Question

Hoop’s process of purification of aluminium involves the formation of layers during electrolysis. It involves ______
This question has multiple correct options
A.The three layers have the same densities but different materials.
B.The three layers have different densities.
C.The upper layer is of pure aluminium which acts as a cathode.
D.The bottom layer is of impure aluminium which acts an anode and middle layer consists of cryolite and $Ba{F_2}$.

Answer 1

We have to know that Hoop’s process is a metallurgical process, used to obtain the aluminium metal of very high purity and it is an electrolytic process.

Complete step by step answer:

We can obtain aluminium of very high purity by Hoop’s process. The metal obtained in the Hall–Héroult process is 99% pure, and for several purposes it is taken as pure metal. However, we can further purify aluminium by the Hoop’s process. Let us know that Hoop’s process is an electrolytic process.
The cell that is used in this process contains an iron tank lined with carbon at the bottom.
We can use a molten alloy of copper, crude aluminium and silicon as the anode. It forms the bottom layer in the cell.
The middle layer contains molten mixture of fluorides of sodium, aluminium and barium (cryolite+${\text{Ba}}{{\text{F}}_{\text{2}}}$).
The uppermost layer contains molten aluminium. A set of graphite rods immersed in molten aluminium acts as the cathode.
During electrolysis, ${\text{A}}{{\text{l}}^{{\text{3 + }}}}$ ions from the middle layer move to the upper layer, where they get reduced to aluminum by gaining three electrons. Equal numbers of aluminium ions are produced in the lower layer. These ions move to the middle layer. We can tap pure aluminium off from time to time. We can obtain 99.99% aluminium by Hoop’s process.
From the explanation, we can say that the upper most layer contains pure molten aluminium, middle layers contains cryolite and barium fluoride and the lowest layer that is made of impure aluminium. All these layers contain substances of different densities.
Therefore, Options (B), (C) and (D) are correct.

Note:
We must know that electrolysis is one of the many methods which are widely used in industry. It is used not only for extraction of metals as well in the reduction of the impurities in metal. This process is used in the medical field as well like for permanent removal of hair, etc. Even though such an application has some side effects but for long run it is good.