In the electrolysis of molten aluminium oxide for extraction of aluminium, the following reactions take place:
1. \mathrm{Al^{3+} + 3e^- \rightarrow Al}
2. 2\mathrm{O^{2-}} \rightarrow \mathrm{O_2} + 4\mathrm{e^-}
3. \mathrm{C + O_2 \rightarrow CO_2}
4. \mathrm{Al_2O_3 \rightleftharpoons 2Al^{3+} + 3O^{2-}}
The reaction that takes place at the negative electrode is:
(a) 1
(b) 2
(c) 3
(d) 4
(a) 1
Explanation –
The negative electrode is the cathode where reduction takes place. At the cathode, the positively charged Al3+ ions get attracted, gain 3 electrons, and get deposited as aluminium metal.
\mathrm{Al^{3+} + 3e^- \rightarrow Al}Reaction (2) takes place at the anode (oxidation), reaction (3) is the reaction of carbon anode with oxygen, and reaction (4) is the dissociation of alumina.
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