Redox reactions involve the simultaneous oxidation and reduction of reactants. Oxidation is defined as an increase in oxidation state or loss of electrons, while reduction is a decrease in oxidation state or gain of electrons. There are two main methods for balancing redox reactions - the ion-electron method which balances the ions and electrons, and the oxidation state method which balances the changes in oxidation states of elements between reactants and products. Balancing redox reactions involves identifying changes in oxidation states, cross multiplying these changes, and then balancing other elements such as hydrogen and oxygen.

1. Redox Reactions :
Summary
~ Combination of OXIDATION and REDUCTION
~ Definitions :
1.In Terms of Electrons 2.In Terms of Oxidation State
- OiL RiG
In
Oxidation
State
~ Oxidation
~ Reduction
- Oxidation State - Electronegativity Nuclear Charge
Size of Atom
}
 Balancing Chemical Equations :
- Disproportionation - FON
- ION-ELECTRON Method
- OXIDATION-STATE Method
INCREASE
DECREASE}
- Central atom - Add e - Add H1+ OR 1-OH - Add H2O
- Find Oxidation State - Find Change - Cross Multiply
- Balance H & O
2 3 4 5 6 7 8 9 10 11 12 13

2. Redox Reactions
~ Redox
- RED
- OX
~ Reduction
~ Oxidation}
Simultaneously
Definitions :
 In Terms of Electrons
 In Terms of Oxidation State
In Terms of Electrons :
~ Oxidation ~ Reduction
Loss of e1- Gain of e1-
OiL RiG
Examples :
 Al2O3 Al O
Al
Al +
+
+
+
Al3+
Al3+
3e1-
O2 4e1-
O2-
2
O2 O2-
(
) ( )
4 X
3 X
4 3 4 6
}
Al2O3
~ MgF2
1
.
.
. .
. .
.
.
.
Mg 2e1- + Mg2+
F2 + 2e1- 2F1-
Mg + F2 Mg2+ + 2 F1-
Redox Reactions Lecture- 1
AS Level
Chemistry

3. ~Mg3N2
In Terms of Electrons :
~Na2O
Na 1e1- + Na1+
O2 + 4e1-
2O2-
4 Na + O2 4 Na1+ +2 O2-
(
)
4 X
Mg
3Mg +
+
+
+
Mg2+
3Mg2+
2e1-
N2 6e1-
N3-
2
N2 2N3-
(
) ( )
3 X
Redox Reactions Lecture- 1
AS Level
Chemistry

4. In Terms of Oxidation State :
~ Oxidation ~ Reduction
INCREASE
in
Oxidation
State
DECREASE
in
Oxidation
State
IMPORTANCE
-Ionic & Covalent
-To decide redox
reactions easily
-To work-out
Calculations
easily
2
- Oxidation State / Oxidation Number
~ Charge written on AN Atom
- Electronegativity
 Nuclear Charge
 Size of Atom
- MORE
- MORE
- SMALL
HIGHLY
ELECTRONEGATIVE
ELEMENTS
F
O
N
1
2
3

Redox Reactions Lecture- 2
AS Level
Chemistry

5. Across the Period
Down the Group
~ Electronegativity INCREASES
~ Electronegativity DECREASES
- Nuclear Charge Increases
- Radius Increases

6. N2
0
Na
0
Cu
0
H F
1-
1+
H2 S O4
2-
1+ 6+
H2 S O4
1 x 2 + S + ( -2 x 4 ) = 0
2 + S -8 = 0
S -6 = 0
S = + 6
H N O3
2-
1+ 5+
P O4
3-
( )
2-
5+
Cr2 O7
2-
( )
6+ 2-
Mn O4
1-
( )
7+ 2-
~ OF2
~ NaH
~ NCl3
~ PCl5
~ NH3
~ CO
- Challenge YOURSELF
H2O2
O
.
. .
.
.
.
O
.
. .
.
.
. x
x H
H
1-
1- 1+
1+ CH3OH C
H
H
H
O H
1+
2-
2-
1+
1+
1+
- BaO - CH4 - BaO2 - CCl4 - CH2Cl2 - N2H4 - NH2OH
Redox Reactions Lecture- 2
AS Level
Chemistry

7. - Questions :
C + 2 H2 S O4 C O2 + 2 S O2 + 2H2 O
0 1+6+2- 4+ 2- 4+ 2- 1+ 2-
- CARBON
~ Oxidation , Since Oxidation State INCREASES from 0 to 4+
- SULFUR
~ Reduction , Since Oxidation State DECREASES from 6+ to 4+
Reducing Agent / Reductant
Oxidising Agent / Oxidant
- KI – SO2
- KMnO4 – K2Cr2O7
1
Redox Reactions Lecture- 3
AS Level
Chemistry In Terms of Oxidation State

8. 2 N H3 + 3 Cu O N2 + 3 Cu + 3 H2 O
- Questions :
3- 1+ 2+ 2- 0 0 1+ 2-
Pb O2 + 4 H Cl Pb Cl2 + Cl2 + 2 H2 O
2
3
4 Cl2 + H2 O H Cl + H O Cl
5 3 Br2 + 6 Na O H 5 Na Br + Na Br O3 + 3 H2 O
4+ 2- 1+ 1- 2+1- 0 1+ 2-
0 1+ 2- 1+1- 1+2-1+
0 1+2-1+ 1+1- 1+5+2- 1+2-


- Disproportionation
Cu2O + H2SO4 Cu + CuSO4 + H2O
Redox Reactions Lecture- 3
AS Level
Chemistry

