11C08

Redox Reaction

11C08.1

Introduction to Redox Reaction

Battery

Combustion

Rusting

Refining of Impure metal

Examples of Redox Reaction

Learning Objectives

Classical and electronic concept of Oxidation and Reduction

Oxidation number

11C08.1 Introduction to Redox Reaction

11C08.1

CV 1

Classical and Electronic

Concept of Oxidation and Reduction

Redox = Reduction + Oxidation

The reaction in which oxidation and reduction reactions occur simultaneously.

Redox Reaction

Oxidation

Addition of oxygen/electronegative element to a substance

Removal of hydrogen/electropositive element from a substance

Classical Concept

Addition of hydrogen/electropositive element to a substance

Removal of oxygen/electronegative element from a substance

Reduction

Classical Concept

Transfer of electron

Electronic Concept

Transfer of electron

Loss of electron

Electronic Concept

Oxidation

Increase in positive charge

Decrease in negative charge

Loss of electron

Electronic Concept

Decrease in positive charge

Increase in negative charge

Reduction

Gain of electron

Electronic Concept

Example-

Electronic Concept

Intensity of blue colour is reduced

Initial stage

Intermediate stage

Final stage

Cu⁺² deposited

as Cu

Zn rod

Electron Transfer Reactions

Intensity of blue colour is reduced

Initial stage

Intermediate stage

Final stage

Cu⁺² deposited

as Cu

Release of 2e^-

Gain of 2e^-

Zn rod

Electron releasing tendency of the metals : Zn > Cu

Electron Transfer Reactions

Blue colour starts developing

Initial stage

Intermediate stage

Final stage

Ag deposited

Cu rod

Intensity of blue

colour increases

Electron Transfer Reactions

Blue colour starts developing

Initial stage

Intermediate stage

Final stage

Ag deposited

Cu rod

Electron releasing tendency of the metals : Cu > Ag

Release of 2e^-

​

Gain of 2e^-

​

Intensity of blue

colour increases

Electron Transfer Reactions

Oxidation

Reduction

1. Addition of oxygen/electronegative element to a substance

​

2. Removal of hydrogen/electropositive element from a substance

1. Removal of oxygen/electronegative element from a substance

2. Addition of hydrogen/electropositive element to a substance

3. Loss of electron

3. Gain of electron

11C08.1

CV 2

Oxidation Number

Real or imaginary charge on an atom in the compound

.

.

.

.

High E.N.

-1

+1

Oxidation Number (O.N.)

1. In elements, in the free or the uncombined state, each atom bears an

oxidation number of zero

0

0

.

.

.

0

0

.

.

.

.

.

.

.

0

0

0

0

Rules for Calculating Oxidation Number

.

.

2. For ions composed of only one atom;

​

O.N. = charge on the ion.

O.N.= +1

O.N.= +2

O.N.= -1

• O.N. of Alkali metal in their compounds= +1
• O.N. of Alkaline earth metal in their compounds = +2
• O.N. of Aluminum in its all compounds = +3

NOTE:

Rules for Calculating Oxidation Number

3. O.N. of oxygen :

O.N.= -2

O.N.= -1

+1

+1

+1

-1

-1

+1

-1

-1

.

.

0

0

Rules for Calculating Oxidation Number

O.N.= +1

O.N.= +2

-1

+1

-1

-1

+1

-1

+1

0

0

.

.

+1

Rules for Calculating Oxidation Number

4. O.N. of Hydrogen :

O.N.= +1

• Exception- When H is bound to metal, O.N. = -1

​

e.g. - LiH, NaH, CaH₂

+1

-1

-1

+1

O.N.= -1

• Mostly +1

Rules for Calculating Oxidation Number

5.

O.N. = -1,

halide ion

Cl, Br and I when combine with oxygen

(oxoacid and oxoanion)

Positive oxidation number

O.N=+7

O.N=+7

Rules for Calculating Oxidation Number

6. For a comound :

Algebraic sum of O.N. of all the atoms = 0

7. For polyatomic ion :

Algebraic sum of O.N. of atoms = Charge on the ion.

