Chemistry deals with various kinds of matter and changes from one matter to another. These reactions can transform the matter from one kind to another, and the vital category of such reactions is Oxidation and Reduction reactions. These reactions find extensive use in industrial, pharmaceutical, biological and agricultural areas.

These reactions are apparent from the fact that electrochemical processes for the extraction of highly reactive metals and nonmetals. The manufacturing of chemical compounds like caustic soda, operation of dry and wet batteries and corrosion of metals are within the purview of redox processes. In this article, we will look at some vital information about oxidation and reduction reactions with examples.

What are Oxidation and Reduction?

Oxidation and reduction are either defined in terms of the addition/removal of oxygen and hydrogen or in terms of gain/loss of electrons.

Oxidation	Reduction
The addition of oxygen to a substance is known as oxidation. \({\rm{2Mg + }}{{\rm{O}}_{\rm{2}}} \to {\rm{2MgO}}\) (Oxidation of \({\rm{Mg}}\) to \({\rm{MgO}}\))	The removal of oxygen from a substance is known as reduction. \({\rm{2HgO}} \to {\rm{2Hg + }}{{\rm{O}}_{\rm{2}}}\) (Reduction of \({\rm{HgO}}\) to \({\rm{Hg}}\)
The removal of hydrogen from a substance is known as oxidation. \({\rm{2}}{{\rm{H}}_{\rm{2}}}{\rm{S + }}{{\rm{O}}_{\rm{2}}} \to {\rm{2S + 2}}{{\rm{H}}_{\rm{2}}}{\rm{O}}\) (Oxidation of \({{\rm{H}}_{\rm{2}}}{\rm{S}}\) to \({\rm{S}}\))	The addition of hydrogen to a substance is known as reduction. \({\rm{C}}{{\rm{l}}_2}{\rm{ + }}{{\rm{H}}_2} \to {\rm{2HCl}}\) (Reduction of \({\rm{C}}{{\rm{l}}_{\rm{2}}}\) to \({\rm{HCl}}\))
Loss of electron from any species is known as oxidation. \({\rm{Na}} \to {\rm{N}}{{\rm{a}}^{\rm{ + }}}{\rm{ + }}{{\rm{e}}^{\rm{ – }}}\) (Oxidation of \({\rm{Na}}\) to \({\rm{N}}{{\rm{a}}^{\rm{ + }}}\)) \({{\rm{S}}^2} \to {\rm{S}} + 2{{\rm{e}}^ – }\) (Oxidation \({{\rm{S}}^{2 – }}\) to \({\rm{S}}\))	The gain of an electron by any species is known as reduction. \({\rm{F}}{{\rm{e}}^{3 + }} + {{\rm{e}}^ – } \to {\rm{F}}{{\rm{e}}^{2 + }}\) (Reduction of \({\rm{F}}{{\rm{e}}^{{\rm{3 + }}}}\) to \({\rm{F}}{{\rm{e}}^{{\rm{2 + }}}}\)) \({\rm{S + 2}}{{\rm{e}}^{\rm{ – }}} \to {{\rm{S}}^{{\rm{2–}}}}\) (Reduction of \({\rm{S}}\) to \({{\rm{S}}^{{\rm{2 – }}}}\))

Thus, the reduction process is just the opposite of the oxidation process. It is essential to know that reduction and oxidation cannot occur alone. It is because if a substance loses oxygen, there must be another substance that gains oxygen. Similarly, if a substance loses hydrogen, there must be another substance that gains hydrogen.

Thus, it is clear that if one substance is oxidised, it must reduce the other substance. It shows that both oxidation and reduction always go side by side. For this reason, these reactions are called ‘Redox Reactions’. In the word ‘Redox’, the word ‘red’ refers to reduction, and ‘ox’ refers to oxidation.

Examples of Oxidation and Reduction

Let us go into detail about this reaction with examples.

