Collins Cambridge IGCSE Chemistry (3rd ed)

This section focuses on water and air, the key ingredients of the environment. You will learn about the chemical nature of the environmental issues facing the world today. The pollution of water supplies, whether by plastics, detergents or fertilizers, are addressed.

Air quality, and the climate more generally, are also addressed, including the causes of global warming and the impact of acid rain.

There are strong links to Section 11, Organic chemistry, through the issues related to the combustion of hydrocarbon, non-renewable fuels. In addition, the nature of some of the atmospheric pollutants will link to work in Section 7, Acids, bases and salts. There will be a strong focus on the strategies that can be used to reduce the effects on the climate of global warming and atmospheric pollution.

Starting points 1. Do you know the common test used to identify the presence of water?

2. Can you name some of the main gases in clean, dry air?

3. Can you name some of the gases that cause pollution in the air?

4. Do you know about the greenhouse effect? If so, can you explain what it is?

SYLLABUS SECTIONS COVERED 10.1 Water 10.2 Fertilisers 10.3 Air quality and climate

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10

Chemistry of the environment

∆ Plastic waste in the sea.

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Chemistry of the environment INTRODUCTION

∆ Fig. 10.1 The smog over the Forbidden City in Beijing is so thick that it obscures the view from Feng Shui Hill.

Clean water and air are precious. Water from natural sources is not a pure substance.

It contains a variety of substances, some of which are beneficial and some are potentially harmful. Domestic water supplies have to be purified before they can be used safely. Fertilisers are used extensively to provide a source of nitrogen to support plant growth. However, fertilisers have to be used carefully to minimise contamination of water supplies.

Air also is not a pure substance. It provides the oxygen that all living things need to survive, and the carbon dioxide that plants need when they photosynthesise.

Nitrogen in the air is also very important for healthy plant growth, but not all plants can make use of nitrogen in this form, hence the need for fertilisers.

Unfortunately not all the air we breathe is clean. It may contain a number of pollutants that can be harmful to living things and the environment. It is important to understand how these pollutants are produced and how they can be prevented from contaminating the air.

LEARNING OBJECTIVES ✓ Describe chemical tests for the presence of water using anhydrous cobalt(II) chloride and anhydrous copper(II) sulfate. ✓ Describe how to test for the purity of water using melting point and boiling point. ✓ Explain that distilled water is used in practical chemistry rather than tap water because distilled water contains fewer chemical impurities. ✓ State that water from natural sources may contain substances, including: dissolved oxygen; metal compounds; plastics; sewage; harmful microbes; nitrates from fertilisers; phosphates from fertilisers and detergents. ✓ State that some of these substances are beneficial, including: dissolved oxygen for aquatic life; some metal compounds provide essential minerals for life.

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KNOWLEDGE CHECK ✓ Oxygen is present in the air and forms oxides when substances burn in it. ✓ Oxides of non-metals are acidic. ✓ Salts can be anhydrous or hydrated.

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∆ Fig. 10.2 Chemical test for water.

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WATER The test for water is to add it to anhydrous copper(II) sulfate solid. If the liquid contains water, the powder will turn from white to blue as hydrated copper(II) sulfate forms.

The equation for the reaction is: anhydrous copper(II) sulfate + water → hydrated copper(II) sulfate CuSO4(s) + 5H2O(l) → CuSO4 • 5H2O(s) The presence of water can also be detected using anhydrous cobalt(II) chloride. The pink anhydrous cobalt(II) chloride turns to blue hydrated cobalt(II) chloride. A convenient way of performing the test is to use cobalt(II) chloride paper: anhydrous cobalt(II) chloride + water → hydrated cobalt(II) chloride CoCl2(s) + 6H2O(l) → CoCl2 • 6H2O(s)

