. Assigning Oxidation Numbers (states)
1. The oxidation number of an uncombined element is zero
2. The oxidation number of a monatomic ion is equal to its charge (Group 1 is +1 and Group 2 +2)

4. 3. The oxidation number of oxygen in compounds is -2 (except in peroxide, -1)
4. The oxidation number of hydrogen in compounds is +1 (except in a metal hydride, -1)

5. 5. The sum of the oxidation numbers in for an electrically neutral compound is ZERO
6. The sum of the oxidation numbers in the formula of a ion is equal to its charge

6. PRACTICE....Assign oxidation numbers to all of the atoms in the following compounds:
2. SF6
3. FeO
4. KMnO4
5. PbCO3
6. CO3-2

7. Assigning Oxidation Numbers
TIME TO PRACTICE!
Assigning Oxidation Numbers

8. Oxidation and Reduction
An old memory device for oxidation and reduction goes like this…
LEO says GER
Lose Electrons = Oxidation
Gain Electrons = Reduction

9. Oxidation and Reduction
Another memory device goes like this…
“OIL RIG”
Oxidation Is Loss
Reduction Is Gain

10. Oxidation Reduction Reactions (Redox)
Each sodium atom loses one electron:
Each chlorine atom gains one electron:

11. LEO says GER :
Lose Electrons = Oxidation
Sodium is oxidized
Gain Electrons = Reduction
Chlorine is reduced

12. OIL RIG :
Oxidation Is Loss of electrons
Sodium is oxidized
Reduction Is Gain of electrons
Chlorine is reduced

13. Reducing Agents and Oxidizing Agents
The substance reduced is the oxidizing agent
The substance oxidized is the reducing agent
Sodium is oxidized – it is the reducing agent
Chlorine is reduced – it is the oxidizing agent

14. 14

15. Assigning Oxidation numbers in a Redox Reaction
Zn(s) + 2HCl(aq) ZnCl2(aq) + H2(g)
SiCl4(l) + 2Mg(s) MgCl(s) + Si(s)
2AgNO3(aq) + Cu(s) Cu(NO3)2(aq) + 2Ag(s)

16. Not All Reactions are Redox Reactions
Reactions in which there has been no change in oxidation number are not redox rxns
Examples:

17. Trends in Oxidation and Reduction
Active metals:
Lose electrons easily
Are easily oxidized
Are strong reducing agents
Active nonmetals:
Gain electrons easily
Are easily reduced
Are strong oxidizing agents