Chemistry
The following questions relate to the extraction of aluminium by electrolysis :
(i) Name the other aluminium containing compound added to alumina and state it's significance.
(ii) Give the equation for the reaction that takes place at the cathode.
(iii) Explain why is it necessary to renew the anode periodically.
Answer
(i) The compound is cryolite [Na3AlF6]. It —
- lowers the fusion point of the mixture i.e., mixture fuses around 950°C instead of 2050°C.
- enhances the mobility of the fused mixture by acting as a solvent for the electrolytic mixture.
- enhances the conductivity of the mixture since, pure alumina is almost a non-conductor of electricity.
(ii) 2Al3+ + 6e- ⟶ 2Al
(iii) The anodes 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
Heating an ore in a limited supply of air or in the absence of air at a temperature just below it's melting point is known as :
- Smelting
- Ore dressing
- Calcination
- Bessemerisation
Aluminium powder is used in thermite welding because :
- it is strong reducing agent
- it is strong oxidizing agent
- it is corrosion resistant
- it is a good conductor of heat.
The metals zinc and tin are present in the alloy :
- Solder
- Brass
- Bronze
- Duralumin.
Using the information below about X and Y – complete the following questions :
X-2,8,7 Y-2,8,2 Dissolves in water and turns blue litmus red Very low solubility in water. Dissolves in HCl Tends to oxidise elements and compounds Tends to act as a reducing agent Poor electrical and thermal conductivity Good electrical and thermal conductivity No tendency to form alloys Forms alloys (i) …………… is the metallic element.
(ii) Metal atoms tend to have a maximum of …………… electrons in the outermost energy level.
(iii) Non-metallic elements tend to form …………… oxides while metals tend to form …………… oxides.
(iv) Non-metallic elements tend to be …………… conductors of heat and electricity.
(v) Metals tend to …………… electrons and act as …………… agents in their reactions with elements and compounds.