AQA Chemistry 5.9.3.1–5.9.3.2
Atmospheric pollutants from fuels
Burn a fuel and you get more than carbon dioxide and water. Predict what comes out of the exhaust from what is in the fuel and how it burns, then match each pollutant to the harm it does.
Combined Science · Higher tier
Start here
Standing by a busy road.
You can smell the traffic, and an old van pulling away leaves a puff of black smoke. The fuels are mostly carbon and hydrogen.
If you had to guess, does burning them put out only carbon dioxide and water, or other substances too?
Predict the products
What is in the fuel, and how does it burn?
Carbon and hydrogen
With plenty of oxygen: carbon dioxide and water. With too little oxygen, some carbon forms carbon monoxide, or solid carbon (soot), and some fuel stays unburned.
Sulfur in the fuel
Some fuels contain sulfur as an impurity. It burns to sulfur dioxide.
S + O2SO2
High temperature
In a hot engine, nitrogen and oxygen from the air react to make oxides of nitrogen. The nitrogen comes from the air, not the fuel.
N2 + O22NO
Worked example
Diesel containing a little sulfur, burned in a hot engine with plenty of air. Carbon and hydrogen with plenty of oxygen: carbon dioxide and water. Sulfur in the fuel: sulfur dioxide. Hot engine: oxides of nitrogen. Plenty of air, so no carbon monoxide or soot expected.
Your turn · case 1 of 4
Natural gas (carbon and hydrogen only), burned in a gas cooker with plenty of air.
Tick every product you expect.
What each pollutant does
From source, to pollutant, to harm.
Carbon monoxide
Toxic. It is colourless and odourless, so it is not easily detected. This is why homes with gas boilers need a carbon monoxide detector.
Sulfur dioxide and oxides of nitrogen
Cause respiratory problems in humans, and cause acid rain. Acid rain has a lower pH than normal rain.
Particulates
Solid particles (soot) and unburned hydrocarbons. They cause global dimming, less sunlight reaching the Earth's surface, and health problems.
Think again · the boiler gas
“The poison gas from a faulty boiler is carbon dioxide.”
Your call
ChooseA gas boiler with a blocked air supply burns its fuel in too little oxygen. Which gas makes this dangerous?
Sort
Where does each pollutant come from?
Place each pollutant by its source.
Tap a card, then tap the box it belongs in. Tap a placed card to take it back.
Command words in this lesson
- Predict
- Use what is in the fuel and the conditions to say which products form.
- Describe
- Name the pollutant, where it comes from and what it does.
- Explain
- Link the cause to the effect: no smell, so not easily detected.
Key fact
Carbon monoxide is toxic and not easily detected. Sulfur dioxide and oxides of nitrogen cause respiratory problems and acid rain. Particulates cause global dimming and health problems.
Key note · AQA 5.9.3.1–5.9.3.2
Atmospheric pollutants from fuels
- Fuels are mainly carbon and hydrogen: complete combustion gives carbon dioxide and water.
- Too little oxygen: carbon monoxide, soot and unburned hydrocarbons (particulates).
- Sulfur impurities in the fuel burn to sulfur dioxide.
- At high temperatures in engines, nitrogen and oxygen from the air form oxides of nitrogen.
- Carbon monoxide: toxic, colourless, odourless, not easily detected.
- Sulfur dioxide and oxides of nitrogen: respiratory problems and acid rain. Particulates: global dimming and health problems.
Photograph this card. Tomorrow, cover it and say each line first.
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Ask MrBadmus
Mixing up which gas causes what?
The predictor uses simple rules: carbon and hydrogen give carbon dioxide and water with plenty of oxygen; too little oxygen adds carbon monoxide and particulates; sulfur gives sulfur dioxide; high temperature gives oxides of nitrogen.