Redox Reaction

What is Redox Reaction

Many chemical reactions involve transfer of electrons from one chemical substance to another. These electron transfer reactions are termed as oxidation-reduction or Redox reaction, or those reactions which involve oxidation and reduction both simultaneously are known as oxidation and reduction/ Redox reaction. Redox reaction can also be termed as an increase in oxidation number or decrease in oxidation number simultaneously.

Oxidation and Reduction

There are mainly four four concepts of oxidation and reduction reaction:

A. Classical Concept: According to this concept, oxidation and reduction can be explained as:

1. Oxidation

Oxidation is a process which involves:

Addition of oxygen

Removal of hydrogen

Addition of electronegative elements

Removal of electropositive elements

Increment in oxidation state of electropositive element.

2. Reduction

Reduction is a process which involves:

Removal of oxygen

Addition of hydrogen

Removal of electronegative elements

Addition of electropositive elements

Decrement in oxidation state of electropositive elements

B. Modern Concept or Electronic Concept

1. Oxidation

According to this concept the process which involves the loss of one or more electrons from an atom or an ion or molecules is called oxidation.

2. Reduction

According to this concept, the process which involves gain of one or more electrons by an atom or ion molecule is called reduction.

C. Valency Concept of Oxidation and Reduction

1. Oxidation 

According to this concept, it is the process in which increase in positive valency or decrease in negative valency of a substance takes place called oxidation.

2. Reduction

According to this concept,it is the process in which decrease in positive or increase in negative charge of a substance takes place called reduction.

D. Oxidation Number Concept

1. Oxidation

According to this concept, the oxidation number of elements increases.

2. Reduction

According to this concept oxidation number of elements decreases.

Oxidising Agent or Oxidants

The Substance which accept electrons in a chemical reaction i.e electron acceptors are oxidising agents:

1. Oxidising agents are lewis acid.

2. Substance which can oxidise others and reduce themselves.

3. Substance which shows decrement in oxidation number.

4. All high electronegative elements like N, O, F, Cl, etc are oxidants.

5. All metallic oxides are oxidants.

6. Some non metallic oxides are also oxidants like CO₂, CaO, etc.

Reducing Agents or Reductant

The substances which donate electrons in a chemical reaction are reducing agents i.e electron donors are reducing agents.

1. Reducing agents are Lewis base.

2. Substances which can reduce others and oxidise themselves.

3. Substance which shows decrement in oxidation number.

4. All metal like K, Mg, Ca, etc are examples of reductants.

5. All metallic hydrides are examples of reductants.

6. All hydro acids are reductants. Example: HF, HCl, HBr, etc.

Oxidation Number

It represents the number of electrons gained or lost by an atom when it changes in compound from free state. It is also defined as charge on an atom when the atom is in combining state.

1. If electrons are gained by an atom in the formation of compounds the oxidation number is given a negative sign.

2. If electrons are loose by atom in the formation of compounds the oxidation number is given a positive sign.

3. It represents real charge in case of ionic compounds and imaginary charge in case of covalent compounds.

4. Maximum oxidation number is equal to the group number in the periodic table.

5. Minimum number of oxidation states is equal to group number i.e (-8).

Oxidation State

Oxidation state of an atom is defined as the oxidation number per atom for all practical purposes. Oxidation state is often expressed as the oxidation number.

Types of Redox Reactions

1. Intermolecular Redox Reaction 

When oxidation and reduction take place separately in the different compounds called intermolecular redox reactions.

SnCl₂+ 2FeCl₃-------SnCl₄+2FeCl₂

2. Intramolecular Redox Reaction

During chemical reaction if oxidation and reduction take place in a single compound then reaction is called intramolecular redox reaction.

2KClO₃------KCl+3O₂

3. Disproportionation Reaction

When reduction and oxidation take place on the same elements of the compound is called disproportionation reaction.

H₂O₂--------H₂O+3O₂

Multiple Choice Questions

1. Oxidation number of nitrogen in NH₂OH:

1. 0

2. +1

3. -1

4. -2

      Answer: (C)

2. Which one has same oxidation state in all of its compound:

1. Hydrogen

2. Fluorine

3. Carbon

4. Oxygen

      Answer: (b)

    3. Oxidation number of C in HCN:

1. +2

2. -3

3. +3

4. Zero

      Answer: (a)

   4. If elements is in lowest oxidation state under proper condition it act as a:

1. Reducing agent

2. An Oxidising agent

3. Both of them

4. None of them

      Answer: (a)