Chemistry
The following is a sketch of an electrolytic cell used in the extraction of aluminium :
(i) What is the substance of which the electrodes A and B are made?
(ii) At which electrode (A or B) is the aluminium formed ?
(iii) What are the two aluminium compounds in the electrolyte C ?
(iv) Why is it necessary for electrode B to be continuously replaced ?
Answer
(i) Electrodes A and B are made of graphite (carbon).
(ii) Aluminium is formed at cathode (i.e., electrode A).
(iii) Fused alumina (Al2O3) and Cryolite (Na3AlF6) are the compounds in the electrolyte C.
(iv) The graphite [carbon] anodes (i.e electrode B) are continuously replaced during the electrolysis because :
- The oxygen evolved at the anode escapes as a gas or reacts with the carbon anode.
- The carbon anode is thus oxidized to carbon monoxide which either burns giving carbon dioxide or escapes out through an outlet. 2C + O2 ⟶ 2CO [2CO + O2 ⟶ 2CO2]
- The carbon anode is hence consumed and renewed periodically after a certain period of usage.
Related Questions
Brass is an alloy of :
- Copper and tin
- Copper and zinc
- Zinc and lead
- Lead and tin
Correct the following statement — Haematite is the chief ore of aluminium.
The metal oxide which can react with acid as well as alkali is :
- Silver oxide
- Copper [II] oxide
- Aluminium oxide
- Calcium oxide
In the extraction of aluminium :
(i) Which soln. is used to react with bauxite as a first step in obtaining pure aluminium oxide.
(ii) The aluminium oxide for the electrolytic extraction of aluminium is obtained by heating aluminium hydroxide. Write the equation for this reaction.
(iii) Name the element which serves as the anode and cathode in the extraction of aluminium.
(iv) Write equation for the reaction at the cathode during the extraction of aluminium by electrolysis.
(v) Give the equation for the reaction at the anode when aluminium is purified by electrolysis.