WAEC Chemistry 2024 Paper

Concept:In the blast furnace, limestone acts as a flux to remove impurities from the iron ore.Explanation:Iron ore contains impurities such as sand, mainly silicon dioxide, $\mathrm{SiO}_2$.Limestone is mainly calcium carbonate, $\mathrm{CaCO}_3$.At the high temperature inside the blast furnace, limestone decomposes as:$$\mathrm{CaCO}_3 \xrightarrow{\Delta} \mathrm{CaO} + \mathrm{CO}_2$$The calcium oxide, $\mathrm{CaO}$, formed then reacts with the acidic impurity $\mathrm{SiO}_2$:$$\mathrm{CaO} + \mathrm{SiO}_2 \rightarrow \mathrm{CaSiO}_3$$The product, calcium silicate, $\mathrm{CaSiO}_3$, forms the molten slag.This slag is lighter than molten iron and is removed easily.Therefore, the main function of limestone is to remove impurities, not to act as a catalyst or reducing agent.Answer:B. remove impurities