Question

How is aluminium metal extracted? Explain with the help of an equation.

Answer 1

Aluminium metal is obtained through the electrolytic reduction of molten aluminium oxide. When electric current is applied to molten aluminium oxide, it decomposes into aluminium metal and oxygen gas.

\[\ce{\underset{(Molten)}{\underset{Aluminium oxide}{2Al2O3_{(l)}}} ->[Electrolysis] \underset{Aluminium metal}{4Al_{(l)}} + \underset{Oxygen}{3O2_{(g)}}}\]

Molten aluminium oxide (Al₂O₃) comprises free aluminium ions (Al³⁺) and free oxide ions (O²⁻). In the electrolysis of molten aluminium oxide, the subsequent reactions occur at the two electrodes.

The positively charged aluminium ions (Al³⁺) are drawn to the cathode (negative electrode). The aluminium ions receive electrons from the cathode and are reduced to generate aluminium atoms (or aluminium metal).

At cathode: \[\ce{\underset{(Free molten Al2O3)}{\underset{Aluminium ion}{Al^3+}} + \underset{(From cathode)}{\underset{Electrons}{3e-}} -> \underset{(Aluminium metal)}{\underset{Aluminium atom}{Al}}}\]

Thus, aluminium metal is formed at the cathode.

The negatively charged oxide ions (O²⁻) are drawn to the anode (positive electrode). The oxide ions donate electrons to the anode and undergo oxidation to produce oxygen gas.

At anode: \[\ce{\underset{(Free molten Al2O3)}{\underset{Oxide ions}{2O^2-}} + \underset{(Given to anode)}{\underset{Electrons}{4e-}} -> \underset{Oxygen gas}{O2}}\]

Thus, oxygen gas is produced at the anode.