WATER

✓ State that some of these substances are potentially harmful, including: some metal compounds are toxic; some plastics harm aquatic life; sewage contains harmful microbes which cause disease; nitrates and phosphates lead to deoxygenation of water and damage to aquatic life. ✓ Describe the treatment of the domestic water supply in terms of: sedimentation and filtration to remove solids; use of carbon to remove tastes and odours; chlorination to kill microbes. ✓ State that ammonium salts and nitrates are used as fertilisers. ✓ Describe the use of NPK fertilisers to provide the elements nitrogen, phosphorus and potassium for improved plant growth. ✓ State the composition of clean, dry air as approximately 78% nitrogen, N2, 21% oxygen, O2, and the remainder as a mixture of noble gases and carbon dioxide, CO2. ✓ State the source of each of these air pollutants: carbon dioxide; carbon monoxide and particulates; methane; oxides of nitrogen; sulfur dioxide. ✓ State the adverse effects of these air pollutants: carbon dioxide; carbon monoxide; particulates; methane; oxides of nitrogen; sulfur dioxide. ✓ State and explain strategies to reduce the effects of climate change and acid rain. ✓ Describe photosynthesis as the reaction between carbon dioxide and water to produce glucose and oxygen in the presence of chlorophyll and using energy from light. ✓ State the word equation for photosynthesis: carbon dioxide + water → glucose + oxygen ✓ SUPPLEMENT Describe how the greenhouse gases carbon dioxide and methane cause global warming, limited to: the absorption, reflection and emission of thermal energy; reducing thermal energy loss to space. ✓ SUPPLEMENT Explain how oxides of nitrogen form in car engines and describe their removal by catalytic converters: e.g. 2CO + 2NO → 2CO2 + N2 ✓ SUPPLEMENT State the symbol equation for photosynthesis: 6CO2 + 6H2O → C6H12O6 + 6O2

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Neither of these tests shows the water is pure – only that the liquid has water in it.

Testing the purity of water There are several ways to check the purity of water, but the simplest way is to heat the water to boiling point and measure the boiling point.

Under normal atmospheric pressure pure water will boil at 100 oC. If the boiling point is lower or higher than this the water contains impurities. Another approach is to find the freezing point of the water, but this is not as simple to perform. Under normal atmospheric pressure pure water will freeze at 0 oC. Mixtures boil and freeze (or melt) over a range of temperatures.

You will be well aware that the water used in practical chemistry is distilled water. As the name suggests this is made by distilling a sample of water, possibly obtained from the domestic water supply. A simple distillation apparatus is shown in Fig. 12.11. The distilled water may not be absolutely pure but it will contain fewer chemical impurities.

The water cycle The recirculation of water that takes place all over the Earth is called the water cycle. water droplets in clouds become large enough to fall as rain

water vapour condenses to form clouds

water evaporates

∆ Fig. 10.3 The water cycle.

The pattern of rainfall over the planet determines where there are deserts, rainforests and areas of land that can or cannot be used for growing plants.

Much of the water we use on a daily basis is obtained from natural sources such as reservoirs, rivers or the sea. In countries where water is obtained from the sea desalination plants are used to remove salt (sodium chloride) from the water. This process is most successful in hot climates where the sea water evaporates and the condensation produced is collected.

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CHEMISTRY OF THE ENVIRONMENT

rivers and streams flow back to the sea

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The variety of substances often found in natural sources of water are shown in the table below.

Substances found in Advantages for the natural sources of water water supply dissolved oxygen supports fish and other aquatic life metal compounds can provide a source of essential minerals plastics sewage/ microbes nitrates (from fertilisers) and phosphates (from fertilisers and detergents)

Disadvantages for the water supply

some metal compounds are toxic very small plastic particles are harmful to all animals sewage contains harmful microbes that can cause disease these can lead to deoxygenation of the water and therefore damage to aquatic life

∆ Table 10.1 Substances found in natural sources of water.

∆ Fig. 10.4 Plastic pollution in an aquatic environment.

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∆ Fig. 10.5 Water pipes discharging.

WATER

Water is essential for life on Earth, and the demand for drinking water is increasing as the world’s population grows. Twothirds of the water is used in homes for washing, cleaning, cooking and in toilets. The rest is used by industry. Most industrial processes use water either as a raw material or for cooling. For example, it takes 200 000 litres of water to make 1 tonne of steel.

Water stored in reservoirs must be purified to produce drinkable tap water.

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Chlorine is passed through to kill bacteria.

Water supply to homes and industry.

▲

Water is filtered through beds of fine gravel and sand to remove small particles.

▲

Water is filtered through coarse gravel to remove larger pieces of dirt.

▲

▲

Water from reservoirs goes to a water treatment plant. Some sediments will settle to the bottom of the reservoir.

In addition, tap water in certain areas is treated with carbon to remove tastes and odours.

In certain parts of the world supplies of water are very limited. There is insufficient clean water to drink and not enough water to irrigate and support the growth of crops. Water that is not purified can often contain harmful bacteria and so is not safe to drink. In the absence of clean water people have little choice but to drink contaminated water and risk illness or death.

