1. Oxidation and Reduction
Chapter 14

2. Oxidation and Reduction
Oxidation - addition of Oxygen.
Reduction - removal of Oxygen.
In terms of electrons
Oxidation is the loss of electrons (OILRIG)
Reduction is the gain of electrons

3. Oxidising and reducing agents
An oxidising agent causes another substance to become oxidised and, in the process, the oxidising agent is reduced. Common oxidising agents include O2, Cl2, ClO-, KMnO4 and H2O2 A reducing agent causes another substance to become reduced and, in the process, the reducing agent is oxidised. Common reducing agents include CO, SO2, SO32- Oxidising agents are useful in Sterilising and Bleaching.

4. Experiments: (a) Halogens as Oxidising agents
Experiments: (a) Halogens as Oxidising agents (b) Displacement reactions of Metals. (See Book Pages )

5. Oxidation Numbers
The oxidation number of an atom is the charge that the atom has or appears to have when electrons are distributed according to certain rule. Rules The ON of an element is 0. The ON of an ion is the charge that it has. The ON of F is always -1. The ON of O IS -2 except OF2 (+2) and H2O2 (-1). The ON of H is +1 except with metal hydrides (-1)

6. Oxidation and reduction in terms of Oxidation numbers
Oxidation is an increase in Oxidation number.
Reduction is a decrease in Oxidation number.
Balancing Redox reactions (See Book Page ) + HANDOUT

7. 2.6.2 Balancing equations using Oxidation Numbers

8. Chemical reactions are all about the movement of electrons
When an equation is balanced the electron movements must balance
Sometimes it is possible to balance an equation in more than one way
It is therefore possible to make the numbers of atoms balance but not the electron movement
Using oxidation numbers prevents this

9. Sequence of events
Write out the formulae of all reactants and products
Assign oxidation numbers to all atoms
Pick out the atoms whose oxidation numbers change
Write down the electron movements
Balance the electron movements
Enter the numbers from balanced electron movement into the overall equation
Balance equation by inspection - [do H last]

10. MnO4- + Fe2+ + H+ = Mn2+ + Fe3+ + H2O +7 -2 +2 +1 +2 +3 +1 -2 5 8 5 4
1. Assign oxidation numbers
(a) Assign Oxidation – increase in Ox. No
(b) Assign Reduction – decrease in Ox. No
2. Select those which change
MnO4- + Fe2+ + H+ = Mn2+ + Fe3+ + H2O 5 8 5 4 +7 +2 +2 +3
Oxidation
Reduction
5. Write electron gains and losses
6. Balance electron transfers 5
Fe = Fe3+
- 1 e- 5 5
Mn = Mn2+
+ 5 e-
7. Put numbers up into the equation
8. Balance equation by inspection - leave H+ till last

11. Sequence of events Write down reactants and products
Assign oxidation numbers
Identify oxidation and reduction
Write down changes and electrons involves
Balance e- change
Put changes into equation
Balance equation by inspection [H last]

12. x2 3 C2H5OH + Cr2O72-+ H+ = CH3COOH + Cr3++ H2O 2 16 3 4 11 -2 +6 +3
1. Assign oxidation numbers
(a) Assign Oxidation – increase in Ox. No
(b) Assign Reduction – decrease in Ox. No
2. Select those which change 3
C2H5OH + Cr2O H+ = CH3COOH + Cr H2O 2 16 3 4 11 -2 +6 +3
Reduction
Oxidation
5. Write electron gains and losses
6. Balance electron transfers 3 12 4 3 x3
C = C2 e- 2
Cr2O = Cr3+ x2 e- 12 6 2 4
7. Put numbers up into the equation
Balance equation by inspection - leave H+ till last :- O 3+(2*7) = (3*2) + x  x=11
H  3(6*1) + X = (3*4) + 11(2*1)  x= 16

13. Examples C2H5OH + MnO41- + H+ = CH3CHO + Mn2+ + H2O
C2H5OH + MnO41- + H+ = CH3COOH + Mn2+ + H2O
Cr2O72- + Fe2+ + H+ = Cr3+ + Fe3+ + H2O
MnO41- + C2O42- + H+ = CO2 + Mn2+ + H2O
Fe2+ + Cl2 = Fe Cl-
MnO41- + H2O2 + H+ = Mn2+ + O2 +H2O
Cr2O72- + CH3OH + H+ = Cr3+ + HCHO + H2O
Cr2O72- + CH3CHO + H+ = Cr3+ + CH3COOH + H2O

14. Answers 5C2H5OH + 2MnO41- + 6H+ = 5CH3CHO + 2Mn2+ + 8H2O
5C2H5OH + 4MnO H+ = 5CH3COOH + 4Mn H2O
Cr2O Fe H+ = 2Cr3+ + 6Fe3+ + 7H2O
2MnO C2O H+ = 10CO2 + 2Mn2+ + 8H2O
2Fe2+ + Cl2 = 2Fe Cl-
2MnO H2O2 + 8H+ = 2Mn2+ + 5O2 +8H2O
Cr2O72- + CH3OH + H+ = Cr3+ + HCHO + H2O
Cr2O72- + CH3CHO + H+ = Cr3+ + CH3COOH + H2O