1. Chapter 26
Pollution
LEARNING OUTCOMES
Define the term environment;
Define the terms pollution and pollutant;
Identify common sources of pollution;
Describe the effects of pollutants on the environment;
Discuss the harmful effects of non-metal and metal
compounds to living systems and the environment;
Distinguish among biodegradable, recyclable and toxic
solid household waste;
Evaluate the methods used for solid waste disposal;

2. Chapter 26
Pollution
LEARNING OUTCOMES
Relate the unique properties of water to its functions in living systems;
Discuss the consequences of the solvent properties of water;
Describe the methods used in the treatment of water for domestic purposes;
Discuss the need for managing and preserving the environment;
Discuss the ways for managing and preserving the environment.

3. Chapter 26
Pollution
Environment
 The conditions around an organism which affect its growth,
development and survival make up the environment of the organism.
The environment is made up of the physical (abiotic) environment
and the living (biotic) environment.

4. Chapter 26
Pollution
Composition of air
 The noble gases consist mainly of argon and minute
amounts of helium, neon, krypton and xenon.
 Clean air also contains varying amounts of water vapour.

5. Chapter 26
Pollution
Separation of gases in air
 Air is cooled under high pressure until it becomes a liquid at
around -200 oC.
 The liquid air is then fractionally distilled to separate into
liquid nitrogen, liquid oxygen and noble gases.
Pause and Think
The boiling point of liquid oxygen is -183 oC and liquid
nitrogen is -196 oC. Which gas will be the first to be
distilled when liquid air at - 200 oC is warmed up?

6. Chapter 26
Pollution
Uses of oxygen
 Liquid oxygen is used for burning fuels in
rockets.
 Oxygen is used in the oxy-acetylene flame for
welding and cutting iron and steel.
 In the manufacture of steel, pure oxygen is
blown into molten iron to burn away the
impurities.
 Oxygen is used by patients in hospitals who
have difficulty in breathing, by deep sea divers,
by airplane pilots, mountaineers and
astronauts.

7. Chapter 26
Pollution
When substances containing carbon burn in
oxygen, any of these two can take place:
 Complete combustion
 This occurs when there is sufficient oxygen.
 The products are carbon dioxide and water.
E.g. CH4 + 2O2  CO2 + 2H2O
 Incomplete combustion
 This occurs when there is insufficient oxygen.
 The products are carbon dioxide, water, carbon
monoxide and soot.
E.g. 4CH4 + 5O2  2CO + 8H2O + 2C

8. Chapter 26
Pollution
Quick check 1
1. (a) How is oxygen obtained from the air in the industry?
(b) State two commercial uses of oxygen.
2. Acetylene is used in the oxy-acetylene flame for cutting and welding
metals. It has the formula C2H2.
(a) Construct the equation for the complete combustion of acetylene.
(b) What will happen if there is an insufficient supply of oxygen?
3. (a) What is the difference between combustion and burning?
(b) What is the difference between respiration and
photosynthesis?
Solution

9. Chapter 26
Pollution
Solution to Quick check 1
1. (a) Oxygen is obtained from the industry by the fractional distillation of liquid air.
(b) (i) Oxygen is used in oxy-acetylene flames for cutting metal.
(ii) Oxygen is used by deep-sea divers and mountaineers.
2. (a) 2C2H2 + 5O2  4CO2 + 2H2O
(b) If there is an insufficient supply of oxygen, combustion will be
incomplete and carbon monoxide and soot will be formed.
3. (a) Combustion is an exothermic reaction between a substance
and oxygen with or without flames. Burning is combustion
accompanied by the presence of flames.
(b) Respiration is a process by which oxygen is taken in by
living things to oxidise food into carbon dioxide, water and energy.
Photosynthesis is a process by which green plants take in
carbon dioxide and water with the help of sunlight to make
carbohydrates, releasing oxygen in the process.
Return

10. Chapter 26
Pollution
Air Pollution
 The air we breathe in may not be clean. It
may be polluted by substances called
pollutants.
 Pollutants are harmful substances that have
undesirable effects on people and the
environment.

