Question

What is a redox couple?

Answer 1

Hint: A chemical reaction in which reduction and oxidation of elements takes place simultaneously, is known as a redox reaction. The compound which itself gets oxidized to reduce other compounds in the reaction is known as reducing agent whereas the compound which itself gets reduced to oxidize other compounds in the reaction is known as oxidizing agent.

Complete answer:
In a redox reaction, when oxidizing and reducing agents appear to be on opposite sides of the half reaction, then they are termed as a redox couple. These are analogous to conjugate acid-base pair i.e., for every reducing agent, there corresponds an oxidizing agent and for every oxidizing agent, there corresponds a reducing agent.
In a redox couple, the stronger an oxidizing agent, the weaker will its corresponding reducing agent and the stronger a reducing agent, the weaker will be its corresponding oxidizing agent. A redox couple is denoted by ${\text{Ox|Red}}$i.e., the ion with higher oxidation number will be written before the ion with lower oxidation number.
Let us consider an example of redox couple in a redox reaction as follows:
$C{e^{4 + }} + S{n^{2 + }} \to C{e^{3 + }} + S{n^{4 + }}$
For the given redox reaction, oxidation half reaction and reduction half reaction can be written as follows:
Reduction half reaction: $C{e^{4 + }} + e \to C{e^{3 + }}$
Oxidation half reaction: $S{n^{2 + }} \to S{n^{4 + }} + e$
In the respective half reactions, $C{e^{4 + }}|C{e^{3 + }}$ and $S{n^{4 + }}|S{n^{2 + }}$ are formed jointly on the opposite sides of the reaction. Hence, these are considered as a redox couple for the given redox reaction.

Note:
Conjugate acid-base pair: It is a pair of compounds which differ only in one proton i.e., an acid which has a tendency to donate a proton and a base which has a tendency to accept a proton, together forms a conjugate acid-base pair. The Redox couple is similar to the conjugate acid-base pair.