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.
