The shape of the lesson
By the end of the lesson, learners can
- Clean air and its pollutants: Learn each pollutant as a pair: where it comes from, and what harm it does.
- Oxides of nitrogen and catalytic converters: Run the engine in the simulator and raise the temperature.
- Acid rain and how to reduce it: Dissolve sulfur dioxide and nitrogen dioxide in rain water in the simulator and watch the pH fall.
- Air: 78% N2, 21% O2, rest noble gases (mainly argon) and CO2.
- CO and particulates: incomplete combustion; toxic, lung damage.
- SO2 and NOx: acid rain; fix with low-sulfur fuel, FGD, catalytic converters.
- Extended: 2NO + 2CO → N2 + 2CO2.
One picture every idea returns to
Clean, dry air is about 78% nitrogen, 21% oxygen and the remaining 1% is a mixture of noble gases (mainly argon) and carbon dioxide. Pollutants each have a source and an effect: carbon monoxide (incomplete combustion) is toxic; particulates (incomplete combustion) cause respiratory problems and cancer; oxides of nitrogen (car engines) cause acid rain, photochemical smog and respiratory problems; sulfur dioxide (burning fuels containing sulfur) causes acid rain; carbon dioxide and methane cause global warming. Acid rain is reduced by catalytic converters in vehicles, low-sulfur fuels and flue gas desulfurisation with calcium oxide. Extended: oxides of nitrogen form when nitrogen and oxygen from the air react at the high temperature inside an engine, and a catalytic converter removes them: 2NO + 2CO → N2 + 2CO2.
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, What we add to the air.. Clean air is almost all nitrogen and oxygen. Put the figure on the board: it is the one picture every idea in the lesson returns to. | Whole class, then pairs |
| 5 to 13 min | Teach and check: Clean air and its pollutants | Learn each pollutant as a pair: where it comes from, and what harm it does. | Whole class, then pairs |
| 13 to 21 min | Teach and check: Oxides of nitrogen and catalytic converters | Run the engine in the simulator and raise the temperature. Project tab 3 of the lab (Nitrogen and sulfur lab, nitrogen oxides) and let a student drive it while the class predicts. | Pairs |
| 21 to 30 min | Teach and check: Acid rain and how to reduce it | Dissolve sulfur dioxide and nitrogen dioxide in rain water in the simulator and watch the pH fall. Project tab 4 of the lab (Nitrogen and sulfur lab, acid rain) and let a student drive it while the class predicts. | Quiz-Quiz-Trade |
| 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, 17 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 Acid rain and how to reduce it, 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.
Quiz-Quiz-Trade
Each student holds a card with a question on the front and the answer on the back. They pair up, quiz each other, coach if needed, trade cards and find a new partner. Three rounds covers the whole set.
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 |
|---|---|
| A catalytic converter does not remove carbon dioxide: it makes more of it, from carbon monoxide. | Carbon dioxide causes global warming, not acid rain; acid rain comes from sulfur dioxide and oxides of nitrogen. And the nitrogen in NO x comes from the air, not from the fuel. |
Air pollution: worksheet
6 questions, 17 marks. Written in the style of the papers; no past paper question is reproduced.
State the composition of clean, dry air.
For each pollutant, give one source and one adverse effect: (a) carbon monoxide, (b) sulfur dioxide.
Give two adverse effects of oxides of nitrogen in the air.
(Extended) Explain how nitrogen monoxide forms in a car engine and write an equation for its removal in a catalytic converter.
Describe two ways of reducing the emission of sulfur dioxide from power stations and explain how one of them works.
A student says catalytic converters help to stop global warming. Evaluate this statement.
Answer key and marking notes
- About 78% nitrogen.
- About 21% oxygen.
- The rest (about 1%) is a mixture of noble gases, mainly argon, and carbon dioxide.
- (a) Source: incomplete combustion of carbon-containing fuels.
- (a) Effect: toxic (stops the blood carrying oxygen).
- (b) Source: combustion of fossil fuels containing sulfur compounds.
- (b) Effect: acid rain.
- Acid rain.
- Photochemical smog (or respiratory problems).
- Nitrogen and oxygen from the air react at the high temperature in the engine.
- N2 + O2 → 2NO
- In the converter: 2NO + 2CO → N2 + 2CO2
- Use low-sulfur fuels (remove sulfur from the fuel before burning).
- Flue gas desulfurisation.
- Calcium oxide, a base, reacts with the acidic sulfur dioxide in the waste gases: CaO + SO2 → CaSO3.
- Catalytic converters remove carbon monoxide and oxides of nitrogen, reducing toxic gases and acid rain.
- But they convert CO into CO2, a greenhouse gas, so they do not reduce global warming; the statement is wrong.
8 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.
