Question

Purification of aluminium by electrolytic refining is carried out by :
(A) Hoope process
(B) Hall process
(C) Baeyer process
(D) Sarperck process

Answer 1

The refining of a metal by electrolysis is known as electrolytic refining. In this process impure metal is made by the anode and a thin strip of pure metal acts as cathode. On passing electric current, the impure metal gets refined.

Complete step by step answer:
I :- Hall process :- It is the process of smelting aluminum on industrial scale. Alumina or aluminium oxide is dissolved in molten cryolite .
The reaction involved in this process is :-
$2A{l_2}{O_3} + 3C \to 4Al + 3C{O_2}.$

II. Hoope process :- It was discovered by William hoopes. This process is used to get high purity aluminium metal from impure aluminium.
In this process, the bottom of the electrolytic cell is coated with carbon and made up of iron.
It have tree fused layers :-
Lower layer :- contain alloy of copper and impure aluminium
Middle layer :- Contains cryolite $\left( {N{a_3}Al{F_6}} \right)$ and barium fluoride.
Upper layer :- Contains pure aluminum that acts as cathode.
During the process of electrolysis, $A{l^{3 + }}$ ions of middle layer mode to upper layer and reduced to $Al$. These pure aluminium atoms from $99.99\%$ purity of aluminium metal.

III. Baeyer process :-
It was developed by Carl Josef Bayer. The process includes industrial refining bauxite (are of aluminum) and produce alumina (aluminium Oxide)
Bauxite contains $30 - 60\%$ alumina and rest is silica oxide, iron oxides and titanium dioxide.
In Baeyer’s process, alumina is converted into sodium aluminate.
$A{l_2}{O_2} + 2NaoH \to 2NaAl{O_2} + {H_2}O$
It also disperses silica to form silicates.
$2NaoH + Si{O_2} \to N{a_2}Si{O_3} + {H_2}O$

IV . Serperk process :-
In this process, bauxite is heated along with coke and nitrogen gas at $2000k$ temperature. The aluminum forms aluminium nitride and silica reduce to $Si$. Upon hydrolysis, aluminium nitride forms aluminum hydroxide which yields pure alumina .
$A{l_2}{O_3}.2{H_2}O + {N_2} + 3C\xrightarrow{{2000K}}2AlN + 3C{O_2} \uparrow + 2{H_2}O.$
$Si{O_2} + 2C \to Si \uparrow + 2C{O_2} \uparrow$
$AlN + 3{H_2}O \to Al{\left( {OH} \right)_3} \downarrow + N{H_3}.$

Hence, the correct option is (A) Hoope Process..

Note:
Alumina is or aluminium oxide is used to make ceramic material, abrasion resistant tiles, cutting tools etc.
Alumina is also used in cosmetics, in which it acts as a bulking agent or anticaking agent.