Question

Identify the reducing agent and oxidizing agent in the following reactions:

$4{\mathrm{NH}}_3+5{\mathrm{O}}_2\to 4\mathrm{NO}+6{\mathrm{H}}_2\mathrm{O}$

Answer 1

1. Redox reactions

A reaction between two reactants in which one of the reactants get oxidized and the other gets reduced is called a redox reaction. The reactant getting reduced is called the oxidizing agent as it accepts electrons and aids the oxidation of another reactant. Similarly, the reactant that gets oxidized is called the reducing agent.

The oxidizing agent and the reducing agent of a reaction can be identified by the change in the oxidation state of the reactants. Oxidation causes an increase in the oxidation state of the species and reduction causes a decrease in the oxidation state.

2. Identifying the oxidizing and reducing agents

$$\begin{gathered} 4{\mathrm{NH}}_3\left(\mathrm{g}\right)+5{\mathrm{O}}_2\left(\mathrm{g}\right)\to 4\mathrm{NO}\left(\mathrm{g}\right)+6{\mathrm{H}}_2\mathrm{O}\left(\mathrm{g}\right) \\ \mathrm{Ammonia}\mathrm{Oxygen}\mathrm{Nitric}\mathrm{oxide}\mathrm{Water} \end{gathered}$$

In the above equation, the oxidation state of Oxygen decreases from 0 in Oxygen to -2 in Water $\left({\mathrm{H}}_2\mathrm{O}\right)$. Therefore, oxygen undergoes reduction.

Also, the oxidation state of Nitrogen increases from -3 in Ammonia to +2 in Nitric oxide. Therefore, it undergoes oxidation.

Thus, Ammonia $\left({\mathrm{NH}}_3\right)$ is a reducing agent and Oxygen $\left({\mathrm{O}}_2\right)$ is an oxidizing agent.