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Class notes chemistry Chemistry Simplified NCERT Class 11
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Class notes chemistry Chemistry Simplified NCERT Class 11
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UNIT 8 REDOX REACTIONS1. CLASSICAL CONCEPT OF OXIDATION AND REDUCTION
Oxidation
Oxidation is defined as addition of oxygen or any other electronegative component
Or removal of hydrogen or any other electropositive component.
2H 2 O 2 2H 2 O
H 2 S Cl 2 2HCl S
Reduction
Reduction is defined as addition of hydrogen or any other electropositive component
Or removal of oxygen or any other electronegative component.
2 H 2 O 2 2H 2 O
H 2 S C l 2 2H C l S
Oxidising Agent
A substance which provides oxygen or any electronegative element
Or removes hydrogen or any other electropositive element is called an oxidising
agent.
In the above examples, O2 and Cl2 act as oxidising agents.
Reducing Agent
A substance which provides hydrogen or any electropositive element or removes
oxygen or any electronegative element is called a reducing agent.
NOTE
During a redox reaction, a reducing agent undergoes oxidation while oxidising agent
undergoes reduction.
2. ELECTRONIC CONCEPT OF OXIDATION AND REDUCTION
Oxidation
Oxidation is the process involving loss of electrons.
Reduction
Reduction is the process involving gain of electrons.
Oxidising Agent
An oxidising agent is a substance whose atoms gain electrons.
Reducing Agent
A reducing agent is a substance whose atoms lose electrons.
Zn C u 2 Zn 2 C u
PREPARED BY HAIZEL G. ROY, HSST (HG) CHEMISTRY, GOVT. H.S.S. KALAMASSERY ERNAKULAM Page | 1
, Here Zn atom loses electrons while Cu2+ ions gains electrons.
So Zn is oxidized and Cu2+ is reduced.
Cu2+ is the oxidising agent and Zn is the reducing agent.
OXIDATION HALF AND REDUCTION HALF REACTIONS
Every redox reaction consists of two half cell reactions.
They are oxidation half reaction and reduction half reaction.
Eg:- Reaction between Na and Cl.
Na atom loses an electron to form Na+.
+ -
Na Na + 1e
Cl atom gains an electron to form Cl ─.
- -
Cl + 1e
Cl
Overall cell reaction (Redox reaction) is
+ -
Na + Cl
Na + Cl
Redox Reaction
A chemical reaction in which both oxidation and reduction reactions occur
simultaneously is called a redox reaction.
Example-1
A clean Zn strip is placed in a solution of CuSO4 placed in a beaker.
The following changes are observed.
Zn metal starts to dissolve and as a result of this, its mass decreases.
Cu metal starts to deposit.
The blue colour of CuSO4 solution begins to fade.
The reaction proceeds with the evolution of heat.
Reactions
2+ -
Zn
Zn + 2e
2+ -
Cu + 2e
Cu
2+ 2+
Zn + Cu
Zn + Cu
Example-2
A clean copper strip is placed in a solution of AgNO3 kept in a beaker.
The following changes are observed.
Copper strip starts to dissolve and as a result its mass decreases.
Silver starts to deposit.
Blue colour of Cu2+ ions appear.
Reaction proceeds with the evolution of heat.
PREPARED BY HAIZEL G. ROY, HSST (HG) CHEMISTRY, GOVT. H.S.S. KALAMASSERY ERNAKULAM Page | 2
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