WAEC Chemistry 2010 Paper

Concept:Limestone acts as a flux in the blast furnace to remove acidic impurities from the iron ore.Explanation:Limestone, which is mainly $\mathrm{CaCO}_3$, decomposes at high temperature to form calcium oxide and carbon dioxide.$\mathrm{CaCO}_3 \rightarrow \mathrm{CaO} + \mathrm{CO}_2$The calcium oxide produced reacts with silica, $\mathrm{SiO}_2$, which is an impurity present in the iron ore.$\mathrm{CaO} + \mathrm{SiO}_2 \rightarrow \mathrm{CaSiO}_3$Calcium silicate, $\mathrm{CaSiO}_3$, is called slag.This molten slag is lighter than iron and is removed from the top of the furnace.Therefore, limestone helps to remove impurities rather than acting as a reducing agent, catalyst, or source of carbon dioxide.Answer:C. remove impurities