The shape of the lesson
By the end of the lesson, learners can
- The reactions, bottom to top: Follow the gases up the furnace.
- From pig iron to steel: The iron from the furnace, pig iron, contains about 4% carbon, which makes it brittle.
- Raw materials: hematite, coke, limestone, hot air.
- Heat: C + O2 → CO2. CO: CO2 + C → 2CO.
- Reduction: Fe2O3 + 3CO → 2Fe + 3CO2.
- Slag: CaO + SiO2 → CaSiO3.
One picture every idea returns to
The raw materials are hematite (iron ore, Fe2O3), coke (carbon), limestone (CaCO3) and hot air. Coke burns: C + O2 → CO2, giving heat. Carbon dioxide reacts with more coke: CO2 + C → 2CO. Carbon monoxide reduces the ore: Fe2O3 + 3CO → 2Fe + 3CO2. Limestone decomposes, CaCO3 → CaO + CO2, and the calcium oxide removes sand: CaO + SiO2 → CaSiO3 (slag).
Forty-five minutes, phase by phase
| Time | Phase | What happens in the room | Grouping |
|---|---|---|---|
| 0 to 5 min | Hook: predict | Open with the question in the title, Coke, ore, limestone and air.. A blast furnace runs day and night, turning a rock called hematite into molten iron. Put the figure on the board: it is the one picture every idea in the lesson returns to. | Whole class, then pairs |
| 5 to 17 min | Teach and check: The reactions, bottom to top | Follow the gases up the furnace. | Whole class, then pairs |
| 17 to 30 min | Teach and check: From pig iron to steel | The iron from the furnace, pig iron, contains about 4% carbon, which makes it brittle. | Rally Robin |
| 30 to 36 min | Check | The four Stage 1 questions from the student lesson, answered on mini whiteboards or by show of fingers. Re-teach the one most get wrong. | Individual, then whole class |
| 36 to 43 min | Plenary | The exam-style questions from Stage 2, one at a time: thirty seconds alone, then a random call. The feedback lines in the key give the examiner's wording. | Individual, random call |
| 43 to 45 min | Exit and homework | Set the worksheet below (6 questions, 16 marks). Learners self-assess against the objectives before they leave. | Individual |
Protect the parts that carry the learning
The sequence carries about fifty minutes of material, so the lab is driven by one student while the class predicts rather than explored freely. Times are a guide.
Protected: the check at 30 minutes. It is the only individual read on whether the key idea landed, and it is not cut.
Cut first if the build overruns: the last check in From pig iron to steel, never the check or the plenary.
In a 60 minute block: run worksheet questions 1 to 3 in class as a Rally Coach set and model both the hardest worked example and its check live.
Rally Robin
Pairs take turns to say one item each, back and forth: a definition, a unit, a step of the method. Keep it fast and oral; the point is retrieval, not writing.
The full structure, with its variations and the other twelve, is on the cooperative-learning page.
What to head off, and how
| Trap learners fall into | Teaching move that pre-empts it |
|---|---|
| The main reducing agent is carbon monoxide, not carbon: it is a gas that reaches every part of the ore. | And limestone does not reduce anything; its job is to remove the sandy impurities as slag. |
Extracting iron in the blast furnace: worksheet
6 questions, 16 marks. Written in the style of the papers; no past paper question is reproduced.
Name the four raw materials added to a blast furnace.
Write equations for the three reactions that produce iron from coke and hematite in the blast furnace.
Explain the role of limestone in the blast furnace, including equations.
In the reduction of iron(III) oxide by carbon monoxide, identify the substance oxidised and the substance reduced.
Explain why the burning of coke is important in the blast furnace, apart from producing carbon dioxide.
Pig iron from the blast furnace is brittle. Explain how it is converted into steel.
Answer key and marking notes
- Hematite (iron ore).
- Coke (carbon).
- Limestone (calcium carbonate).
- Hot air.
- C + O2 → CO2
- CO2 + C → 2CO
- Fe2O3 + 3CO → 2Fe + 3CO2
- Limestone decomposes in the heat: CaCO3 → CaO + CO2.
- Calcium oxide reacts with the sand (silicon dioxide) impurity: CaO + SiO2 → CaSiO3.
- The calcium silicate forms slag, which is removed from the furnace.
- Carbon monoxide is oxidised (gains oxygen to form CO2).
- Iron(III) oxide is reduced (loses oxygen to form iron).
- The reaction is exothermic.
- It provides the high temperature needed for the other reactions and to melt the iron.
- Oxygen is blown through the molten iron to remove most of the carbon as carbon dioxide (and calcium oxide removes other impurities as slag).
- Controlled amounts of carbon and other elements are then added.
