Question

Write an equation for the reaction that takes place at the anode during the extraction of aluminium by the electrolytic process?

Answer 1

The electrolytic process involves the electrolytic dissociation of the compound into its constituents ions i.e. cation and anion by passing the electric current.

1) During the extraction of aluminum, the iron tank lined inside with graphite acts as a cathode.

2) A bunch of graphite rods in the molten electrolyte act as the anode.

Electrolysis of alumina:

Alumina will undergo electrolysis and gives aluminum cation and oxide anion.

$$\begin{gathered} {\mathrm{Al}}_2{\mathrm{O}}_3\left(\mathrm{aq}\right)\to 2{\mathrm{Al}}^{3+}\left(\mathrm{aq}\right)+3{\mathrm{O}}^{2-}\left(\mathrm{aq}\right) \\ \mathrm{Alumina}\mathrm{aluminium}\mathrm{ion}\mathrm{oxide}\mathrm{ion} \\ \mathrm{cation}\mathrm{anion} \end{gathered}$$

Reaction at the anode:

• The anode is a positive terminal that attracts negative ions and loses electrons.

$$\begin{gathered} 6{\mathrm{O}}^{2-}\left(\mathrm{aq}\right)-12{\mathrm{e}}^{-}\to 6\left[\mathrm{O}\right]\left(\mathrm{g}\right) \\ 3\mathrm{O}\left(\mathrm{g}\right)+3\mathrm{O}\left(\mathrm{g}\right)\to 3{\mathrm{O}}_2\left(\mathrm{g}\right) \end{gathered}$$

• The oxygen gas evolved at the anode reacts with graphite anodes and forms carbon monoxide $\left(\mathrm{CO}\right)$ which further forms carbon dioxide $\left({\mathrm{CO}}_2\right)$.

$$\begin{gathered} 2\mathrm{C}\left(\mathrm{s}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)\to 2\mathrm{CO}\left(\mathrm{g}\right) \\ 2\mathrm{CO}\left(\mathrm{g}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)\to 2{\mathrm{CO}}_2\left(\mathrm{g}\right) \end{gathered}$$