Question

write the method of extraction of iron and the chemical reaction involved​

Answer 1

Answer:

(i) Haematite (Fe2O3)

(ii) Magnetite (Fe3O4

Explanation:

Extraction of iron from its oxides-

Concentrated ores of iron are mixed with lime stone and coke and fed into a Blast furnace from top. Here coke reduces oxides to the metal as follows:

FeO(s) + C(s) → Fe(sort) + CO(g) ...(i)

In two steps:

(i) FeO(s) → Fe(s) + 1/2 O2(g) [ΔG (FeO, Fe)]

(ii) C(s) + 1/2 O2(g) → CO(g) [ΔG (C, CO)] ...(ii)

From (i) and (ii), The net Gibbs energy change becomes

ΔG (C, CO) + ΔG (FeO, Fe) = Δr G ...(iii)

∴ The resultant reaction will take place when the r.h.s of equation (iii) become negative.

The reaction occurring in the blast furnance at different temperature are as follows:

At 500 - 800 K (lower temp. range)

3Fe2O3 + CO → 2Fe3O4 +CO2

Fe3O4 + 4CO → 3Fe - 4CO2

Fe2O3 + CO → 2FeO + CO2

At 900 - I500 K (higher temp. in the blast furnace)

C + CO2 → 2CO

FeO + CO2 → FeCO2

Lime stone is also decomposed to CaO which remove sillicate impurity of the ore as slag. The slag is in molten state and separates out from iron.

CaCO3(s) → CaO(s) + CO2(g)

CaO(s) + SiO2(s) → CaSiO3(fusible slag)

Iron obtained from blast furance contains 4% carbon and many impurities in smaller amount (e.g. SP, Si, Mn) is called big iron. Cast iron is different from pig iron. It has slightly lower carbon content (3%) and it is extremely hard and brittle.

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