Rules for Calculating Oxidation Number

Rules for Calculating Oxidation Number

0

-2

+2

0

0

0

-2

+2

Individual Oxidation Number

0

-2

+2

0

0

-2

= +2+0

= +2

0

Individual Oxidation Number

-2

+2

0

0

-2

= 0+0

= 0

+2

0

0

Individual Oxidation Number

0

-2

0

0

-2

= 0+(+2)

= +2

+2

0

Individual Oxidation Number

.

.

.

.

-2

+2

-2

+2

-2

+2

+2

+2

-2

-2

-2

-2

-2

+2

+2

+2

0

0

0

0

Individual Oxidation Number

.

.

.

.

-2

-2

-2

+2

+2

-2

-2

-2

-2

-2

+2

+2

+2

0

0

0

= +2+2+2+0

= +6

0

Individual Oxidation Number

.

.

.

.

-2

+2

-2

+2

-2

+2

-2

-2

-2

-2

-2

+2

+2

+2

0

0

= +2+2+0+0

= +4

0

0

Individual Oxidation Number

.

.

.

.

-2

+2

-2

+2

-2

+2

+2

+2

-2

-2

-2

-2

-2

0

0

0

= +2+2+2+0

= +6

0

Individual Oxidation Number

.

.

.

.

.

.

-1

+1

+2

-2

-2

-2

-2

.

.

.

.

-1

+1

+2

+2

+2

0

0

0

0

0

0

Individual Oxidation Number

.

.

.

.

.

.

-1

-2

-2

.

.

.

.

-1

+1

0

0

0

0

0

= +2+2+1+0

= +5

-2

-2

+2

+2

Individual Oxidation Number

.

.

.

.

.

.

-1

+1

+2

-2

-2

.

.

.

.

-1

+1

+2

0

0

0

0

= 0+0

= 0

-2

-2

+2

+2

Individual Oxidation Number

.

.

.

.

.

.

-1

+1

+2

-2

-2

.

.

.

.

-1

+1

+2

0

0

0

0

= 0+0

= 0

-2

-2

+2

+2

Individual Oxidation Number

.

.

.

.

.

.

-1

+1

+2

-2

-2

-2

.

.

.

.

-1

+2

0

0

0

0

0

= +2+2+1+0

= +5

+2

+1

-2

-2

+2

Individual Oxidation Number

Alfred Stock

Example :–

​

Stannous chloride : Sn(II)Cl₂

​

Stannic chloride : Sn(IV)Cl₄

Stock Notation

Reducing agent (R.A.)/Reductants :

A reagent which can O.N. of the element in the substance

Oxidizing agent (O.A.)/Oxidants :

A reagent which can O.N. of the element in the substance

Redox reaction - Reactions which involve change in O.N.

+1

-2

+1

-2

0

+4

-2

Reduction

Oxidation

Example-

Oxidation

Reduction

1. Addition of oxygen/electronegative element to a substance

​

2. Removal of hydrogen/electropositive element from a substance

1. Removal of oxygen/electronegative element from a substance

2. Addition of hydrogen/electropositive element to a substance

3. Loss of electron

3. Gain of electron

11C08.1

PSV 1

Sol.

Oxidation

+3

+7

+2

+4

Reduction

ConcepTest

Ready for a Challenge

Pause the video

Time duration : 1 minute

Q.

O.N=+7

-2

+2

+2

-2

+2

-2

+1

-1

O.N=+7

+1

-1

-2

+2

+2

-2

+2

-2

+1

-1

Sol.

Q.

Summary

Redox Reaction - The reaction in which oxidation and reduction reactions

occur simultaneously.

Oxidation Number(O.N.)- It represents the real or imaginary charge on an

atom or element in the compound

Oxidation

Reduction

1. Addition of oxygen/electronegative element to a substance

1. Removal of oxygen/electronegative element from a substance

2. Removal of hydrogen/electropositive element from a substance

2. Addition of hydrogen/electropositive element to a substance

3. Loss of electron

3. Gain of electron

4. O.N. of the element in the given substance

4. O.N. of the element in the given substance

Reference Questions

NCERT Exercises: 1, 2, 3, 5, 6, 7, 8, 9, 10, 11, 13, 14, 16, 17, 22

NCERT In text : 1, 2, 3, 4

Workbook Questions : 1, 2, 3, 4, 11, 12, 13, 16

11C08.1 Introduction to Redox Reaction

11C08.2�Types of Redox Reaction

Learning Objectives

​

Combination and Decomposition Reaction

Displacement Reaction

Disproportionation Reaction

​

11C08.2 Types of Redox Reactions

11C08.2

CV 1

Combination and

Decomposition Reaction

Combination reaction may be denoted as:

