What pollutants are produced when fuels burn, and what problems do they cause?
Pollution from fuels: incomplete combustion and carbon monoxide and soot, sulfur dioxide and oxides of nitrogen, acid rain, and the advantages and disadvantages of hydrogen as a fuel.
A focused answer to Edexcel GCSE Chemistry topic 8, covering incomplete combustion and the production of carbon monoxide and soot, the formation of sulfur dioxide and oxides of nitrogen, the problems these pollutants cause including acid rain, and the advantages and disadvantages of using hydrogen as a fuel.
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What this dot point is asking
Edexcel wants you to explain incomplete combustion and the production of carbon monoxide and soot, describe how sulfur dioxide and oxides of nitrogen form, explain the problems these pollutants cause including acid rain, and discuss the advantages and disadvantages of hydrogen as a fuel. The origins of each pollutant and acid rain are the key marks.
Incomplete combustion
If a fuel burns in a limited supply of oxygen, it undergoes incomplete combustion:
The problems these cause:
- Carbon monoxide is a toxic gas that is colourless and odourless, so it is hard to detect. It binds to haemoglobin in the blood in place of oxygen, reducing the oxygen carried around the body, which can cause unconsciousness and death.
- Soot (carbon particulates) causes breathing problems, dirties buildings, and can contribute to global dimming.
Sulfur dioxide and oxides of nitrogen
Two more pollutants come from impurities and from the air:
- Sulfur dioxide () forms when sulfur impurities in the fuel burn in oxygen: .
- Oxides of nitrogen (such as and ) form when nitrogen and oxygen from the air react at the high temperatures inside an engine.
Acid rain
Acid rain causes serious damage:
- It erodes buildings and statues made of limestone and marble (which react with acid).
- It harms trees and damages forests.
- It makes lakes and rivers too acidic for fish and other aquatic life.
These pollutants can be reduced by removing sulfur from fuels before they are burned and by fitting catalytic converters to vehicles.
Hydrogen as a fuel
Hydrogen can be burned as a fuel: .
- Advantages: the only product is water, so it produces no carbon dioxide, carbon monoxide, soot or sulfur dioxide, making it very clean.
- Disadvantages: hydrogen is a gas that is difficult to store and transport (it must be compressed or liquefied), it is explosive and so harder to handle safely, and making the hydrogen often uses energy from fossil fuels.
Try this
Q1. Name the two carbon-containing products of incomplete combustion. [2 marks]
- Cue. Carbon monoxide and carbon (soot).
Q2. Explain how sulfur dioxide is formed when a fuel burns. [1 mark]
- Cue. Sulfur impurities in the fuel burn in oxygen to form sulfur dioxide.
Q3. Give one advantage and one disadvantage of using hydrogen as a fuel. [2 marks]
- Cue. Advantage: the only product is water (no carbon dioxide). Disadvantage: it is hard to store and transport (and is explosive).
Exam-style practice questions
Practice questions written in the style of Pearson Edexcel exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Edexcel 20184 marksWhen a fuel burns in a limited supply of air, incomplete combustion can occur. Name the two carbon-containing products of incomplete combustion, and explain why carbon monoxide is dangerous.Show worked answer →
A 4-mark incomplete-combustion question.
Incomplete combustion produces carbon monoxide and carbon (soot) (1 mark for each product). Carbon monoxide is dangerous because it is a toxic gas that is colourless and odourless, so it cannot be detected easily (1 mark), and it binds to haemoglobin in the blood in place of oxygen, reducing the amount of oxygen the blood can carry, which can be fatal (1 mark).
Markers reward naming both carbon monoxide and soot, and explaining the reduced oxygen transport in the blood.
Edexcel 20214 marksBurning some fuels releases sulfur dioxide and oxides of nitrogen. Explain how each of these gases is formed during combustion, and describe one environmental problem they cause.Show worked answer →
A 4-mark pollutant-formation question.
Sulfur dioxide is formed when sulfur impurities in the fuel burn in oxygen (1 mark). Oxides of nitrogen are formed when nitrogen and oxygen from the air react together at the high temperatures inside an engine (1 mark). Both gases dissolve in water in the atmosphere to form acids, producing acid rain (1 mark), which damages buildings and statues, harms trees and makes lakes and rivers too acidic for aquatic life (1 mark).
Markers reward the different origins (sulfur from the fuel; nitrogen oxides from the air in the engine) and acid rain with a specific effect.
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Sources & how we know this
- Pearson Edexcel GCSE (9-1) Chemistry (1CH0) specification — Pearson Edexcel (2016)