Give the common name of an ore, from which aluminium is extracted. (b) Name the process of its extraction and describe it.

Question

(i) (a) Give the common name of an ore, from which aluminium is extracted. 

(b) Name the process of its extraction and describe it. 

(c) Name another metal, which is extracted by this process. 

(ii) (a) Give a reason, why aluminium cannot be obtained from aluminium oxide; by the “Blast Furnace Process” or “Carbon Reduction Process.” 

(b) Name the properties for which aluminium is used in: 

(I) Cooking utensils, (II) Overhead electric transmission wire. 

(c) Aluminium is more active than iron and yet there is less corrosion of the aluminium, when both are exposed to air. Explain this fact. 

(iii) (a) What is pig-iron ? 

(b) What is the main difference in chemical composition of cast iron and steel ?

Answer 1

 (i) (a) Aluminium metal is extracted from Bauxite ore [Al₂O₃ . 2H₂O]. 

(b) Aluminium metal is extracted by electrolytic reduction process, in which electric current is passed through fused aluminium oxide, the purified Bauxite. Aluminium metal is collected at cathode, while oxygen gas is liberated at anode according to the following reactions.

(c) Calcium metal is also extracted by electrolytic reduction process. 

(ii) (a) Aluminium metal is more electropositive than iron. It has the characteristic property of all the oxides of metals that highly electropositive oxides of metals cannot be reduced by heating with carbon to form free metal. Hence aluminium is not extracted by the “Blast Furnace Process”. 

(b) (I) Aluminium is a good conductor of heat, light in weight, strong and can be made passive by nitric acid. 

(II) Aluminium is a good conductor of electricity, light in weight, tough and possess high tensile strength and is resistant to corrosion. It is a cheaper metal than copper. 

(c) Aluminium metal is protected by a thin film of aluminium oxide, which sticks firmly with the metal and prevents further corrosion. 

(iii) (a) The iron, which is obtained directly from the blast furnace is known as pig iron. Besides iron, it contains about 4% of carbon and small quantities of silicon, phosphorus, manganese and sulphur. When pig iron is heated to melting and is casted into desired moulds, then it is known as cast iron. 

(b) Cast iron contains 2-5% to 4% of carbon, while steel contains 0-5% to 1-5% of carbon. Due to the higher percentage of carbon in cast iron, it resists corrosion.