Either one must be in

elemental form

Combustion Reactions

Combination Reaction

Combination reaction may be denoted as:

Either one must be in

elemental form

Combustion Reactions

Which make use of elemental dioxygen,

are redox reaction

Combination Reaction

Combination reaction may be denoted as:

Either one must be in

elemental form

Combustion Reactions

Which make use of elemental dioxygen,

are redox reaction

Other Reactions

Combination Reaction

Opposite of combination reactions

Breakdown of a compound into two or more components

One of them must be in elemental state

Decomposition Reaction

All decomposition reactions are not redox reaction

No change in O.N.

Decomposition Reaction

All decomposition reactions are not redox reaction

No change in O.N.

Decomposition Reaction

11C08.2

CV 2

Displacement Reaction

An ion (or an atom) in a compound is replaced by an ion (or an atom) of another element

Two types

Metal displacement

Non-metal displacement

+

+

Replaces

Displacement Reactions

A metal in a compound can be displayed by another metal

in the uncombined state

Finds application in purification of metals

Metal Displacement

A metal in a compound can be displayed by another metal

in the uncombined state

Finds application in purification of metals

Reduced

Metal Displacement

A metal in a compound can be displayed by another metal

in the uncombined state

Finds application in purification of metals

Oxidised

Metal Displacement

A metal in a compound can be displayed by another metal

in the uncombined state

Finds application in purification of metals

Reduced

Metal Displacement

A metal in a compound can be displayed by another metal

in the uncombined state

Finds application in purification of metals

Oxidised

Metal Displacement

Zn > Cu > Ag

Metal activity series

It includes hydrogen displacement and a rarely occurring reaction

involving oxygen displacement

Water

Sodium

Fire

Non-metal Displacement

It includes hydrogen displacement and a rarely occurring reaction

involving oxygen displacement

Water

Sodium

Fire

Non-metal Displacement

It includes hydrogen displacement and a rarely occurring reaction

involving oxygen displacement

Water

Sodium

Fire

Non-metal Displacement

Production of dihydrogen gas

Non-metal Displacement

Many metals are capable of displacing hydrogen from acids

Metals

Acids

Dihydrogen gas

Salt

+

+

Non-metal Displacement

Non-metal Displacement

9

F

17

Cl

35

Br

53

I

Halogens

Displacement reactions of Cl, Br and I using fluorine are

not carried out in aqueous solution

Halogen Activity Series

Chlorine can displace bromide and Iodide ions in an aqueous solution

Gives colour

Layer Test

Halogen Activity Series

Bromine can displace Iodide ion in solution

Halogen displacement reaction have industrial application

Halides

Halogen

Oxidation Process

Recovery

strongest oxidising agent

Fluorine cannot recover from this method

Halogen Activity Series

11C08.2

CV 3

Disproportionation Reaction

An element is simultaneously oxidised and reduced

One of the reacting elements should exist in atleast three oxidation state

Disproportionation Reaction

• P, S and Cl undergo disproportionation in alkaline medium :

Disproportionation Reaction

• P, S and Cl undergo disproportionation in alkaline medium :

Disproportionation Reaction

Oxidises colour bearing stains of the

substance to colourless compounds

• P, S and Cl undergo disproportionation in alkaline medium :

Disproportionation Reaction

Fluorine reacts with alkali as:

Being most E.N. element,

it cannot exhibit any positive oxidation state

F does not exhibit disproportionation tendency

Exception of Disproportionation Reaction

ConcepTest

Ready for a Challenge

Q.

Pause the video

Time duration: 2 minute

Identify Disproportionation Reaction

Sol.

-1

Ans-(D)

Q.

