Concept of Oxidation and Reduction

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Introduction 

Oxidation occurs in a chemical reaction when there is a loss of electrons and a gain of Oxygen. On the other hand, reduction happens in a reaction when there is a gain of electrons and a loss of Oxygen.

In simple words, Oxidation is the addition of Oxygen, whereas reduction is the loss of Oxygen in a reaction.

Oxidation and reduction occur simultaneously in a chemical reaction. One element loses the electron while the other gains it. Such reactions are called oxidation-reduction reactions or Redox reactions.

Oxidation 

Oxidation can be defined as a loss of electrons or hydrogen and gain of Oxygen. Oxidation reaction happens when an atom or compound loses one or more than one electron.

Some elements like sodium, magnesium and iron lose electrons more quickly than others. They are called easily oxidised compounds.

In the case of oxidation following happens:

•   Addition of Oxygen or electronegative element
•   Loss of hydrogen or electropositive element
•   Increase in positive charge
•   Decrease in negative charge

Examples of oxidation reactions

2 MgO + O2 → 2 MgO (addition of oxygen)

FeCl2 + 3/2Cl2 → FeCl2 (addition of electronegative element)

H2S + Cl2 → HCl + S (removal of hydrogen)

Hg2Cl2 → HgCl2 + Hg (removal of electropositive element)

How does Oxidation take place?

Upon Oxidation, the properties of an atom or compound change. To understand the oxidation reaction, let us take an example of the Oxidation of iron.

Unoxidised iron is strong and durable. However, oxidised or rusted iron loses strength. Iron objects undergo Oxidation when they come in contact with water molecules that carry Oxygen. Upon Oxidation of iron, a reddish brittle substance is formed on the surface of the iron object. This substance is called rust, and the oxidation process of iron is called rusting.

Pure unoxidized iron has three electrons. Iron is an easily oxidised compound that loses all three electrons upon Oxidation. After the Oxidation, iron is left with only a positive charge of three.

This is how an oxidation reaction loses negative charge and gains positive charge. Also, it loses electrons and gains Oxygen.

4 Fe + 3 O2 → 2 Fe2O

As you can see in the chemical reaction above, iron combines with oxygen to form Iron oxide, Fe2O.

Reduction 

A reduction reaction can be defined as the process of gaining electrons or losing Oxygen. Reduction reactions occur when a compound gains one or more electrons or loses Oxygen.

In the reduction reaction following happens:

•   Addition of hydrogen or electropositive element
•   Loss of Oxygen or electronegative element
•   Decrease in positive charge
•   Increase in negative charge

Examples of the reduction reaction

NH3 + HCl  →  NH4Cl (addition of hydrogen)

2 Na + H2O →  2 NaOH (addition of electropositive element)

2 KClO3 → 2 KCl + 3 Cl2 (removal of oxygen)

H2S → H2 + S (removal of electronegative element)

Understanding Redox Reaction

Oxidation and reduction reactions most of the time co-exists in a reaction. Together it is called oxidation-reduction reaction or Redox reaction.

In the redox reaction, one atom or compound being oxidised loses electrons while the other atom undergoing reduction gains electrons. In other words, a compound or atom steals the electrons from another compound to undergo reduction.

In simple words, there is a transfer of electrons or charge from one compound to another in a Redox reaction.

Oxidation is always coupled with reduction. One compound is oxidised, and it loses electrons to the other compound that gains those electrons and gets reduced in the process.

The compound that gains electrons acts as an oxidising agent, while the compound that loses electrons acts as the reducing agent.

What is an Oxidizing Agent?

•   An oxidising agent is also called an oxidant
•   The chemical substance or atom or compound that oxidises others or steals electrons from others to get reduced is called an oxidising agent
•   The oxidant accepts electrons and decreases its oxidation number

What is a Reducing Agent?

•   The chemical substance or atom or compound that reduces others by losing electrons and getting oxidised are called a reducing agent
•   Reducing agent is also known as reductant
•   The reductant gives electrons and increases its oxidation number

Understanding Redox reaction with an example

Rusting is a classic example of a redox reaction. Oxygen steals electrons from iron when it rusts. While Oxygen is reduced, iron is oxidised. The result is iron oxide, also known as rust. The unoxidised or pure form of iron is distinct from the oxidised form found in rust.

In a simple redox process, the following equation illustrates an evident example of oxygen transfer:

CuO + Mg → Cu + MgO  ………………..(1)

Ionic compounds include copper(II) oxide and magnesium oxide. If you write the above as an ionic equation, you’ll notice that the oxide ions are spectator ions.

Magnesium decreases the copper(II) ion in the preceding reaction by transferring electrons and neutralising its charge. As a result, magnesium acts as a reducing agent. Another way to phrase it is that the copper(II) ion removes electrons from the magnesium ion, resulting in the formation of a magnesium ion. The copper(II) ion functions as an oxidiser.

Redox Reaction and Oxidation Number

In the oxidation process, there is an increase in the oxidation number. While in reduction, there is a decrease in the oxidation number.

•   An increase in oxidation number means loss of electrons
•   Decrease in oxidation number means a gain of electrons

Consider the reaction that follows.

CO2(g) + H2O(g) = CO2(g) + H2O(g) (g)

In this reaction, the total number of electrons in each atom’s valence shell remains constant, as seen in the diagram below.

The oxidation status of these atoms changes during this process. Carbon’s oxidation state grows from +2 to +4, while hydrogen’s oxidation state declines from +1 to 0.

Therefore when an atom’s oxidation number increases, it is oxidised. When an atom’s oxidation number decreases, it is reduced.

Conclusion

Oxidation and reduction reaction when taken place simultaneously , is also known as Redox reaction.

It can be confusing how Oxidation and reduction takes place and who loses or gains electrons. Our comprehensive guide will help you clear the concept of oxidation and reduction.