Question

The following reactions take place in the blast furnace in the preparation of impure iron. Identify the reaction pertaining to the formation of slag.
A.  $2C(s) + O_2 \to 2CO2(g)$ 
B. ${{CaCO_3(s) }} \to {{CaO(s) + CO_2(g)}}$
C. \[{{CaO(s) + SiO_2(s) }} \to {{CaSiO_3(s)}}\]

Answer 1

Hint: Here, we need to recall the process of smelting i.e. reduction of iron (III) oxide to iron which occurs in blast furnaces and the reactions taking place therein.

Complete step by step answer:
Iron is extracted from the iron ore in a huge container called a blast furnace. Iron ores like hematite contain iron(III) oxide, ${Fe_2}O_3$. The oxygen is removed from iron(III) oxide which leaves behind an iron. Reactions in which the oxygen is removed are called reduction reactions.
Carbon is more reactive than the iron, so it displaces iron from the iron(III) oxide. In this reaction, the iron(III) oxide is reduced to iron, and the carbon is oxidized to carbon dioxide. In blast furnace, it is very hot that the carbon monoxide can be used, in place of the carbon, to reduce iron(III) oxide.
Raw materials for the reaction are:

Raw material	Contains	Function
Iron ore (haematite)	Iron(III) oxide	A compound which contains an iron
Coke	Carbon	It burns in the air that produces heat, and further reacts to form a carbon monoxide (needed to reduce the iron oxide)
Limestone	Calcium carbonate	Helps to remove an acidic impurity from iron by reacting with them to form a molten slag
Air	Oxygen	Allows coke to burn, and produces heat

The calcium carbonate in limestone decomposes thermally to form a calcium oxide.
\[CaC{O_3}\left( s \right){\text{ }} \to {\text{ }}CaO\left( s \right){\text{ }} + {\text{ }}C{O_2}\left( g \right)\].
The calcium oxide reacts with silica (sand) impurities in hematite, to produce a slag - which is a calcium silicate.
\[CaO\left( s \right){\text{ }} + {\text{ }}Si{O_2}\left( s \right){\text{ }} \to {\text{ }}CaSi{O_3}\left( l \right)\].

> Slag is fused and during reduction of metal, separation of vitrified matter takes place from its ore. The reaction is a neutralization reaction. Calcium oxide is a basic oxide (as it is a metal oxide) and silica is an acidic (as it is a non-metal oxide).

Thus, option C is correct.

Note: Remember that smelting process takes place where extractive metallurgy is used to extract metals from ores and it uses heat to decompose an ore. The slag that is produced is also called a cinder.