Question

Aluminium is extracted by:
A. Heating sodium aluminium silicate to a high temperature.
B. Treating cryolite with sodium hydroxide solution under pressure.
C. Heating aluminium oxide with coke in a furnace.
D. The electrolysis of molten aluminium oxide in fused cryolite.

Answer 1

Aluminium is extracted by the electrolysis of alumina mixed with molten cryolite. This process is known as the Hope’s process. In this process, the impure aluminium is collected over the anode and the pure aluminium is obtained on the cathode with a salt of the metal being the electrolyte.

Complete step by step answer:
In the above question, it has been asked about the extraction of aluminium being carried out by the electrolysis of which compound. The correct answer to this question is that on the electrolysis of alumina $(N{{a}_{3}}Al{{F}_{6}})$ mixed with molten cryolite $\left( A{{l}_{2}}{{O}_{3}} \right)$ during the electrolytic refining of aluminium metal, the impure metal/ore is placed at the anode of an electrolytic cell while the cathode is a thin plate of pure aluminium metal. The electrolyte consists of the solution of a salt of the aluminium metal, i.e. cryolite and calcium fluoride.
On passing the electric current, the pure aluminium metal from the anode dissolves and gets deposited at the cathode. The soluble impurities go into the solution while the remaining insoluble or the less electropositive impurities settle down below the anode as anode mud or sludge.

So, the correct answer is Option D.

Note: Not only aluminium is extracted through electrolytic refining but metals like $Cu,\text{ }Ag,\text{ }Zn,\text{ }Sn,\text{ }Pb,\text{ }Al,\text{ }Ni,\text{ }Cr,$ are also extracted from their impure ores the same way as the aluminium is extracted. The difference lies only in the electrolyte and the substances placed at the respective anode and cathode.