Question

Concentrated ore of iron, coke and limestone are fed into a blast furnace from the top. 

i) Write down the reason for adding limestone along with the concentrated ore of iron. 

ii) Write down the reactions taking place at the higher temperature range in the blast furnace. 

OR 

Metals are extracted from their chief ore. 

i) Name the pencil pal ore of aluminium. 

ii) Write the equations for the reactions taking place at the anode and at the cathode during the extraction of aluminium by the electrolytic process.

Answer 1

i) Lime stone is added to blast furnace morder to remove acidic impurities (gangue) like silica (SiO₂). At high temperature, lime stone decomposed to form calcium oxide, which acts as a basic flux and removes acidic silica gaunge as calcium silicate slag.

CaCO₃  \(\overset{Heat}{\longrightarrow}\) CaO + CO₂

CaO + SiO₂ → CaSiO₃

ii) The following reaction take place at the higher temperature range (900 K – 1500 K) in the blast furnace:

C+O₂→CO₂,FeO+CO→Fe+CO₂

OR

i) The principal ore of Al is Bauxite (Al₂O₃ 2H₂O). In Hall-Heroult process for the electrolytic extration of Al, purified Al₂O₃ mixed with Na₃ALF₆ or CaF₂ acts as the electrolyte, steel cathode and graphite anode. The following reactions take place during electrolysis:

At cathode: Al₃(melt) + 3e → 4 Al(l)

At anode : The oxygen liberated at anode reacts with the carbon of anode producing CO and CO₂.

C(s) + O² (melt) → CO(g) + 2e

C(s) + 2O²(melt) → CO_2(g) + 4e^-

The overall reaction is

2Al₂O₃+3C→4Al+3CO₂