Limestone in extraction of Iron serves the purpose of

a)Reducing agent

b)Oxidising agent

c)Formation of slag

d)None of the above

Ans-[C]

Explanation- Iron ore is not pure iron oxide – it also contains an assortment of rocky material that would not melt at the temperature of the furnace, and would eventually clog it up. The limestone is added to convert this into slag which melts and runs to the bottom. The heat of the furnace decomposes the limestone to give calcium oxide

CaCO3→CaO+CO2

This is an endothermic reaction, absorbing heat from the furnace. It is therefore important not to add too much limestone because it would otherwise cool the furnace. Calcium oxide is a basic oxide and reacts with acidic oxides such as silicon dioxide present in the rock. Calcium oxide reacts with silicon dioxide to give calcium silicate.

CaO+SiO2→CaSiO3

The calcium silicate melts and runs down through the furnace to form a layer on top of the molten iron. It can be tapped off from time to time as slag. Slag is used in road making and as “slag cement” – a final ground slag which can be used in cement, often mixed with Portland cement.