Example of Oxidation Reaction

The reaction between copper and oxygen – When copper reacts with oxygen, it forms copper oxide. In this reaction, copper gains oxygen and gets oxidised to form copper oxide. In other words, copper has been oxidised to copper oxide by the addition of oxygen. \(\mathop {{\rm{2Cu}}\left( {\rm{s}} \right)}\limits_{{\rm{Copper}}} \;{\rm{ + }}\;\mathop {{{\rm{O}}_2}\left( {\rm{g}} \right)}\limits_{{\rm{Oxygen}}} \to \mathop {{\rm{2CuO}}\left( {\rm{s}} \right)}\limits_{{\rm{Copper}}\;{\rm{oxide}}}\)

Example of Reduction Reaction

The reaction between hydrogen and copper oxide – When copper oxide reacts with hydrogen, it produces reddish-brown copper and water vapour. In this reaction, copper oxide loses oxygen and gets reduced to reddish-brown copper, whereas hydrogen gains oxygen to form water. In other words, copper oxide has been reduced to copper by losing oxygen molecules, whereas hydrogen has been oxidised to water by gaining oxygen molecules. \(\mathop {{\rm{CuO}}\left( {\rm{s}} \right)}\limits_{{\rm{Copper}}\;{\rm{oxide}}} \;{\rm{ + }}\;\mathop {{{\rm{H}}_2}\left( {\rm{g}} \right)}\limits_{{\rm{Hydrogen}}} \to \mathop {{\rm{Cu}}\left( {\rm{s}} \right)}\limits_{{\rm{Copper}}} \;{\rm{ + }}\;\mathop {{{\rm{H}}_2}{\rm{O}}\left( {\rm{g}} \right)}\limits_{{\rm{Water}}}\)

Let us now define oxidising agents and reducing agents.

The substances that lose oxygen or gain hydrogen are called oxidising agents, and the substances that lose hydrogen or gain oxygen are called reducing agents. In other words, a substance that undergoes reduction act as an oxidising agent and a substance that undergoes oxidation act as a reducing agent.

Such a reaction is called a redox reaction. These can be explained with few examples as follows:

Example 1: Reaction with copper (II) oxide and hydrogen When cupric oxide heated with hydrogen, copper metal and water formed. \({\rm{CuO\; + \;}}{{\rm{H}}_{\rm{2}}} \to {\rm{Cu\; + \;}}{{\rm{H}}_{\rm{2}}}{\rm{O}}\)

In this reaction, copper oxide \(\left( {{\rm{CuO}}} \right)\) is given oxygen and reduced to copper by reduction. Hence, \(\left( {{\rm{CuO}}} \right)\) acts as an oxidising agent. On the other hand, hydrogen \(\left( {{{\rm{H}}_{\rm{2}}}} \right)\) has gained oxygen, thereby oxidised to water by oxidation. Hence, \({{\rm{H}}_{\rm{2}}}\) acts as a reducing agent.

Thus, oxidation and reduction reactions occur simultaneously,

Example 2: Reaction between zinc oxide and carbon.

In this reaction, zinc oxide \(\left( {{\rm{ZnO}}} \right)\) has given oxygen and thereby reduced to zinc by reduction. Hence, \(\left( {{\rm{ZnO}}} \right)\) acts as an oxidising agent. On the other hand, carbon (C) has gained oxygen and converted to carbon monoxide by oxidation. Hence, carbon acts as a reducing agent.

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Example 3: Reaction between iron(III) oxide and aluminium.

In this reaction, iron oxide \(\left( {{\rm{F}}{{\rm{e}}_{\rm{2}}}{{\rm{O}}_{\rm{3}}}} \right)\) has given oxygen and thereby reduced to iron by reduction. Hence, \({\rm{F}}{{\rm{e}}_{\rm{2}}}{{\rm{O}}_{\rm{3}}}\) acts as an oxidising agent. On the other hand, aluminium \(\left( {{\rm{Al}}} \right)\) has gained oxygen, thereby oxidised to alumina \(\left( {{\rm{A}}{{\rm{l}}_{\rm{2}}}{{\rm{O}}_{\rm{3}}}} \right)\) by oxidation. Hence, aluminium acts as a reducing agent.

