Common atmospheric pollutants (AQA GCSE Chemistry: Combined Science)

Older automobiles that are still in use are tested every year to monitor the levels of pollution in their exhaust fumes.

The maximum allowed percentages of exhaust pollutants for petrol cars are shown in the table.

Explain how burning petrol in a car produces carbon monoxide.

Suggest three reasons why the maximum allowed percentage of carbon monoxide for newer cars is much less than for older cars.

Give two reasons for there being a maximum allowed percentage of unburned hydrocarbons present in exhaust fumes.

Exhaust fumes contain oxides of nitrogen which are also pollutants.

Describe how oxides of nitrogen are produced in car engines.

Advances in technology led to the production of catalytic converters. 

These are fitted to car exhausts to reduce the amount of pollutants they release.

Nitrogen dioxide is a pollutant that reacts to produce nitrogen and oxygen in catalytic converters.

Complete and balance the equation for the reaction.

____ NO₂ ⟶ ________ + ____ O₂ 

Give two effects of atmospheric pollution which are reduced by using catalytic converters.

The catalyst in catalytic converters is a mixture of three elements.

Where in the periodic table are these elements most likely to be found?

Tick one box. 

Catalytic converters are usually made up of three elements and are fitted into car exhausts to reduce the effect of pollutants.

Which group of elements would most likely be used?

Limestone is eroded by acid rain.

Which substance falls as acid rain?

County planners are attempting to protect the environment around a reservoir that is surrounded by trees.

It is a large reservoir with only one access road and a car park that is positioned a few kilometres from the reservoir. 

A steam train has been installed to ferry visitors from the car park to the reservoir, accomodation or activities.

A map of the area is shown in Figure 1.

Figure 1

The steam train uses coal for the furnace which causes environmental problems.

Explain why.

The planners have stated that the overall amount of carbon dioxide added to the atmosphere must be kept the same to account for the train. 

The steam train would be considered as ‘carbon neutral’ if wood were used instead of coal.

Suggest why.

This question is about biodiesel.

Biodiesel can be made from many types of vegetable oils. 

A group of scientists compared the exhaust emissions when fossil diesel (diesel produced from crude oil) or biodiesel were used as fuels.

Some of the relative amounts of these exhaust emissions are shown in the bar chart in Figure 1.

Figure 1

Explain the environmental benefits of using biodiesel over diesel, using the information in Figure 1.

Biodiesel is also known as a green fuel because the life-cycle emission of carbon dioxide from biodiesel is less than that from fossil diesel. 

Use the information above to explain why the contribution of biodiesel to global warming is considered to be much less than that of fossil diesel.

This question is about the effects of sulfur dioxide in the atmosphere.

Fossil fuels contain impurities of sulfur. 

When combustion occurs, sulfur dioxide is produced. 

Measures are taken to prevent sulfur dioxide from being released into the atmosphere.

Explain why it is important that sulfur dioxide is not released into the atmosphere.

Three of the methods used to remove sulfur dioxide from gases produced when fossil fuels are burned are, dry gas desulfurisation (D), wet gas desulfurisation (W) and seawater gas desulfurisation (S)

Information about the three methods is given in Figure 1 and Table 1 below.

Figure 1

Table 1

Evaluate the three methods of removing sulfur dioxide from the waste gases during the combustion of fossil fuels.

Compare the three methods, using the data provided to justify your conclusion.

Incomplete combustion occurs when there is insufficient oxygen for a reaction.

Which are the two main substances formed during incomplete combustion, aside from water?

Cars running on fossil fuels contribute a high amount of pollutants into the atmosphere, one of which is carbon dioxide. 

Which other gas is produced by the internal combustion engine in a car?

This question is about sulfur. 

Describe the structure of an atom of sulfur. 

Use your periodic table to help you. 

Limestone is eroded as a result of burning fossil fuels containing sulfur. 

Explain how this happens.

Explain why sulfur dioxide has a low melting point. 

You should refer to its structure and bonding in your answer. 

Name one other pollutant gas that results in the erosion of limestone. 

Natural gas is a fossil fuel consisting mainly of methane.

When methane burns it can produce carbon monoxide as well as carbon dioxide. 

Explain why carbon monoxide is produced when methane is burned. 

Write a balanced symbol equation for the combustion of methane, CH₄, to produce carbon monoxide, CO and one other product.

Give one hazard associated with carbon monoxide.

Wood is more sustainable than natural gas and other fossil fuels. 

Suggest two reasons why. 

Complete the energy level diagram for the combustion of methane.

On the completed diagram, label:

• activation energy
• overall energy change

This question is about pollutants.

Fossil fuels, such as coal, are burned to release energy. 

Hydrogen, sulfur, and carbon are all elements found in coal.

Name two products released when coal burns that have a negative effect on the environment.

State the impact each of the products you have named have. 

Oxides of nitrogen also impact the environment.

Explain how oxides of nitrogen are formed in car exhausts. 

Describe two effects of oxides of nitrogen being released into the atmosphere. 

Fossil fuels produce sulfur dioxide when they burn due to containing sulfur impurities.

Sulfur dioxide has many environmental effects such as acid rain so its release should be avoided. 

To overcome this issue, three methods are used to ensure it is removed from the other gases formed during combustion:

• Dry gas desulfurisation (DG)
• Wet gas desulfurisation (WG) 
• Seawater gas desulfurisation (SG)

Information about the three methods is given in the bar chart in Figure 1 and Table 1.

Figure 1

Table 1 

Evaluate the three methods of removing sulfur from waste gases. 

Sulfur dioxide will dissolve in water. 

Explain what colour universal indicator will turn when it is added to the solution.

All acids contain the same ion. 

What is the formula of this ion? 

Hydrochloric acid is a strong acid. 

Explain why a strong acid has a low pH.

This question is about pollution. 

Electricity can be generated through burning fossil fuels, such as coal, in power stations. 

Doing this releases harmful pollutant gases such as sulfur dioxide (which causes acid rain) and carbon dioxide. 

Limestone can be used to prevent sulfur dioxide entering the atmosphere, however it also releases 'locked up' carbon dioxide. 

How does limestone remove sulfur dioxide?

How is carbon dioxide released from the limestone in Figure 1?

Two products are produced as a result of incomplete combustion of the fuel.

Name these two products and give a reason for each one why it should not be released into the environment. 

Why does the release of carbon dioxide cause an environmental problem?