Reducing Agent in Redox Reactions

Before understanding what reducing agents are, you need to know what reduction and oxidation is? Generally, students get confused in redox reactions aboout  which element is getting reduced and which is getting oxidized. So, we are explaining oxidation and reduction first in brief here. 

What is Oxidation and Reduction? 

Reduction is loss of oxygen atoms and gain of electrons and hydrogen. While oxidation is gain of oxygen and loss of electrons and hydrogen. Thus, we can say when an element gets oxidized, its oxidation state increases while in reduction it decreases. Same thing is explained in concise way in the table given below –

The reactions in which oxidation and reduction both take place are called redox reactions. 

Examples of Oxidation and Reduction –

• Reaction of copper with silver nitrate is an example of redox reaction. The reaction is given below showing oxidation and reduction.  

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• Reaction between magnesium and oxygen is an example of a redox reaction. The reaction is given below showing oxidation and reduction.

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• Reaction between iron and oxygen. 

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• Reaction between iron oxide and carbon monoxide. 

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• Reaction of copper oxide with hydrogen.

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• Reaction of iron oxide with hydrogen.

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What is a Reducing Agent? 

Reducing agent is an element (or compound) that –

• Loses its electron/s to an electron recipient group and

• It Itself gets oxidized in a redox chemical reaction. 

Let’s understand it by an example of redox reaction

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In the above reaction iron is losing 2 electrons thus, acting as a reducing agent. Oxidation state of iron as a reactant is 0 while +2 as a product in the reaction. Thus, the oxidation state of iron is increasing, so oxidation is taking place. While another reactant copper is gaining two electrons and working as an oxidizing agent. The oxidation state of copper is +2 as reactant in the reaction while 0 as product so reduction is taking place. Thus, iron is acting as a reducing agent but getting oxidized itself while copper is acting as an oxidizing agent but reduced.  

Examples of Reducing Agents 

Following are the common reducing agents – 

• Sodium borohydride 

• Zinc amalgam 

• Lithium aluminum hydride (LiAlH4)

• Diborane 

• Sodium amalgam 

• Sodium lead alloy 

• Nascent hydrogen 

• Thiosulfates 

• Oxalic acid

• Formic acid 

Characteristics of reducing Agent

• Reducing agents have a tendency to give away electrons. The metals of the s-block in the periodic table are stated to be top reducing agents.

• The reducing agent after losing electrons gets oxidized and also causes the other reactant to get reduced via providing electrons.

• All of the correct reducing agents have the atoms which have low electronegativity and a good capacity of an atom or a molecule to attract the bonding electrons and the species having very small ionization energies.

• All the oxidation and reduction reactions contain the transfer of electrons.

• While a few substances are oxidized, it is said to lose electrons and the substance which gets electrons is stated to be reduced.

• If the substance has a strong tendency to lose electrons, then it is said to be a strong reducing agent (because it will reduce the opposite substances through donating electrons).

Reducing Agents in Redox Reactions

Some examples of redox reactions are given below in which reducing and oxidizing agents have been shown for your better understanding –

• Reaction of Zinc and Copper – 

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• Reaction of Ammonia and Oxygen – 

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• Reaction of Copper Sulfate with Zinc – 

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As you can see, the oxidation state of zinc is increasing so it's getting oxidized. Thus, zinc is working as a reducing agent in the above reaction. While copper sulfate is working as an oxidizing agent as the oxidation state of copper is decreasing. 

• Reaction of Hydrogen Sulfide with Chlorine – Image will be uploaded soon.

As oxidation state of sulfur is increasing (-2 🡪 0) so it is working as reducing agent in the reaction while oxidation state of chlorine is decreasing so it is working as oxidizing agent. 

Strong and Weak Reducing Agents 

Strong reducing agents are electropositive elements which can lose electrons easily in the chemical reactions. Strong reducing agents are weak oxidizing agents. Sodium, hydrogen, and lithium are examples of strong oxidizing agents. While weak reducing agents cannot lose electrons easily. Fluorine, chlorine, iron etc. are weak reducing agents. We can know the strength of reducing agents by electrochemical series as well. As we move upwards from hydrogen in the electrochemical series then the strength of reducing agents decreases. While if we move downwards from hydrogen then the strength of reducing agents increases. 

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Conclusion:

Reducing agents reduces others while itself gets oxidized by losing electrons. As reducing agents lose electrons so generally, they possess low electronegativity and very small ionization energies. S-block metals generally work as good reducing agents. It is also called reductant or reducers. You can understand more about reducing agents through this article and better know the concepts through the given examples.