Name: Metal Displacement Reactions
Uploaded: 2019-07-19
Duration: 9 min 12 s
Description: This video describes the displacement reactions based on the reactivity series in which a more reactive element displaces a less reactive one from its aqueou...

Question

Explain the electrochemical reduction method to obtain aluminium from alumina with diagram.

Accepted Answer

Electrolysis of alumina is carried out in an electrolytic cell at a much lower temperature by dissolving it in molten cryolite $({Na}_{3} {AlF}_{6})$ and fluorspar $({CaF}_{2})$ . The addition of cryolite, and fluorspar reduces the melting point to about $1000^{0} C$ .

The electrolytic cell is a large steel tank having a lining of carbon (graphite) on the inner side. The carbon (graphite) lining acts as a cathode. A set of carbon (graphite) rods dipped in the molten electrolyte acts as an anode. On passing electric current, electrolysis of alumina takes place. Aluminium is formed at the cathode and oxygen gas is liberated at the anode.

The electrode reactions are as follows:Cathode: ${Al}^{3 +} + 3 e^{-} \overset{}{\to} {Al}_{(l)}$ (Reduction)

Anode: $2 {O_{2}}^{-} \overset{}{\to} O_{2} + 4 e^{-}$ (Oxidation)

The molten aluminium is heavier than the electrolyte used and hence, it sinks to the bottom of the tank from where it is removed periodically.

The oxygen gas liberated at the anode reacts with the carbon anode and forms carbon dioxide gas.

$C_{(s)} + O_{2 (g)} \overset{}{\to} {CO}_{2 (g)}$

As anode gets oxidised during the electrolysis of alumina, it has to be replaced from time to time.

Explain the electrochemical reduction method to obtain aluminium from alumina with diagram.

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