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General Principles And Processes of Isolation Of Elements

Long Answer Type

61.

Explain: (i) Zone refining (ii) Column chromatography.

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62.
Write down the reactions taking place in different Zones in the blast furnance during the extraction of Iron.

In the blast furnace, reduction of iron oxides takes place in different temperature ranges. Coke is burnt to get the required temperature upto about 2200K. The temperature is lower in the upper part. Hence, the reduction of iron oxides take place at lower portion.

The higher temperature range, depend on the points of corresponding intersections in the ΔrG⁰ vs T plots. (Given in ncert book)
These reactions are as follows:
At 500 – 800 K (lower temperature range in the blast furnace)–

3Fe₂O₃ + CO → 2Fe₃O₄ + CO₂
Fe₃O₄ + 4CO → 3Fe + 4 CO₂
Fe₂O₃ + CO → 2FeO + CO₂

At 900 – 1500 K (higher temperature range in the blast furnace):

C + CO₂ → 2CO
FeO + CO → Fe + CO₂

The silicate impurity of the ore is removed as slag by calcium oxide (CaO), which is formed by the decomposition of limestone (CaCO₃).
CaCO₃ → CaO +CO₂
CaO +SiO₂ → CaSiO₃flux impurtiy (slag)