Question

Define oxidising and reducing agents.

Answer 1

1. Oxidising agent

Definition:

An oxidising agent is an agent which causes the oxidation of others and themselves get reduced by gaining electrons or by giving oxygen.

The one who gets reduced acts as an oxidising agent.

Example:

$2{\mathrm{H}}_2\left(\mathrm{g}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)\to 2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)$

Hydrogen Oxygen Water

• Here oxidation state of $\mathrm{H}$ in ${\mathrm{H}}_2$ is $0$and that of $\mathrm{O}$ in ${\mathrm{O}}_2$ is $0$ at the reactant side but the oxidation state of $\mathrm{H}$ in ${\mathrm{H}}_2\mathrm{O}$ is $+1$ and that of $\mathrm{O}$ in ${\mathrm{H}}_2\mathrm{O}$ is $-2$ at the product side.
• So, we can say that ${\mathrm{H}}_2$ is getting oxidised since its oxidation number is increasing from $0$ to $+1$ and ${\mathrm{O}}_2$ is getting reduced since its oxidation number is decreasing from $0$ to $-2$.
• The one who gets oxidised acts as a reducing agent and the one who gets reduced acts as an oxidising agent.
• So here ${\mathrm{H}}_2$ is a reducing agent and ${\mathrm{O}}_2$ is an oxidising agent.

2. Reducing agent

Definition:

Reducing agent is an agent which causes the reduction of others and themselves get oxidised by donating electrons or by gaining oxygen.

The ones that get oxidised act as a reducing agent.

Example:

${\mathrm{H}}_2\left(\mathrm{g}\right)+{\mathrm{F}}_2\left(\mathrm{g}\right)\to 2\mathrm{HF}\left(\mathrm{g}\right)$

Hydrogen Fluorine Hydrogen fluoride

• Here oxidation state of $\mathrm{H}$ in ${\mathrm{H}}_2$ is $0$ and that of $\mathrm{F}$ in ${\mathrm{F}}_2$ is $0$ at the reactant side but the oxidation state of $\mathrm{H}$ in $\mathrm{HF}$ is $+1$ and that of $\mathrm{F}$ in $\mathrm{HF}$ is $-1$ at the product side.
• So, we can say that ${\mathrm{H}}_2$ is getting oxidised since its oxidation number is increasing from $0$ to $+1$ and ${\mathrm{F}}_2$ is getting reduced since its oxidation number is decreasing from $0$ to $-1$.
• The one who gets oxidised acts as a reducing agent and the one who gets reduced acts as an oxidising agent.
• So here ${\mathrm{H}}_2$ is a reducing agent and ${\mathrm{F}}_2$is an oxidising agent.