Which row gives the approximate composition of clean, dry air?
| nitrogen | oxygen | other gases | |
|---|---|---|---|
| A | 78% | 21% | 1% |
| B | 21% | 78% | 1% |
| C | 78% | 1% | 21% |
| D | 50% | 49% | 1% |
- AA
- BB
- CC
- DD
Which pollutant is formed by the incomplete combustion of carbon-containing fuels and is toxic?
- Acarbon monoxide
- Bcarbon dioxide
- Csulfur dioxide
- Dmethane
Which pair of pollutants are the main causes of acid rain?
- Asulfur dioxide and oxides of nitrogen
- Bcarbon dioxide and methane
- Ccarbon monoxide and particulates
- Dmethane and sulfur dioxide
What is the source of most of the sulfur dioxide in the air?
- Acombustion of fossil fuels that contain sulfur compounds
- Bcar engines reacting nitrogen with oxygen
- Cincomplete combustion of petrol
- Ddigestion in cattle
A power station burns coal. Which method reduces the amount of sulfur dioxide released from its chimneys?
- Aflue gas desulfurisation using calcium oxide
- Bfitting a catalytic converter
- Cplanting trees around the power station
- Dburning the coal in a smaller supply of air
Nitrogen monoxide and carbon monoxide pass through the catalytic converter shown. Two gases, X and Y, leave it. What are X and Y?
- Anitrogen and carbon dioxide
- Bnitrogen dioxide and carbon dioxide
- Coxygen and carbon
- Dammonia and water
Why do car engines produce oxides of nitrogen even though petrol does not contain nitrogen compounds?
- Anitrogen and oxygen from the air react at the high temperature inside the engine
- Bthe catalytic converter turns carbon dioxide into oxides of nitrogen
- Cpetrol is a mixture of hydrocarbons and nitrogen compounds
- Dnitrogen is formed when carbon monoxide decomposes
Which equation shows a reaction that removes carbon monoxide in a catalytic converter?
- A2CO + O2 → 2CO2
- B2CO2 → 2CO + O2
- CCO + H2O → CH2O2
- D2CO → 2C + O2
Quiz key
Clean, dry air is about 78% nitrogen, 21% oxygen and 1% other gases, mainly argon and other noble gases with a little carbon dioxide. Row B swaps nitrogen and oxygen. Row C puts oxygen at only 1%, far too low to support life. Row D does not match the real composition.
With a limited supply of oxygen, carbon in a fuel forms carbon monoxide, CO, which is toxic because it stops the blood carrying oxygen. Carbon dioxide forms in complete combustion and causes global warming rather than poisoning. Sulfur dioxide comes from sulfur compounds in fuels. Methane comes from decomposing vegetation and livestock, not from combustion.
Sulfur dioxide and oxides of nitrogen dissolve in rain water to form acids, causing acid rain. Carbon dioxide and methane are the greenhouse gases linked to global warming. Carbon monoxide is toxic and particulates cause respiratory problems, but neither causes acid rain. Methane is not an acidic oxide, so the last pair is only half right.
Fossil fuels such as coal contain sulfur compounds, which burn to form sulfur dioxide. Car engines produce oxides of nitrogen from nitrogen and oxygen in the air, not sulfur dioxide. Incomplete combustion produces carbon monoxide and particulates. Digestion in cattle releases methane.
In flue gas desulfurisation, calcium oxide (a base) reacts with the acidic sulfur dioxide in the waste gases: CaO + SO2 → CaSO3. Catalytic converters are fitted to vehicles to remove carbon monoxide and oxides of nitrogen. Trees remove carbon dioxide, not sulfur dioxide. Less air would cause incomplete combustion and produce carbon monoxide, while the sulfur would still be released.
In the converter 2NO + 2CO → N2 + 2CO2: nitrogen monoxide is reduced to nitrogen and carbon monoxide is oxidised to carbon dioxide. Nitrogen dioxide is itself a pollutant that causes acid rain, so making it would defeat the purpose. Oxygen and solid carbon are not formed. There is no hydrogen in NO or CO, so ammonia and water cannot form.
Air drawn into the engine is about 78% nitrogen. At the very high temperature of the burning fuel, nitrogen reacts with oxygen: N2 + O2 → 2NO. The catalytic converter removes oxides of nitrogen; it does not make them. Petrol is a mixture of hydrocarbons only. Carbon monoxide contains no nitrogen, so it cannot form nitrogen.
In the converter carbon monoxide is oxidised to carbon dioxide: 2CO + O2 → 2CO2 (or, with nitrogen monoxide, 2NO + 2CO → N2 + 2CO2). The second equation is the reverse, which would make more carbon monoxide. Carbon monoxide does not react with water to form CH2O2 in a converter. Decomposing CO into carbon and oxygen does not happen and would leave soot in the exhaust.
What to project
The student lesson embeds these tabs. Open them full screen on the projector; every slider has a drag handle on the stage.
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.