Question

The complex formed with $A{l_2}{O_3}$ is leached from bauxite using concentrated $NaOH$ solution is :
A. $Na\left[ {Al{{\left( {OH} \right)}_4}} \right]$
B. $NaA{l_2}{O_4}$
C. $N{a_2}\left[ {Al{{\left( {OH} \right)}_3}} \right]$
D. $N{a_2}Al{O_2}$

Answer 1

Hint: Complex formed with $A{l_2}{O_3}$is leached from bauxite ore using concentrated $NaOH$ solution. Leaching process is used in order to get the pure alumina (aluminium oxide) from the Bauxite ore.

Complete step by step answer: Bauxite is the principle of aluminium . It is primarily made of aluminium oxide compounds (alumina) , silica , iron oxides and titanium oxides.
Bauxite is an aluminium richore and is used for the aluminium production is $A{l_2}{H_2}{O_4}$ .
Alumina is the common name of aluminium oxide $\left( {A{l_2}{O_3}} \right)$ . It is generated from Bauxite.
Now, the complex that is formed with $A{l_2}{O_3}$ is leached from Bauxite with the help of concentrated $NaOH$
Leaching is a process that is used in extractive metallurgy in which the ores are treated with chemicals to convert the valuable metals into soluble salts which the impurities remain insoluble.
What happens is, in the leaching process the bauxite ore is made to digest with a concentrated solution of $NaOH$ that produces a complex named sodium aluminate.
Reaction involved is :-
$
  A{l_2}{O_3}(s) + 2NaOH(aq) + 3{H_2}O(l)\xrightarrow[{473 - 523K}]{{35 - 36{\text{ bar}}}}2Na\left[ {Al{{\left( {OH} \right)}_4}} \right](aq) \\
  {\text{ Sodiumaluminate}} \\
 $
When this complex is made to bear $C{O_2}$ , a hydrated compound that is hydrated alumina is precipitated.
Reaction is :
$2Na\left[ {Al{{\left( {OH} \right)}_4}} \right] + C{O_2} \to A{l_2}{O_3}.x{H_2}O + 2NaHC{O_3}$
                                                        Hydrated alumina
So, option A is correct.

Note: The process used to purify the Bauxite ore to produce alumina using concentrated solution of caustic soda is called Bayer's process. The concentrated solution of caustic soda is used in order to produce soluble sodium aluminate, leaving behind the insoluble residue.