Question

What is electrolytic reduction? Explain with the help of an example.

Answer 1

Electrolytic reduction is the process through which various cations are deposited at an electrode and some gases are liberated at the opposite electrode. This process is used for segregating the ions of an ionic compound.

Complete answer:
Reduction is a phenomenon that involves a gain or acceptance of electrons by a chemical species.
An ionic compound contains both cations and anions bonded to each other through strong electrostatic forces of attraction. These ions cannot be separated by simply heating the compound that may lead to its decomposition but not dissociation. Dissociation of ions can be observed in aqueous solutions where the high hydration enthalpy is sufficient to keep the ions apart.
In the molten state, the ions are mobile and can be segregated by applying external electrical forces. This process of segregation of oppositely charged ions in their solution or molten state is called electrolysis.
An electrolytic circuit consists of a negatively charged electrode (cathode) and a positively charged electrode (anode) that are dipped in the solution or molten compound. When electricity is passed through the circuit, the cations migrate towards the cathode and the anions migrate towards the anode.
The metal ions coming in contact with the cathode accept the electrons from it and get reduced in the process. This electricity induced reduction is known as electrolytic reduction. The metal cation upon getting gets deposited as solid metal on the cathode itself.
An example of electrolytic reduction is :
${\text{At cathode: }}A{l^{3 + }} + 3{e^ - } \to Al(s)$
Deposition of aluminium metal is observed on the cathode when molten aluminium oxide $A{l_{_2}}{O_3}$ is electrolytically reduced.

Note:
Cathode and anodes do not have a fixed charge and change according to the cell in which they are used. In an electrolytic circuit, the cathode is negatively charged and the anode is positively charged but in a galvanic cell the polarity of the electrodes is reversed.