Question

The basic materials needed for production of iron in the blast furnace are lime stone, coke and air in addition to the iron ore. 

(i) (a) Name one iron ore and write its formula. 

(b) Hot air is blown in, at the base of the furnace; where’ it reacts with coke. Give the equation for the reaction that takes place. 

(c) Higher up in the furnace, the iron ore is reduced to iron by one of the gases produced in the furnace. Give the chemical equation for the reaction, by which this gas is produced and give a balanced equation to show, how the ore is reduced to iron. 

(ii) (a) Which compound produced from the limestone takes part in forming the slag ? Give the formula of the slag. 

(b) What is |he principal use of slag ? 

(iii) (a) Iron forms two series of slags ferrous and ferric. Using caustic soda solution, how would you distinguish between these two salts ? 

(b) How zinc is extracted from calamine ore ?

Answer 1

(i) (a) Haematite (Ferric oxide) Fe₂O₃ .

(ii) (a) The limestone decomposes at 1000°C, to form lime and carbon dioxide. Lime is the compound which takes part in the formation of slag.

Slag is calcium silicate with the formula CaSiO3 . 

(b) The slag is used in the manufacture of cement. 

(iii) (a) When caustic soda solution is added to a ferrous salt, a dirty green precipitate of ferrous hydroxide is obtained.

On the other hand, ferric salts give a reddish brown precipitate of ferric hydroxide with caustic soda. 

(b) Calamine ore is chemically zinc carbonate [ZnCO₃]. Purified ore is roasted in a reverberatory furnace, where it is decomposed to form zinc oxide and carbon dioxide gas is liberated.

ZnCO₃ ⟶ ZnO + CO₂

Zinc oxide so obtained is mixed with carbon and heated in a specially designed clay retorts, placed in a furnace, where it is reduced to zinc metal and carbon monoxide is formed, which is further used to reduce the ore. 

ZnO + C ⟶ Zn + CO 

ZnO + CO ⟶ Zn + CO₂