Extraction of Metals - Result Question 11
11. In the Hall-Heroult process, aluminium is formed at the cathode. The cathode is made out of
(2019 Main, 12 Jan I)
(a) platinum
(b) carbon
(c) pure aluminium
(d) copper
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Answer:
Correct Answer: 11. (b)
Solution:
- In the Hall - Heroult’s process, aluminium in formed at the cathode. The cathode is made out of carbon. In this method, $Al _2 O _3$ is melted with cryolite, $Na _3\left[AlF _6\right]$ and electrolysed in a graphite lined steel tank, which serves as the cathode. The anode is also made of graphite.
The cell runs continuously and at intervals molten aluminium is drained from the bottom of the cell and more bauxite is added. The electrolytic reactions are as follows:
$ \begin{array}{lrl} \text { At cathode: } & Al^{3+}+3 e^{-} & \longrightarrow Al \\ \text { At anode: } & C(s)+O^{2-} \text { (melt) } & \longrightarrow CO(g)+2 e^{-} \\ & C(s)+2 O^{2-} \text { (melt) } & \longrightarrow CO _2(g)+4 e^{-} \end{array} $
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