∆ Fig. 10.6 Ammonium nitrate fertiliser being sprayed onto a field. In some parts of the world, liquid ammonia is pumped directly into the ground as a fertiliser. This can be quite dangerous because liquid ammonia can cause chemical burns and irritate the respiratory tract.

∆ Fig. 10.7 Excess phosphate and nitrate nutrients in river water cause accelerated growth of green algae. The algae form a thick surface layer, which causes underwater plants and fish to die. Increased algal growth in the sea near river estuaries is also of concern.

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FERTILISERS The nitrogen in the soil can easily be used up by plants, for example when farmers are growing crops. Additional nitrogen can be added to the soil by using artificial fertilisers. Most of the nitrogen-containing artificial fertilisers are either nitrates or ammonium compounds. Other vital nutrients such as phosphorus (in the form of phosphates, which helps root growth) and potassium (in the form of potassium nitrate, which encourages flower and fruit formation) are often included with the nitrogen in what are called NPK fertilisers.

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Note: In the soil, ammonium compounds are converted first to ammonia and then to nitrates by bacteria. In the laboratory, ammonium compounds can be converted into ammonia by heating with an alkali such as sodium hydroxide.

AIR QUALITY AND CLIMATE Clean air is a mixture of gases. Its current composition is shown in Fig. 10.8. There are concerns about the effect of the increasing levels of carbon dioxide which is linked to increased global warming.

Nitrogen 78% Oxygen 21% Argon 0.9% Carbon dioxide 0.04% Trace amounts of other noble gases and water vapour 0.06%

∆ Fig. 10.8 Components of air.

iron filings air

water

Observing, measuring and recording 1. Predict what changes you would expect to see in the iron filings that were put in the tube at the beginning of the experiment.

Interpreting observations and data 2. State what chemical reaction was taking place in the tube? Write a balanced equation for the reaction.

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AIR QUALITY AND CLIMATE

∆ Fig. 10.9 Apparatus for experiment.

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Developing practical skills A student set up the apparatus as shown in Fig. 10.9 with the long tube turned upside-down in a trough of water. Previously some iron filings had been sprinkled into the tube, and many of these had stuck to the inside of the tube. With the same levels of water in the tube and the trough, the student recorded the volume of air in the tube (100 cm3).

After a few days he returned to the apparatus, equalised the water levels as before and took a second reading of the volume of air in the tube (85 cm3). He then worked out how much of the air had been replaced by water.

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3. Explain what the results indicate about the composition of the air in

the tube.

Evaluating methods 4. The results in this experiment are different to those obtained by other students. Suggest some possible reasons for this.

5. Explain why the student equalised the water levels in the trough and the tube before taking the reading of the volume of gas in the tube.

● SCIENCE IN CONTEXT

THE MANUFACTURE OF OXYGEN AND NITROGEN nitrogen gas out

Oxygen, nitrogen and the noble gases can all be manufactured from the air. The industrial process has several stages.

−190 °C

1. The air is cooled to about −80 °C so that carbon dioxide and water vapour solidify and can be removed.

liquefied air in at −200 °C

2. The air is cooled further, compressed and then allowed to expand quickly. This causes further cooling, and at about −200 °C the air becomes a liquid.

3. The liquid air is fractionally distilled. This involves using a large fractionating column which separates liquids with different boiling points. Oxygen’s boiling point is −183 °C and nitrogen’s is −196 °C: so they can be separated.

−185 °C

liquid oxygen out ∆ Fig. 10.10 Fractional distillation of liquid air.

Oxygen is used in medicine to support patients with breathing difficulties. It is also mixed with hydrocarbons such as ethyne (acetylene) for use in cutting tools.

Nitrogen’s uses depend on its very low reactivity. It is used in food packaging as a way of excluding air and stopping oxidation and decay.

It is also used to reduce fire hazards, particularly in military aircraft fuel systems.

Challenge Question: Explain why oxygen is a liquid at –185 oC and nitrogen is a gas at –190 oC.

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Oxygen and nitrogen are stored in large metal cylinders under high pressure and remain as liquids until the pressure is released.

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The processes affecting the composition of the air can be illustrated in the carbon cycle.

The carbon cycle photosynthesis carbon dioxide in the atmosphere respiration

respiration

plants

respiration

combustion

eaten death

animals death, excretion decomposition decomposers organic wastes

fossil fuels

gas oil coal white arrows indicate change over millions of years

∆ Fig. 10.11 The carbon cycle.

QUESTIONS 1. Define the term anhydrous.

