When limestone acts as a flux in the furnace, what are the products that float on top of the molten iron?

When limestone acts as a flux in the furnace, what are the products that float on top of the molten iron?

• A. calcium oxide and CO2
• B. calcium carbonate
• C. water
• D. calcium oxide and H2O

Answer: (B)

The key idea is that limestone acts as a flux to form slag that floats on the molten iron. When heated, limestone (CaCO3) breaks down to calcium oxide (CaO) and carbon dioxide (CO2). The CaO then reacts with impurities like silica (SiO2) to form calcium silicate and other oxides, which make up the slag. This slag is less dense than molten iron, so it rises to form a floating layer on top of the iron, while the CO2 bubbles away as gas. Among the given options, none describe the actual floating slag (mainly calcium silicate and related oxides); calcium carbonate is the starting material, not the floating product, and water isn’t involved in this flux reaction. The concept being tested is that the floating layer is slag formed from CaO reacting with impurities, not a simple product like calcium carbonate.

The key idea is that limestone acts as a flux to form slag that floats on the molten iron. When heated, limestone (CaCO3) breaks down to calcium oxide (CaO) and carbon dioxide (CO2). The CaO then reacts with impurities like silica (SiO2) to form calcium silicate and other oxides, which make up the slag. This slag is less dense than molten iron, so it rises to form a floating layer on top of the iron, while the CO2 bubbles away as gas. Among the given options, none describe the actual floating slag (mainly calcium silicate and related oxides); calcium carbonate is the starting material, not the floating product, and water isn’t involved in this flux reaction. The concept being tested is that the floating layer is slag formed from CaO reacting with impurities, not a simple product like calcium carbonate.