In the extraction of aluminium

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.


 Ans.
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


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