Question

Name the process by which $\mathrm{Al}$ is obtained from purified bauxite.

Answer 1

• The process in which $\mathrm{Al}$ is obtained from purified bauxite is Hall's process by electrolysis.
• During electrolysis, alumina decomposed into its constituent ions i.e. aluminium and oxide ions.

$2{\mathrm{Al}}_2{\mathrm{O}}_3\left(\mathrm{aq}\right)\stackrel{\mathrm{Electrolysis}}{\to }4{\mathrm{Al}}^{3+}\left(\mathrm{aq}\right)+6{\mathrm{O}}^{2-}\left(\mathrm{aq}\right)$

• At the cathode, aluminium ions undergo oxidation to give aluminium atoms.

$4{\mathrm{Al}}^{3+}\left(\mathrm{aq}\right)+12{\mathrm{e}}^{-}\to 4\mathrm{Al}\left(\mathrm{s}\right)$

• At the anode, the oxide ion undergoes reduction to evolved oxygen.

$6{\mathrm{O}}^{2-}\left(\mathrm{aq}\right)-12{\mathrm{e}}^{-}\to 3{\mathrm{O}}_2\left(\mathrm{g}\right)$

• In Hall-Heroult's process, pure ${\mathrm{Al}}_2{\mathrm{O}}_3$ is mixed with ${\mathrm{CaF}}_2$ or ${\mathrm{Na}}_3{\mathrm{AlF}}_6$ which lowers the melting point of the mixture and enhances conductivity.

Hence, $\mathbf{Al}$ is obtained from purified bauxite by Hall-Heroult's process.