Example 4: Reaction between hydrogen sulphide and chlorine.

In this reaction, hydrogen sulphide \(\left( {{{\rm{H}}_{\rm{2}}}{\rm{S}}} \right)\) has given hydrogen and thereby reduced to sulphur by oxidation. Hence, \({{\rm{H}}_{\rm{2}}}{\rm{S}}\) acts as a reducing agent. On the other hand, chlorine \(\left( {{\rm{C}}{{\rm{l}}_{\rm{2}}}} \right)\) has gained hydrogen, thereby reduced to hydrogen chloride by reduction. Hence, \(\left( {{\rm{C}}{{\rm{l}}_{\rm{2}}}} \right)\) acts as an oxidising agent.

Example 5: Reaction between manganese dioxide and hydrogen chloride.

In this reaction, manganese dioxide loses oxygen and thereby gets reduced to manganese chloride. Hence, it acts as an oxidising agent. On the other hand, hydrogen chloride gains oxygen, thereby reduced to water. Hence, it acts as a reducing agent.

Effects of Oxidation Reactions In Everyday Life

There are many effects of oxidation reactions observed in our daily life. Some of them are useful, while some have undesirable results. Some of the common examples of oxidation reactions observed are:

Respiration is an oxidation reaction that takes place in our body. During respiration, food materials are oxidised to produce carbon dioxide, water, and energy.

Combustion or burning of any substance is an example of an oxidation reaction in which energy is always produced. Combustion of various fuels is a source of energy in different domestic and industrial processes.

Corrosion of active metals is also an example of oxidation reactions.
The development of foul smell and bad taste (rancidity) in fried food items is also due to oxidation when exposed to air for a long time. Let us discuss corrosion and rancidity in detail.

Corrosion

Corrosion is the slow process in which the surfaces of metallic objects are coated with oxides, hydroxide, carbonate or sulphide of the metal. It leads to the destruction of metal by chemical or electrochemical reactions with the environment. Thus, corrosion may be defined as the slow degradation of metal surfaces by the action of air, moisture or a chemical on their surface. It causes deterioration of the buildings, bridges, ships, and metal objects, especially iron. Therefore, every year we spend a tremendous amount of money on account of corrosion.

Some examples of corrosion are:

1. Development of green coating on copper
2. Tarnishing of silver
3. Rusting of iron

Corrosion of Copper

Copper articles developed a coating of green coloured copper carbonate when they were exposed to a humid atmosphere. \({\rm{2Cu}}\left( {\rm{s}} \right){\rm{ + C}}{{\rm{O}}_{\rm{2}}}\left( {\rm{g}} \right){\rm{ + }}{{\rm{O}}_{\rm{2}}}\left( {\rm{g}} \right){\rm{ + }}{{\rm{H}}_{\rm{2}}}{\rm{O}}{\left( {\rm{l}} \right)_{{\rm{From\;moist\;air}}}}{\rm{\;}} \to {\rm{CuC}}{{\rm{O}}_{\rm{3}}}{\rm{ \times Cu}}{\left( {{\rm{OH}}} \right)_{\rm{2}}}{\left( {\rm{s}} \right)_{{\rm{Basic\;Copper\;Carbonat}}{{\rm{e}}_{\left( {{\rm{Green}}} \right)}}}}\)

Corrosion of Silver

Silver articles lose their lustre and develop a black coating on their surface.
\({\rm{2Ag}}\left( {\rm{s}} \right){\rm{ + }}{{\rm{H}}_{\rm{2}}}{\rm{S}}{\left( {\rm{g}} \right)_{\left( {{\rm{From\;air}}} \right)}} \to {\rm{A}}{{\rm{g}}_{\rm{2}}}{\rm{S}}{\left( {\rm{s}} \right)_{{\rm{Silver\;sulphide}}}}_{\left( {{\rm{Black}}} \right)}{\rm{ + }}{{\rm{H}}_{\rm{2}}}\left( {\rm{g}} \right)\)

