Question Video: Identifying the Compound That Reduces Iron Ore inside a Working Blast Furnace Chemistry

Which of the following substances found inside a working blast furnace reduces iron ore? [A] CO [B] CO₂ [C] CaCO₃ [D] H₂O [E] O₂


Video Transcript

Which of the following substances found inside a working blast furnace reduces iron ore? (A) CO, (B) CO2, (C) CaCO3, (D) H2O, or (E) O2.

A blast furnace uses a mixture of hot air and carbon in the form of coke to reduce metal ores, like iron ores and lead ores. In the case of iron, the most commonly used iron ore is hematite, a form of iron(III) oxide. Reduction of this iron ore involves removing the oxygen, leaving the iron behind.

One way of approaching this question is to consider which of these five chemicals is capable of extracting oxygen from iron ore. For this question, I’m going to consider reduction to be the process of removing oxygen from something. We could consider electrons, but thinking about removing oxygen is more straightforward in this case.

As a quick test, we can see how these substances respond to molecular oxygen. Carbon monoxide reacts with oxygen to form carbon dioxide. So carbon monoxide is capable of acquiring more oxygen. Therefore, we can consider carbon monoxide a possibly effective reducing agent. On the other hand, carbon dioxide does not react further with oxygen. So it’s unlikely to be an effective reducing agent. And this is true of the other three chemicals. Calcium carbonate, water, and oxygen do not readily react with more oxygen. This process leaves us with the answer of carbon monoxide. But let’s look at this another way.

Let’s have a look at the role of each of these chemicals in the blast furnace. In the blast furnace, the very role of carbon monoxide is to reduce the iron ore, while the role of carbon dioxide is to react with carbon to make the carbon monoxide. So carbon dioxide is involved in the chain that produces the agent that reduces the ore. But carbon dioxide doesn’t reduce the ore itself. Calcium carbonate, usually in the form of limestone, is added to blast furnaces so that it decomposes, producing calcium oxide. Calcium oxide is there to remove silicon dioxide impurities present in the ore. In comparison to the other chemicals, you’re unlikely to find H2O in the blast furnace. However, there may be hydrocarbons in the coke, which when burned will produce H2O. However, water will not be involved in the reduction of the ore.

Let’s have a look at the last option. Oxygen is an infamous oxidant and therefore unlikely to be a reducing agent. In the blast furnace, its role is to react with carbon to make carbon dioxide. Therefore, our final answer for which substance found inside a working blast furnace reduces iron ore is carbon monoxide, CO. And here we have the balanced chemical equation for the reduction of hematite, iron(III) oxide.

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