Question

A layer of coke is spread over bauxite during extraction of aluminium. This acts as an $\_\_\_\_\_.$
(a) Flux
(b) Slag to remove impurities
(c) Reducing agent
(d) Insulation and does not allow heat to escape

Answer 1

Hint:Bauxite is one of the most common ore of the aluminium found in the nature. It is used as extraction of the aluminium by different steps of purifications like purifying the bauxite, electrolysis of the residue etc. to get the best aluminium.

Complete step-by-step answer:First we discuss how bauxite is related to aluminium:
Bauxite is the ore of Aluminium, which is processed to produce Alumina. The formula of bauxite is $A{l_2}{O_3}.2{H_2}O$
Now, we start with the discussing how aluminium is extracted and refined:
(i) The first step to extract the aluminium is to purify the bauxite:The purification is done by the Bayer’s Process,The bauxite ore is powdered and then is reacted with sodium hydroxide.
$A{l_2}{O_3}.2{H_2}O + 2NaOH + {H_2}O \to 2Na\left[ {Al{{\left( {OH} \right)}_4}} \right]$
In these process, alumina is dissolved into sodium hydroxide and forms sodium aluminate,
$A{l_2}{O_3} + 2O{H^ - } + 3{H_2}O \to 2{\left[ {Al{{\left( {OH} \right)}_4}} \right]^ - }$
The ferric oxides and silica present in the ores removed by filtration due to their insoluble property. The residue is heated to form pure alumina.
(ii) The next step is electrolysis of the alumina:The alumina is dissolved in the molten cryolite and is electrolysed. The electrolysis is carried into a tank which is lined with carbon and the reaction takes place as follows:
At cathode:
$A{l^{3 + }} + 3{e^ - } \to Al$
At anode:
$C + {O^{2 - }} \to CO + 2{e^ - }$
The electrolyte is covered with a layer of powdered coke for insulation and heat resistant.
(iii) Refining of aluminium:Refining is done by electrolysis of ore in an iron tank which is lined with carbon.
From the above discussion we get that the coke is spread over bauxite during extraction of aluminium for insulation and heat resistant purposes.

Hence, the correct option is (d) Insulation and does not allow heat to escape.

Note: In the extraction of aluminium, cryolite is used to decrease the melting point of the alumina and increase the electrical conductivity of the alumina and the refining is done by Hoop’s electrolytic method.