The blast furnace and aluminium Cambridge IGCSE Chemistry (9–1) revision
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In plain words
Iron is made in a blast furnace: a tower as tall as a block of flats, fed with iron ore, coke and limestone at the top and blasted with hot air at the bottom. Aluminium is made by passing a huge electric current through its molten ore.
Three things to know
- Blast furnace: coke burns to give heat and carbon dioxide (C + O₂ → CO₂), which reacts with more coke to make carbon monoxide (CO₂ + C → 2CO). Carbon monoxide reduces the ore, hematite: Fe₂O₃ + 3CO → 2Fe + 3CO₂.
- Limestone removes sandy impurities. It decomposes (CaCO₃ → CaO + CO₂) and the calcium oxide reacts with silicon dioxide to form slag (CaO + SiO₂ → CaSiO₃).
- Aluminium: its ore, bauxite, is purified to aluminium oxide, which is dissolved in molten cryolite and electrolysed. Aluminium forms at the cathode and oxygen at the carbon anodes, which burn away and have to be replaced.
Tips and tricks
- The reducing agent in the blast furnace is carbon monoxide, not carbon. This is asked a lot.
- Cryolite lowers the temperature needed, which saves energy.
It lands in your notebook with its questions as flashcards.
The blast furnace and aluminium: 6 questions and answers
These are the quiz’s questions. Do the quiz first, then come back here for the ones that got you.
What is the main ore of iron?
Hematite is mostly iron(III) oxide.
What reduces the iron(III) oxide in a blast furnace?
Fe₂O₃ + 3CO → 2Fe + 3CO₂.
What is limestone added to the blast furnace for?
It forms calcium oxide, which reacts with silicon dioxide.
What is the main ore of aluminium?
It is purified to give aluminium oxide.
Why are the anodes in the aluminium cell replaced often?
Hot carbon and oxygen make carbon dioxide.
At which electrode does aluminium form?
Aluminium ions are positive, so they go to the negative electrode.
Quiz
6 questions
Tap an answer and you’ll see straight away whether it’s right, and why.
Worksheet
4 questions, 9 marks. Write your answers on paper, then check them.
The blast furnace and aluminium
Cambridge IGCSE Chemistry (9–1) 0971 · 9 marks · papermunch.org
Name ______________________________ Date ______________
Name the three raw materials put into the top of a blast furnace, and state the job of the coke.[3]
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Iron ore (hematite), coke and limestone. Coke burns to give heat and forms carbon monoxide, which reduces the iron ore.
Write the equation for the reduction of iron(III) oxide by carbon monoxide.[2]
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Fe₂O₃ + 3CO → 2Fe + 3CO₂.
Explain why aluminium oxide is dissolved in molten cryolite before it is electrolysed.[2]
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It lowers the temperature needed (aluminium oxide has a very high melting point), which saves energy and money.
Explain why the carbon anodes in the aluminium cell have to be replaced regularly.[2]
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Oxygen is formed at the anodes and reacts with the hot carbon to make carbon dioxide, so the anodes burn away.
Answers: The blast furnace and aluminium
- 1. Iron ore (hematite), coke and limestone. Coke burns to give heat and forms carbon monoxide, which reduces the iron ore.
- 2. Fe₂O₃ + 3CO → 2Fe + 3CO₂.
- 3. It lowers the temperature needed (aluminium oxide has a very high melting point), which saves energy and money.
- 4. Oxygen is formed at the anodes and reacts with the hot carbon to make carbon dioxide, so the anodes burn away.