9.  Balancing Chemical Equations :
- ION-ELECTRON Method
- OXIDATION-STATE Method
~ IONIC Equations
1 ION-ELECTRON Method :
~ IONIC & MOLECULAR
Equations
RULES
1- Balance the Central atom
2- Balance Oxygen by adding water
3- Balance Hydrogen by adding H1+
4- Balance Charge by adding e
Fe 2+ Fe3+ + 1e 1-
MnO4
1- Mn2+
+ 5e1-
+
8H1+ + 4H2O
Cr2O7
2-
Cr3+
+ 6e1- + 14 H1+
+ 7H2O
2

10. NO2
1-
1 ION-ELECTRON Method :
NO3
1-
+ 2e 1- + 2H 1+
+ H2O
- Questions :
1.The Oxidation of Cr(OH)3 to CrO4
2- in
Alkaline Solution
Cr(OH)3 CrO4
2- + 3 e 1-
+ 5 1- OH + 4 H2O
2.The Reduction of VO2
1+ to V 2+ in Acid Solution
VO2
1+ V2+
+ 3e1- + 4 H 1+ + 2 H2O
The Oxidation of H2C2O4 to CO2 in Acid Solution
3.
+ 2 H 1+
H2C2O4 CO2 + 2 e 1-
4. The Reduction of IO3
1- to I2 in Acid Solution
IO3
1- + 6 H2O
I2
2 + 10 e1- + 12 H1+
2

11. - Questions :
1 ION-ELECTRON Method :
5. The Reduction of O2 in Alkaline Solution
O2
1-OH
+ 4 e 1- + 2 H2O 2
4
The Reduction of H2O2 to Water in Acid Solution
6.
H2O
H2O2 + 2 e 1-+ 2 H1+
The Oxidation of H2O2 to Oxygen in Alkaline
Solution
7.
+ 2 H2O
H2O2 + 2 1- OH O2 + 2 e 1-
Fe 2+ Fe3+ + 1e 1-
MnO4
1- Mn2+
+ 5e1-
+
8H1+ + 4H2O
~ Complete REDOX Equations
( )
2
X 5
5 Fe 2+ + MnO4
1- + 8 H1+ Mn2+ + 5 Fe3+ + 4 H2O
Redox ~ Balancing equations `Slide 9
2 3 4 5 6 7 8 10 11 12 13 BTS

12. ~ Complete REDOX Equations
8. The Oxidation of NO2
1- to NO3
1-with
Manganate (VII) ions, MnO4
1- in Acid Solution
The Reduction of Iodate (V)IO3
1- to Iodine , I2 ,by
Iodide ions, I 1- in Acid Solution
9.
MnO4
1- Mn2+
+ 5e1-
+
8H1+ + 4H2O
NO2
1- + H2O NO3
1- + 2 e 1- + 2 H 1+
(
)
(
)
X 5
X 2
5 NO2
1- + 6 H 1+ + 2 MnO4
1- 5 NO3
1- + 2 Mn 2+ + 3 H2O
2 IO3
1- + 10 e 1- + 12 H 1+ I2 + 6 H2O
2I1- I2 + 2 e 1-
(
)
5 X
10 I 1- + 2 IO3
1- + 12 H 1+ 6 I2 + 6 H2O
Redox ~ Balancing equations `Slide 10
2 3 4 5 6 7 8 9 11 12 13 BTS

13. OXIDATION STATE Method :
2
RULES
1- Identify the elements with Different Oxidation state
2- Deduce the change in oxidation state
3- Cross Multiply the Change
4 - Balance Other Elements like Hydrogen & Oxygen
…. Fe 2+ +….MnO4
1- +….H1+ ….Mn2+ + ….Fe3+ + …. H2O
1
5 5
1 4
8
2+ 3+
7+ 2+
( 1 ) ( 5 )
…. Fe 2+ +….MnO4
1- +….H1+ ….Mn2+ + ….Fe3+ + …. H2O
1
5 5
1 4
8
Redox ~ Balancing equations `Slide 11
2 3 4 5 6 7 8 9 10 12 13 BTS

14. ...SO2 +…Cr2O7
2- + ..H1+ ...SO4
2- + ..Cr 3+ + ..H2O
OXIDATION STATE Method :
2
- Questions :
4+ 6+
6+ 3+
( 2 ) ( 6 )
( 3 )
( 1 ) - Take COMMON , If Any
- For ALL Atoms
...SO2 +…Cr2O7
2- + ..H1+ ...SO4
2- + ..Cr 3+ + ..H2O
3 1 3 2 1
2
3 1 2 3 2 1
….H2SO4 +…. HI …. S +….. I2 +…..H2O
….H2SO4 +…. HI ….H2S +….. I2 +…..H2O
….H2SO4 +…. HBr ….SO2 +….. Br2 +…..H2O
1 6 1 3 4
1 8 1 4 4
1 2 1 1 2
Redox ~ Balancing equations `Slide 12
2 3 4 5 6 7 8 9 10 11 13 BTS

15. …V3+ + …I2 + …H2O …I1- + …VO 2+ +… H1+
OXIDATION STATE Method :
2
- Questions :
2 1 2 2 2 4
….Cu + ….H1+ +…NO3
1- ..Cu2+ + …NO2 + …H2O
….Cu + ….H1+ +…NO3
1- ..Cu2+ + …NO + …H2O
1 4 2 1 2 2
3 8 2 3 2 4
...SO2 +….H2O +….Ag1+ …Ag +….SO4
2- + ….H1+
1 2 2 2 1 4
…Fe2+ + ….ClO3
1- + ….H1+ …Cl 1- + ….Fe 3+ + ….H2O
6 1 6 1 6 3
Redox ~ Balancing equations `Slide 13
2 3 4 5 6 7 8 9 10 11 12 BTS