In the extraction
of aluminium
1.
Name
the process of concentration of Bauxite.
2.
Write
the cathode reaction in electrolytic reduction of alumina.
3.
Write
the function and formula of cryolite in the extraction of aluminium.
4.
Write
an equation for the action of heat on aluminium hydroxide.
5.
Draw
the diagram of extraction of aluminium.
6.
Why
is it necessary to replace anodes time to time?
7.
What
happens when aluminium ore is heated with concentrated caustic soda. Write the
balanced chemical equation for the same.
i. The process of concentration of Bauxite is done by
Bayer’s Process.
ii. The positively charged aluminium
ions (Al3+) are attracted to the cathode (negative electrode). The
aluminium ions accept electrons from the cathode and get reduced to form
aluminium atoms (or aluminium metal).
Cathode reaction:
Al3+ + 3e – → Al
iii. Alumina has a very high melting point (>20000C).
Cryolite lowers the fusion temperature from 20000C to 10000C
and enhances conductivity.
Chemical formula of cryolite: AlF3.3NaF
iv. Equation:
| ||||
|
Heat
|
|
|
|
2Al(OH)3
|
→
|
Al2O3
|
+
|
3H2O
|
|
10000C
|
|
|
|
v. Diagram
vi. As the anode gets oxidized during the electrolysis
of alumina. It has to be replaced from time to time.
vii. When
aluminium or is heated with caustic soda (NaOH) solution under high pressure for 2 to 8
hours at 1400 to 1500 C, water soluble sodium aluminate
is formed.
Al2O3 + 2NaOH → 2NaAlO2 + H2O