Corrosion of Iron (Rusting)

Iron articles develop a coating of a reddish-brown flaky powder when left open in moist air for a long time. The reddish-brown flaky powder formed is a chemically hydrated ferric oxide known as rust, and the phenomenon is known as rusting of iron.
\({\rm{2Fe}}\left( {\rm{s}} \right){\rm{ + }}\frac{{\rm{3}}}{{\rm{2}}}{{\rm{O}}_{\rm{2}}}\left( {\rm{g}} \right){\rm{ + x}}{{\rm{H}}_{\rm{2}}}{\rm{O}} \to {\rm{F}}{{\rm{e}}_{\rm{2}}}{{\rm{O}}_{\rm{3}}}{\rm{ \times x}}{{\rm{H}}_{\rm{2}}}{{\rm{O}}_{{\rm{Hydrated\;Ferric\;oxide}}}}_{\left( {{\rm{Rust}}} \right)}\)

Rancidity It has been observed many times that the fat/oil containing food materials undergo an unpleasant change in flavour and odour when exposed to air for a long time. Rancidity is a general term given to this phenomenon.

Rancidity is the aerial oxidation of fat/oil containing food materials indicated by unpleasant smell and taste. It is an undesirable phenomenon that causes the spoilage of food and makes it unsafe for consumption.

Prevention of Rancidity

1. The use of antioxidants retards the oxidation of oil or fat present in food. The typical antioxidants are BHA (Butylated hydroxyanisole) and BHT (Butylated hydroxytoluene).
2. Packing in Nitrogen: In some packed foodstuff, such as potato chips, the plastic bags are filled with unreactive gas nitrogen so that no air or oxygen is available to bring about the oxidation of food and make it rancid.
3. Storing the food at low temperature also retards rancidity. Thus, keeping food in the refrigerator is also a method of prevention/retardation of rancidity.
4. Storing the food materials in air-tight containers also helps to slow down rancidity.
5. Keeping food away from sunlight also retards the process of rancidity.

Summary

Oxidation and reduction are either defined in terms of the addition/removal of oxygen and hydrogen or in terms of gain/loss of electrons. Where there is reduction, there is always oxidation. So, in this article, we learnt about oxidation and reduction reactions with examples and the effects of oxidation in our daily life. We also learnt about real-life applications of reduction and oxidation reactions and their usefulness. Finally, we answered some frequently asked questions on this topic.

Frequently Asked Questions (FAQs) on Oxidation and Reduction

The most commonly asked questions about Oxidation and Reduction are answered here:

Q.1. Oil and fat-containing food items flushed with nitrogen. Why? Ans: Nitrogen is a chemically unreactive gas that prevents the oxidation of food. Therefore, oil and fat containing food items are flushed with nitrogen to prevent them from getting oxidised. “We hope this article on ‘Oxidation and Reduction’ has helped you. If you have any queries, drop a comment below, and we will get back to you.”

Q.2. Explain oxidation in terms of gain or loss of oxygen with an example.Ans: A process that involves a gain of oxygen is called oxidation. Example: Reaction between copper with oxygen. When copper reacts with oxygen, it forms copper oxide. \({\rm{2Cu}}\left( {\rm{s}} \right){\rm{ + }}{{\rm{O}}_{\rm{2}}}\left( {\rm{g}}\right) \to {\rm{2CuO}}\left( {\rm{s}} \right)\) In this reaction, copper gains oxygen and gets oxidised to form copper oxide. In other words, copper has been oxidised to copper oxide by the addition of oxygen.

