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

Electrolytic reduction is a chemical process that involves the use of an electric current to drive a non-spontaneous reduction reaction. It is typically employed to extract metals from their ores or to obtain pure metals from their compounds.

In an electrolytic reduction, an electrolyte is used, which is a substance that can conduct electricity when dissolved or molten. The electrolyte contains ions of the metal that is to be reduced. Two electrodes, an anode (positive electrode) and a cathode (negative electrode), are immersed in the electrolyte. The anode attracts negatively charged ions (anions) and the cathode attracts positively charged ions (cations).

When an electric current is applied, positive ions are attracted towards the cathode, where they gain electrons and undergo reduction. The reduction reaction causes the metal ions to be reduced to their elemental form, which deposits on the cathode. At the anode, negatively charged ions are oxidized, releasing electrons to maintain the current flow.

Let's take the example of the electrolytic reduction of molten aluminum oxide (Al2O3) to obtain aluminum metal. In this process, a mixture of alumina (Al2O3) and cryolite (Na3AlF6) is used as the electrolyte. The mixture is molten at high temperatures.

The cathode is made of graphite, which is an excellent conductor of electricity and resistant to the high temperatures involved. The anode is typically made of carbon, which reacts with the oxygen produced during the electrolysis, forming carbon dioxide.

When a direct current is applied, aluminum cations (Al3+) in the molten electrolyte are attracted to the cathode. At the cathode, each aluminum ion gains three electrons and undergoes reduction, resulting in the formation of aluminum metal:

Al3+ + 3e- → Al

The aluminum metal is then collected at the bottom of the cell, while oxygen gas is liberated at the anode:

2O2- → O2 + 4e-

Overall, the electrolytic reduction of molten aluminum oxide allows the extraction of aluminum metal, which can be further purified and used for various applications.

It's important to note that electrolytic reduction requires a significant amount of energy input because it involves driving a non-spontaneous reaction. However, it is often chosen for processes where alternative methods, such as thermal reduction, are not feasible or economical.