2. State what colour change you would observe if water is added to anhydrous cobalt(II) chloride.

3. Explain how you could test for the purity of a sample of water.

4. In the purification of water there are two important stages: a) In the first stage, the water is filtered twice. State what is used as the filter in each case.

b) In the second stage, bacteria are killed. State which chemical is used to kill the bacteria.

a) State the percentage of nitrogen in clean air. b) State the percentage of carbon dioxide in clean air.

6. In the carbon cycle, give the name of a process that removes

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carbon dioxide from the atmosphere.

AIR QUALITY AND CLIMATE

5. This question is about the composition of the air.

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Pollutants in the air Pollutants in the air come from a variety of sources. Some come from burning waste and some from power stations burning coal or gas.

Industry produces pollutants as well.

The most common pollutants in the air are: • Carbon dioxide from the complete combustion of carbon-containing fuels. The increased levels of carbon dioxide result in global warming and climate change.

• Carbon monoxide and particulates from the incomplete combustion of carbon-containing fuels, for example, hydrocarbons (petrol/coal/ gas/diesel). Carbon monoxide is a highly toxic and dangerous gas.

Particulates increase the risk of respiratory problems and cancer.

• Methane from the decomposition of vegetation and waste gases from digestion in animals. Higher levels of methane lead to increasing global warming and climate change.

• Oxides of nitrogen from car engines. They contribute to the formation of acid rain, photochemical smog and respiratory problems.

• Sulfur dioxide from the combustion of fossil fuels that ∆ Fig. 10.12 Cycling is encouraged in Amsterdam to reduce contain sulfur compounds, for air pollution. example, petrol and coal. Sulfur dioxide is a major source of acid rain.

How is the atmosphere changing and why?

Climate change is a huge issue facing all parts of the world.

The greenhouse effect Carbon dioxide, methane and CFCs (chlorofluorocarbons) are known as greenhouse gases. The levels of these gases in the atmosphere are increasing due to the burning of fossil fuels, pollution from farm animals and the use of CFCs in aerosols and refrigerators.

Short-wave radiation from the Sun warms the ground, and the warm Earth emits thermal energy as long-wave radiation. Much of this radiation is stopped from escaping from the Earth by absorption and reflection. This reduction of thermal energy loss to space is known as the greenhouse effect.

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SUPPLEMENT

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The greenhouse effect is responsible for keeping the Earth warmer than it would otherwise be. This is known as global warming. If global warming continues the Earth’s climate will change, polar ice will continue to melt and sea levels will continue to rise resulting in serious flooding of low-lying areas – some of them highly populated.

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Global atmospheric CO2 concentration

CO2 concentration (parts per million)

400 380 360 340 320 300 280 260 1750

1780

1810

1840

1870

1900

1930

1960

1990

2020

Year Global temperature change 1.2

Temperature change (°C)

1.0 0.8 0.6 0.4 0.2 0.0 –0.2 1850

1875

1900

1925

1950

1975

2000

2025

Year

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Acid rain Burning fossil fuels gives off many gases, including sulfur dioxide and various nitrogen oxides: sulfur + oxygen → sulfur dioxide S(s) + O2(g) → SO2(g)

AIR QUALITY AND CLIMATE

∆ Fig. 10.13 How atmospheric carbon dioxide and global temperature have changed over time.

Global temperature change is relative to temperatures in the pre-industrial period, 1850–1900.

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Sulfur dioxide combines with water and oxygen to form sulfuric acid.

Nitrogen oxide combines with water to form nitric acid. These substances can make the rain acidic (called acid rain). sulfur dioxide + oxygen + water → sulfuric acid + O2(g) + 2H2O(l) → 2H2SO4(aq) 2SO2(g) Buildings are damaged by acid rain, particularly those made of limestone and marble – both are forms of calcium carbonate, CaCO3.

Metal structures are also attacked by sulfuric acid.

Acid rain harms plants that take in the acidic water and harms the animals that live in the affected rivers and lakes. Acid rain also washes ions such as calcium and magnesium out of the soil, depleting the minerals available to plants. It also washes aluminium ions out of the soil and into rivers and lakes, where they poison fish.

Nitrogen monoxide can be oxidised to a brown gas called nitrogen dioxide, NO2. Under certain atmospheric conditions this can build up as a brown haze in large cities. Nitrogen dioxide is dangerous because it can cause respiratory diseases such as bronchitis.

Reducing emissions of the gases that cause acid rain is expensive. Part of the problem is that the acid rain usually falls a long way from the places where the gases were released.