Identify Disproportionation Reaction

Summary

• All combustion reactions, which make use of elemental dioxygen, as well as other reactions involving elements other than dioxygen, are redox reaction

• Decomposition reaction leads to the breakdown of a compound into two or more components

• In a disproportionation reaction an element in one oxidation state is simultaneously oxidised and reduced

• In a displacement reaction, an ion (or an atom) in a compound is replaced by an ion (or atom) of another element

Reference Questions

NCERT Exercises : 8.4, 8.15, 8.24 and 8.28

NCERT In text : 5, 6 and 7

Workbook Questions : 5 and 19

11C08.2 Types of Redox Reactions

11C08.3�Balancing of Redox Reaction

Learning Objectives

​

Oxidation number method

Half reaction method

​

11C08.3 Balancing of Redox Reaction

11C08.3

CV 1

Oxidation number method

Lets take an example of unbalanced equation in acidic medium

Step 1 : Assign the oxidation number to all elements in the reaction.

Oxidation Number Method

Lets take an example of unbalanced equation in acidic medium

Step 1 : Assign the oxidation number to all elements in the reaction.

Oxidation Number Method

Step 3: Find the total change in O.N. for entire molecule.

Oxidation Number Method

Step 2: Balance atoms undergoing change in O.N.

Step 5: Charge balance using H⁺ (acids) , OH^- (basic)

Oxidation Number Method

Step 6: Add H₂O to balance H & O atom

Step7: Verification:

Oxidation Number Method

• Atoms of each element
• Total Charge

Q. Balance this equation by oxidation method in basic medium

Sol.

Step 1 : Assign the oxidation number to all elements in the reaction.

Q. Balance this equation by oxidation method in basic medium

Sol.

Step 1 : Assign the oxidation number to all elements in the reaction.

Step 2: Balance atoms undergoing change in O.N.

Step 3: Find the total change in O.N. for entire molecule.

Step 5: Charge balance using OH^- (basic)

Step 6: Add H₂O to balance H & O atom

• Atoms of each element
• Total Charge

Step7: Verification:

11C08.3�PSV 1

Q. Balance the following equation in basic medium by oxidation number method.

Sol.

Step 1 : Assign the oxidation number to all elements in the reaction.

Q. Balance the following equation in basic medium by oxidation number method.

Sol.

Step 1 : Assign the oxidation number to all elements in the reaction.

Step 2: Balance atoms undergoing change in O.N.

Step 2: Balance atoms undergoing change in O.N.

Step 2: Balance atoms undergoing change in O.N.

Step 3: Find the total change in O.N. for entire molecule.

-1

+5

+2

-1

+2

-1

+2

Step 5: Charge balance using OH^- (basic)

Charge is already balanced

Step 6: Add H₂O to balance H & O atom

• Atoms of each element
• Total Charge

Step7: Verification:

11C08.3

CV 2

Half reaction Method

Lets take an example

Step-1 Separate the equation into half – reactions

Ion-electron method

Half Reaction Method

Lets take an example

Step-1 Separate the equation into half – reactions

Ion-electron method

Half Reaction Method

Half Reaction Method

Oxidation half reaction

Reduction half reaction

Step-2 Balance the atom other than O and H in each

half reaction individually.

(Fe is already balanced)

Half Reaction Method

Oxidation half reaction

Reduction half reaction

Step-3 For acidic medium, add H₂O to balance O atoms and H⁺ to balance H atoms

Half Reaction Method

Oxidation half reaction

Reduction half reaction

Step-4 Add e^- to one side of the half reaction to balance the charge

Half Reaction Method

Oxidation half reaction

Reduction half reaction

Step-5 Multiply with suitable number to equalize e^- in both half reaction

Half Reaction Method

Oxidation half reaction

Reduction half reaction

Step-6: Now add the two half reactions and cancel the e^- on each side.

Half Reaction Method

Step-7 Verification: Atoms of each element

Total Charge

Note- For reaction in basic medium.

• Firstly, follow all the steps of acidic medium.

• For each H⁺ ion , add equal no. of OH^- ion to both sides of the equation.

Q. Balance the following redox reaction in basic medium by ion-electron method.

Sol.

Step-1 Separate the equation into half – reactions

Q. Balance the following redox reaction in basic medium by ion-electron method.

Sol.

Step-1 Separate the equation into half – reactions

Step-2 Balance the atom other than O and H in each

half reaction individually.

Oxidation half reaction

Reduction half reaction

Step-2 Balance the atom other than O and H in each

half reaction individually.