Q.3. Identify the substances that are oxidised and the substances that are reduced in the following reactions: (a) \({\rm{4Na}}\left( {\rm{s}} \right){\rm{ + }}{{\rm{O}}_{\rm{2}}}\left( {\rm{g}} \right) \to {\rm{2N}}{{\rm{a}}_{\rm{2}}}{\rm{O}}\left( {\rm{s}} \right)\) (b) \({\rm{CuO}}\left( {\rm{s}} \right){\rm{ + }}{{\rm{H}}_{\rm{2}}}\left( {\rm{g}} \right){\rm{\;}} \to {\rm{Cu}}\left( {\rm{s}} \right){\rm{ + }}{{\rm{H}}_{\rm{2}}}{\rm{O}}\left( {\rm{l}} \right)\) Ans: (a) In this reaction, sodium \(\left( {{\rm{Na}}} \right)\) gains oxygen and hence oxidised to sodium oxide \(\left( {{\rm{N}}{{\rm{a}}_{\rm{2}}}{\rm{O}}} \right){\rm{.}}\) Consequently, oxygen \(\left( {{{\rm{O}}_{\rm{2}}}} \right)\) is reduced. (b) In this reaction, hydrogen \(\left( {{{\rm{H}}_{\rm{2}}}} \right)\) gains oxygen and forms water \(\left( {{{\rm{H}}_{\rm{2}}}{\rm{O}}} \right){\rm{.}}\) Hence it is oxidised. On the other hand, copper (II) oxide \(\left( {{\rm{CuO}}} \right)\) loses oxygen and is therefore reduced to copper \(\left( {{\rm{Cu}}} \right){\rm{.}}\)

Q.4. Explain reduction in terms of gain or loss of oxygen with an example.Ans: A process that involves the loss of oxygen is called reduction. Example: Reaction between hydrogen and copper oxide. When copper oxide reacts with hydrogen, it produces reddish-brown copper and water vapour. \({\rm{CuO}}\left( {\rm{s}} \right){\rm{ + }}{{\rm{H}}_{\rm{2}}}\left( {\rm{g}} \right) \to {\rm{Cu}}\left( {\rm{s}} \right){\rm{ + }}{{\rm{H}}_{\rm{2}}}{\rm{O}}\left( {\rm{g}} \right)\) In this reaction, copper oxide loses oxygen and gets reduced to reddish-brown copper, whereas hydrogen gains oxygen to form water. In other words, copper oxide has been reduced to copper by losing oxygen molecules, whereas hydrogen has been oxidised to water by gaining oxygen molecules.

Q.5. What is oxidation and reduction reaction? Explain with an example?Ans: Oxidation is defined as (i) The addition of oxygen to an element or compound or (ii) The removal of hydrogen from a compound. Example, Calcium and oxygen combine to form calcium oxide. \({\rm{2Ca\; + \;}}{{\rm{O}}_{\rm{2}}} \to {\rm{2CaO\;}}\) Here, oxygen is added to calcium. Hence, this is oxidation. Reduction is defined as (i) The addition of hydrogen to an element or compound or (ii) The removal of oxygen from a compound. Example, Reduction of \({\rm{HgO}}\) to \({\rm{Hg}}\) \({\rm{2HgO}} \to {\rm{2Hg + }}{{\rm{O}}_{\rm{2}}}\)

Q.6. Explain one example of each of the following: (a) A redox reaction which is also a combination reaction. (b) A redox reaction which is also a displacement reaction. Ans: (a) \({\rm{2Mg}}\left( {\rm{s}} \right){\rm{ + }}{{\rm{O}}_{\rm{2}}}\left( {\rm{g}} \right) \to {\rm{2MgO}}\left( {\rm{s}} \right)\) The above reaction is a redox reaction as well as a combination reaction. (b) \({\rm{CuO + Zn}} \to {\rm{ZnO + Cu}}\) The above reaction is a redox reaction as well as a displacement reaction.

We hope that you have read this article on Oxidation and Reduction and understood the concept by now. In case, you have any queries or suggestions, feel to write to us by commenting below.