Power stations are now being fitted with flue-gas desulfurisation plants (FGD) which use calcium oxide to reduce the amount of sulfur dioxide released into the atmosphere.

Catalytic converters are fitted to the exhaust systems of vehicles to reduce the level of pollutants released from burning petrol or diesel.

CO2, SO2, NOx etc.

eruption of volcanic material releasing hydrogen sulfide acids are incorporated into clouds

hydrogen sulfide from hot springs

SO2 various reactions lead to the formation of acids NOx

precipitation

wet deposition can be carried many miles from the source before being deposited

precipitation dimethyl sulfide from the decomposition of plankton

dry deposition falls close to the pollution source 1–2 km 100s to 1000s km

∆ Fig. 10.14 The process of the formation of acid rain.

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emissions

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Reducing the effects of climate change and acid rain Steps are being taken to reduce the effects of environmental issues.

These are summarised in the table below.

Environmental issues Climate change

Acid rain

Action being taken • increasing the use of hydrogen as a fuel • increasing the production of renewable energy using wind and solar power • planting trees to reduce the level of carbon dioxide by photosynthesis • reducing the use of fossil fuels • reduction in livestock farming to reduce methane production • increasing the use of catalytic converters in vehicles • reducing emissions of sulfur dioxide by using lowsulfur fuels and flue-gas desulfurisation with calcium oxide

∆ Table 10.2 Reducing the effects of climate change and acid rain.

SUPPLEMENT

Under normal conditions nitrogen is a very unreactive gas. However, in a petrol engine temperatures of 1000 °C can be reached, and in these conditions nitrogen reacts with oxygen to make oxides of nitrogen.

Nitrogen oxides are often represented by NOx, but they are mainly nitrogen monoxide, NO. A catalytic converter in the car’s exhaust system can convert the nitrogen oxides back to nitrogen: 2NO(g) + 2CO(g) → N2(g) + 2CO2(g) Rhodium is frequently used as a catalyst in catalytic convertors.

● SCIENCE IN CONTEXT

SOME INTERESTING FACTS ABOUT METHANE

3. Biogas contains 40–70% methane. Biodigesters convert organic wastes into a nutrient-rich liquid fertiliser and biogas, a renewable source of electrical and heat energy. These are widely used in countries such as India, Nepal and Vietnam. Biodigesters can help families by providing a cheap source of fuel, reducing environmental pollution from the run-off from animal pens, and reducing diseases caused by the use of untreated manure as fertiliser.

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2. It is formed by the decay of plant matter where there is no oxygen (anaerobic decay).

AIR QUALITY AND CLIMATE

1. Methane makes up about 97% of natural gas.

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∆ Fig. 10.15 A commercial biodigester.

4. Methane is one of the greenhouse gases responsible for global warming. It has almost 25 times the effect of the same volume of carbon dioxide.

5. Ruminant animals such as cows and sheep produce methane. It has been estimated that a cow can produce as much as 200 litres of methane per day.

Challenge Question: It seems highly likely that cows are one of the causes of global warming, Discuss the issues this raises for the world.

SUPPLEMENT

The symbol equation for photosynthesis is shown below. Chlorophyll and energy from the Sun are both crucial for this reaction.

6CO2(g) + 6H2O(l) → C6H12O6(aq) + 6O2(g)

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Photosynthesis Photosynthesis is an important process for plants but also for reducing the level of carbon dioxide in the atmosphere. In the presence of chlorophyll and using energy from light, carbon dioxide reacts with water to produce glucose. carbon dioxide + water → glucose + oxygen

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QUESTIONS 1. Carbon monoxide is a common pollutant in the air. Give a major source of the carbon monoxide.

2. a) Methane is a greenhouse gas. Give two sources of methane. b) Give the name of another greenhouse gas.

3. a) Give the name of two gases that are responsible for causing acid rain.

b) For each gas you named in part a) give the name of the acid it forms.

c) Suggest three problems caused by acid rain in the environment.

4. SUPPLEMENT Nitrogen monoxide (NO) is produced from nitrogen and oxygen in the high temperature of a car engine.

a) Write a balanced equation to show how the nitrogen monoxide is formed.

b) Nitrogen monoxide and carbon monoxide are converted in a catalytic converter. Write an equation for this reaction.

5. SUPPLEMENT Write a symbol equation for the production of

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AIR QUALITY AND CLIMATE

glucose by photosynthesis.

