SUBJECT: CHEMISTRY TOPIC : Oxidation and Reduction for grade 10 and 11.IGCSE,MYP,CBSE,SSC and other boards

1. Topic 7
OXIDATION AND REDUCTION

2. Objectives
Core
 Oxidation (in terms of hydrogen
and oxygen)
 Reduction (in terms of hydrogen
and oxygen)
 Redox Reaction
 Oxidizing agent
 Reducing agent
Extended
 Electronic concept of oxidation and
reduction .
 Oxidation state
 Half reaction
 Ionic equation
 Oxidizing and reducing agents used
in Lab

4.  We saw few images in the previous slide ,could you say what is common in
them ??
 Well these all are examples of oxidation – reduction reaction.
 Iron deposits a brown layer of oxide called rust
 apple slice gets brown after sometime due to its reaction with oxygen from
air.
 Fire needs oxygen to begin and working of a battery involve transfer of
electron . These all reactions are example of Oxidation – Reduction reaction,

5. Oxidation
 oxygen is gained ( added).
eg . Mg burns in air with a dazzling flame to produce white MgO
2Mg + O2  2MgO
here Mg is oxidised as it adds up oxygen
 Hydrogen is lost (removed).
eg Reaction of methane with Chlorine.
CH4 + Cl2  CH3Cl + HCl
Methane is oxidised because it lost its one hydrogen.

6. Reduction
 Oxygen is lost (removed)
Eg, Reaction of Mg with PbO yields MgO and Pb atom
Mg + PbO  MgO + Pb
Pb is reduced as it lost oxygen .
 Hydrogen is gained ( added)
eg, when Hydrogen reacts with copper oxide it gives Cu and water molecule
 CuO + H2  Cu + H2O
In the reaction oxygen has gained hydrogen so its reduced.

7. Another definition for oxidation
and reduction
 Oxidation is Loss of electron
We know metals have a tendency to lose electron and form a cation
during a chemical reaction. This is oxidation.
Eg
During the formation of common salt ,sodium atom loses one(outermost)
electron to form Na+ cation.
 Na – 1e-  Na+
sodium is oxidised .

8. Another definition for oxidation
and reduction
 Reduction is gain of electron
During the formation of common salt( NaCl) sodium loses one electron and
oxidizes, this electron is gained by Chlorine atom and it forms a Cl- anion
Cl – 1e-  Cl-
Here Cl atom is being reduced.
The overall reaction goes like this
Na+ + Cl-  NaCl

10. Oxidation- Reduction and
oxidation state
 Oxidation state tells us how many electrons each atom of an element has
gained, lost, or shared, in forming a compound.
 Each atom in a formula has an oxidation state.
 The oxidation state is usually given as a Roman numeral. Note these Roman
numerals: 0 I II III IV V VI VII
 Where an element is not combined with other elements, its atoms are in
oxidation state 0.
 The sum of oxidation states of all atoms in a (Neutral) molecule is 0.

11. Oxidation state of some
elements

12. Oxidation state of some
Transition elements

13.  Increase in oxidation state is defined as Oxidation.
 Decrease in oxidation state is defined as Reduction.
Eg
 During the formation of NaCl the oxidation state of sodium increases from 0
to 1 and that of Chlorine it decrease from 0 to -1.
2Na + Cl2  2NaCl

14. Half reactions and Redox Reaction
 Loss of electron (oxidation) Or gain of electron(reduction) is known as a half
reaction . Like if we recall the formation of common salt , we have
Na – 1e-  Na+ (oxidation half reaction) and
Cl – 1e-  Cl- (reduction half reaction)
Both the half reactions have to combine to give the overall reaction known as Redox
reaction . Ie Na+ + Cl-  NaCl
We can now define Redox reaction as “Reduction and oxidation always takes
place simultaneously that is known as a Redox reaction”

15. More examples of redox reaction

16. Oxidizing and Reducing agents
 In a Redox reaction the substance that is oxidized is known as a Reducing
agent and the substance that is reduced is known as Oxidizing agent.
When hydrogen reacts with heated copper(II) oxide, the reaction is:
CuO (s) + H2 (g)  Cu (s) + H2O (l)
 The copper(II) oxide is reduced to copper by reaction with hydrogen. So
hydrogen acts as a reducing agent.
 The hydrogen is itself oxidized to water, in the reaction. So copper(II) oxide
acts as an oxidizing agent.
 Oxidising agents are also called oxidants. Reducing agents are called
reductants.

17. Oxidising and reducing agents in
the lab
Potassium manganate(VII): an oxidising agent is in oxidation state + VII. But it is
much more stable in oxidation state + II. It easily takes electrons from other
substances, in the presence of a little acid. It is itself reduced in the reaction –
with a colour change from purple to colourless.

18.  Potassium dichromate(VI): an oxidizing agent is also a transition element, and
can exist in different oxidation states. In potassium dichromate(VI) it is in
oxidation state + VI. But oxidation state + III is the most stable. So potassium
dichromate(VI) is a strong oxidizing agent, in the presence of acid. It reacts to
gain electrons and reduce the oxidation state to + III. Once again there is a
colour change on reduction from orange to green

19.  Potassium iodide: a reducing agent When its solution is added to hydrogen
peroxide, in the presence of sulfuric acid, this redox reaction takes place:
H2O2 + 2KI (aq) + H2SO2 (aq)  I2 (aq) + 1 K2SO2 (aq) + 2H2O (l)
We can see that the hydrogen peroxide loses oxygen.it is reduced. The
potassium iodide acts as a reducing agent and is oxidised to iodine. This
causes a colour change.

20. THANK YOU