7 multiple-choice questions on this lesson
From the topic question bank. Assign them in the app for a marked score in your gradebook, or run the topic as a class game.
The diagram shows a blast furnace with four labelled points. At which point does coke react with oxygen from the hot air, producing the highest temperature in the furnace?
- AC
- BA
- CB
- DD
In the blast furnace, CaO + SiO2 → CaSiO3. What type of reaction is this?
- Aa basic oxide reacting with an acidic oxide to form a salt
- Breduction of silicon dioxide by calcium oxide
- Cthermal decomposition of calcium oxide
- Ddisplacement of silicon by calcium
Which two gases make up most of the waste gas leaving the top of a blast furnace?
- Anitrogen and carbon dioxide
- Boxygen and carbon dioxide
- Chydrogen and carbon monoxide
- Doxygen and nitrogen
Iron is produced by Fe2O3 + 3CO → 2Fe + 3CO2. The relative formula mass of Fe2O3 is 160 and Ar of Fe is 56. What is the maximum mass of iron that can be made from 320 tonnes of Fe2O3?
- A224 tonnes
- B112 tonnes
- C448 tonnes
- D160 tonnes
Coke is mainly carbon, yet carbon monoxide rather than solid coke is the main reducing agent for the iron ore. Why?
- Acarbon monoxide is a gas, so it flows through the furnace and reaches all the lumps of ore
- Bcarbon monoxide is more reactive than aluminium
- Ccoke cannot react with oxygen
- Dcarbon monoxide is made from the limestone
In the blast furnace, CO2 + C → 2CO. Which substance is oxidised in this reaction?
- Acarbon (coke)
- Bcarbon dioxide
- Ccarbon monoxide
- Dneither, because this is not a redox reaction
Iron(III) oxide contains Fe3+ ions. When it is reduced to iron in the blast furnace, what happens to each iron ion?
- Aeach Fe3+ ion gains three electrons to form an iron atom
- Beach Fe3+ ion loses three electrons to form an iron atom
- Ceach Fe2+ ion gains two electrons to form an iron atom
- Deach iron atom gains three electrons to form an Fe3+ ion
Quiz key
Hot air is blown in near the bottom, at the level of point C, so this is where coke burns: C + O2 → CO2. The reaction is strongly exothermic, making this the hottest region. Point A is the top, where the raw materials enter and the furnace is coolest. Point B is higher up, where carbon monoxide reduces the ore and limestone decomposes. Point D is the outlet where slag is tapped off; no coke burns there.
Calcium oxide is a basic (metal) oxide and silicon dioxide, the sand impurity, is an acidic (non-metal) oxide. They react together in a neutralisation-type reaction to form the salt calcium silicate, which is the slag. Silicon dioxide does not lose oxygen, so it is not reduced. Two substances combine to form one, which is the opposite of decomposition. Silicon is not released as an element, so it is not displacement.
Air is about 78% nitrogen, which is unreactive and passes straight through the furnace. The oxygen is used up burning coke, and carbon dioxide is produced by the reduction of the ore and by the decomposition of limestone. So the waste gas is mainly nitrogen and carbon dioxide (with some carbon monoxide). Little oxygen survives the hot coke, and no hydrogen is produced by the main reactions.
160 tonnes of Fe2O3 contains 2 × 56 = 112 tonnes of iron. 320 tonnes is twice as much, so it gives 2 × 112 = 224 tonnes. The value 112 tonnes is the iron in only 160 tonnes of oxide. 448 tonnes counts the iron twice over, and 160 tonnes is simply half of the oxide mass, which ignores the formula.
Solid coke touches the ore only at a few points, but carbon monoxide gas rises through the whole furnace and surrounds every lump of ore, so reduction is fast and thorough. Carbon monoxide is not more reactive than aluminium; that is why aluminium cannot be extracted this way. Coke does react with oxygen: that reaction supplies the heat. Carbon monoxide comes from carbon dioxide reacting with coke, not from limestone.
The carbon from the coke gains oxygen to form carbon monoxide, so carbon is oxidised. Carbon dioxide loses one oxygen atom to become carbon monoxide, so carbon dioxide is reduced. Carbon monoxide is the product, not a reactant that changes. Since one substance gains oxygen and another loses it, this is a redox reaction.
Fe3+ + 3e− → Fe: each ion gains three electrons and becomes a neutral atom, which is reduction. Losing electrons would make the ion even more positive. Iron(III) oxide contains Fe3+, not Fe2+. An atom that gained electrons would become negative, not Fe3+; forming Fe3+ from iron needs electrons to be lost, as happens in rusting.
Slides for this lesson
A projectable deck for every pack is on the way. Until then, present the student lesson full screen: its sections, figure and lab tabs follow the same order as the plan above.