Oxidation half reaction

Reduction half reaction

(Mn is already balanced)

Oxidation half reaction

Reduction half reaction

Step-3 Add H₂O to balance O atoms and H⁺ to balance H atoms

Oxidation half reaction

Reduction half reaction

Step-3 Add H₂O to balance O atoms and H⁺ to balance H atoms

Oxidation half reaction

Reduction half reaction

Step-3 Add H₂O to balance O atoms and H⁺ to balance H atoms

Oxidation half reaction

Reduction half reaction

Step-4 Add e^- to one side of the half reaction to balance the charge

Oxidation half reaction

Reduction half reaction

Step-4 Add e^- to one side of the half reaction to balance the charge

Oxidation half reaction

Reduction half reaction

Step-5 Multiply with suitable number to equalize e^- in both half reaction

Oxidation half reaction

Reduction half reaction

Step-6: Now add the two half reactions and cancel the e^- on each side.

Step-7 In basic medium, For each H⁺ ion , add equal no. of OH^- ion to both sides of the equation

Step-8 Verification: Atoms of each element

Total Charge

ConcepTest

Ready for a Challenge

Q. Balance the following redox reaction in acidic medium by ion-electron method.

Pause the video

Time duration: 2 minute

Q. Balance the following redox reaction in acidic medium by ion-electron method.

Sol.

Step-1 Separate the equation into half – reactions

Q. Balance the following redox reaction in acidic medium by ion-electron method.

Sol.

Step-1 Separate the equation into half – reactions

Step-2 Balance the atom other than O and H in each

half reaction individually.

Oxidation half reaction

Reduction half reaction

( Mn is already balanced)

( S is already balanced)

Oxidation half reaction

Reduction half reaction

Step-3 Add H₂O to balance O atoms and H⁺ to balance H atoms

Oxidation half reaction

Reduction half reaction

Step-3 Add H₂O to balance O atoms and H⁺ to balance H atoms

Oxidation half reaction

Reduction half reaction

Step-4 Add e^- to one side of the half reaction to balance the charge

Oxidation half reaction

Reduction half reaction

Step-4 Add e^- to one side of the half reaction to balance the charge

Oxidation half reaction

Reduction half reaction

Step-5 Multiply with suitable number to equalize e^- in both half reaction

Oxidation half reaction

Reduction half reaction

Step-5 Multiply with suitable number to equalize e^- in both half reaction

Oxidation half reaction

Reduction half reaction

Step-6: Now add the two half reactions and cancel the e^- on each side.

Step-7 Verification: Atoms of each element

Total Charge

Reference Questions

NCERT Exercises : 8.18, 8.19, 8.23, and 8.25

NCERT In text : 8, 9 and 10

Workbook Questions : 17 and 18

11C08.3 Balancing of Redox Reaction

11C08.4

​

Applications of Redox Reactions

11C08.4 Applications of Redox Reactions

Learning Objectives

​

Redox Reactions as the basis for Titrations

​

Electrochemical cell

​

Electrode Potential

​

​

11C08.4

​

CV 1

​

Redox Reaction as the basis for Titrations

Redox Reaction as the basis of Titration

Redox Titrations

Oxidant

Reductant

Indicator

Method to determine the strength of a reductant/oxidant using a redox sensitive indicator

Substance that changes color in response to a chemical change

Oxidizing Agents used in Redox Titration

Potassium Permanganate

End Point

Pink colour

Potassium Dichromate

Diphenylamine

/ Diphenylbenzidine

Intense blue colour

End Point

KI solution

Iodine gives an intense blue colour with starch

Starch

Sodium Thiosulphate

Starch

End Point

11C08.4

​

CV 2

​

Electrochemical Cell

Electrochemical Cell

Devices which are used to convert electrical energy into chemical energy and vice versa

Electrical energy is used to carry out a non-spontaneous redox reaction.

Chemical energy of a spontaneous redox reaction is converted into electrical energy.

Battery

Anode

Cathode

Salt Solution

Cathode

Anode

Salt Bridge

Galvanic Cell

LOAN

Left

Oxidation

Anode

Negative

Zn Anode

Cu Cathode

Voltmeter

Anode

Cathode

Salt Bridge

NaCl (aq)

Salt Bridge

Salt

Bridge

IUPAC representation of Galvanic Cell

Zn Anode

Cu Cathode

Voltmeter

Salt