Question

In iron metallurgy, limestone is used :
A. To obtain heat energy
B. To reduce iron oxide into iron
C. As an iron ore
D. To remove sand ($Si{{O}_{2}}$ )

Answer 1

Hint: The molecular formula of limestone is $CaC{{O}_{3}}$ and it is also called calcium carbonate. It is used as flux in metallurgy to remove the impurities from the pure metals. Other metals used in metallurgy as a flux are lime, borax etc.

Complete Solution :
- In the question it is given that in iron metallurgy what is the role of limestone.
- Iron metallurgy means extraction of pure iron from its ore.
- In iron metallurgy lime stone plays a huge role.
- The calcium carbonate (limestone) is added to the roasted iron ore with coke.
- The chemical reaction which occurs by adding limestone is as follows.
\[CaC{{O}_{3}}\to CaO+C{{O}_{2}}\]
- In the above reaction limestone is going to convert into calcium oxide and carbon dioxide.
- The formed calcium oxide is going to react with the silica which is present as an impurity with iron.
- The chemical reaction of calcium oxide with silica is as follows.
$CaO+Si{{O}_{2}}\to CaSi{{O}_{3}}$
- Calcium oxide reacts with silica and forms calcium silicate as the product and removes the silica impurity in the purification of iron.
- Therefore In iron metallurgy, limestone is used to remove sand ($Si{{O}_{2}}$ ).
So, the correct answer is “Option D”.

Note: The chemical which is used to remove the impurities in metallurgy are called flux. The calcium silicate ($CaSi{{O}_{3}}$ ) which is formed in iron metallurgy by the reaction of limestone with silica is called slag.