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End of topic checklist Key terms acid rain, combustion, climate change, fossil fuel, global warming, greenhouse effect, greenhouse gas, particulates, photochemical smog, photosynthesis, renewable energy

During your study of this topic you should have learned:

❍ How to describe chemical tests for identifying the presence of water using anhydrous cobalt(II) chloride and anhydrous copper(II) sulfate.

❍ That the melting and boiling points of a water sample can be used to test its purity. ❍ That distilled water is used in practical chemistry rather than tap water as it contains fewer chemical impurities.

❍ That water from natural sources could contain: dissolved oxygen, metal

compounds, plastics, sewage, harmful microbes, nitrates from fertilisers and phosphates from fertilisers and detergents.

❍ That oxygen dissolved in water is good for aquatic life and some metal compounds in water provide essential minerals.

❍ That some metal compounds in water are toxic, some plastics harm aquatic life,

sewage contains microbes which cause disease, and nitrates and phosphates lead to deoxygenation.

❍ How to describe in outline the treatment of the domestic water supply in terms of sedimentation, use of carbon and chlorination.

❍ That ammonium salts and nitrates are used as fertilisers and NPK fertilisers contain nitrogen, phosphorus and potassium.

❍ That clean dry air is approximately 78% nitrogen and 21% oxygen with the ❍ That common pollutants in the air are carbon dioxide (from complete combustion

of carbon-containing fuels), carbon monoxide and particulates (from incomplete combustion of carbon-containing fuels), methane (from decomposition of vegetation and waste gases from animal digestion), sulfur dioxide (from combustion of sulfur-containing fossil fuels) and oxides of nitrogen (from car engines).

❍ That higher levels of carbon dioxide and methane lead to increased global warming and climate change.

❍ That carbon monoxide is a toxic gas and particulates increase the risk of respiratory problems and cancer.

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remainder made up of a mixture of noble gases and carbon dioxide.

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❍ That sulfur dioxide and oxides of nitrogen cause acid rain. ❍ That the oxides of nitrogen also cause photochemical smog and respiratory problems.

❍ That climate change can be reduced by planting trees, reducing livestock farming,

decreasing use of fossil fuels and increasing use of hydrogen and renewable energy.

❍ That acid rain can be reduced by using catalytic converters, using low-sulfur fuels and flue-gas desulfurisation with calcium oxide.

❍ That photosynthesis involves the reaction:

carbon dioxide + water → glucose + oxygen in the presence of chlorophyll and energy from light.

❍ SUPPLEMENT How the greenhouse gases carbon dioxide and methane absorb and reflect thermal energy and so reduce heat loss to space.

❍ SUPPLEMENT How to explain the removal of oxides of nitrogen by catalytic converters.

❍ SUPPLEMENT That the symbol equation for photosynthesis is:

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6CO2 + 6H2O → C6H12O6 + 6O2

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End of topic questions Note: The marks awarded for these questions indicate the level of detail required in the answers. In the examination, the number of marks awarded to questions like these may be different.

1. State which one of the following substances found in natural sources of water is NOT harmful.

A dissolved oxygen B sewage C nitrates D phosphates

(1 mark)

2. Explain why distilled water is used in practical chemistry rather than tap water.

(1 mark)

3. a) State what you could use to detect the presence of water.

(1 mark)

b) State what you would observe if water was present.

(2 marks)

4. Discuss what problems fertilisers such as nitrates and phosphates can cause in (2 marks) streams and rivers.

5. In the purification of domestic water supplies state what chemical can be used to (1 mark) kill microbes.

6. This question is about the composition of a sample of clean, dry air. a) State the proportion of oxygen.

(1 mark)

b) State the proportion of carbon dioxide.

(1 mark)

Pollutant Lead compounds Carbon monoxide Sulfur dioxide Oxides of nitrogen

What is the source of the pollutant?

Lead additives in petrol

How does the pollutant get into the air?

Burning petrol in a car

(6 marks)

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7. The table shows some of the pollutants found in air. For each pollutant identify the source of the pollution and how it gets into the air. The first one has been done for you.

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8. Copy and complete the following table to explain some of these important chemical processes.

Process

What is removed from the air in the process?

What is put into the air in the process?

Combustion Respiration Photosynthesis (6 marks)

9. SUPPLEMENT This question is about the greenhouse effect. a) Explain what the greenhouse effect is.

(2 marks)

b) Give the names of two greenhouse gases.

(2 marks)

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10. SUPPLEMENT Explain how oxides of nitrogen formed in car engines can be removed by catalytic converters.

(2 marks)

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