11. Chapter 26
Pollution
The main air pollutants are:
Air Pollution ► Carbon monoxide (CO)
► Carbon dioxide (CO2)
► Lead compounds
► Sulphur dioxide (SO2)
► Nitrogen oxides (NO, NO2)
► Ozone (O3) at ground level
► Chlorofluorocarbons (CFCs)
► Methane (CH4)
► Unburned hydrocarbons

12. Chapter 26
Pollution
Carbon monoxide (CO)
 Carbon monoxide comes from forest fires, incomplete
combustion of fuels in motor vehicles, factories and power
stations.
 Carbon monoxide reacts with the haemoglobin in red blood cells
to form carboxyhaemoglobin, reducing the blood’s ability to
absorb oxygen. Small quantities of carbon monoxide cause
headaches and breathing difficulties, larger quantities cause
heart damage and death.
 Carbon monoxide is dangerous as it is colourless and odourless
and thus gives no warning of its presence.

13. Chapter 25
Pollution
Carbon dioxide
 Carbon dioxide occurs naturally in the air and makes up
about 0.03% of the air. It is used by plants for
photosynthesis. Oxygen is released during
photosynthesis, and so there is a balance in nature which
maintains the amounts of carbon dioxide and oxygen in
the atmosphere.
 However, the level of carbon dioxide has been increasing
rapidly over the last 50 years due to industrialisation and
urbanisation which resulted in the accelerated burning of
fossil fuels and clearing of forests.
 Carbon dioxide is a greenhouse gas which contributes to
global warming.
 Global warming leads to drastic weather changes, such as
extreme droughts in some parts and heavy rain in other
parts of the world. Global warming has caused the melting A battered Earth
of the polar ice caps and will eventually cause flooding to
many coastal regions of the world.

14. Chapter 26
Pollution
Lead compounds
 Lead particles in the air come mainly from exhaust
fumes emitted because of the combustion of leaded
gasoline in motor vehicles.
 Lead poisoning may lead to brain damage, especially in
infants. It has also been reported that lead is one of the
main causes of forest decline.

15. Chapter 26
Pollution
Sulphur dioxide (SO2)
 Sulphur dioxide comes from the burning of fuels like
coal and fuel oil in factories and power stations.
 When these fuels burn, the sulphur in the fuel is
oxidised into sulphur dioxide:
S + O2  SO2
 Some sulphur dioxide comes from volcanic eruptions.
 Sulphur dioxide causes eye irritation, breathing difficulties
and asthma attacks.
 Sulphur dioxide causes the formation of acid rain.

16. Chapter 26
Pollution
Nitrogen oxides (NOx)
 Nitrogen monoxide is produced when nitrogen combines
with oxygen at high temperatures, such as during
lightning storms and inside the engines of motorcars.
N2 + O2  2NO
 The nitrogen monoxide then combines with more
oxygen to form nitrogen dioxide:
2NO + O2  2NO2
 Nitrogen oxides cause breathing difficulties and
lung damage.
 Nitrogen oxides react with unburned hydrocarbons to form
ground level ozone and photochemical smog.
 Nitrogen dioxide reacts with atmospheric oxygen
and water to form acid rain.

17. Chapter 26
Pollution
Ozone
 A layer of ozone surrounds the Earth at high
altitudes and protects us from the harmful
radiation of the Sun.
 However, at ground level, ozone is a
harmful pollutant that causes irritation
to the eyes and throat. It also causes
breathing difficulties and asthma attacks.
 Most of the ozone is produced by the action of
sunlight on nitrogen dioxide and unburned
hydrocarbons. In heavily polluted cities it forms
photochemical smog.

18. Chapter 26
Pollution
Chlorofluorocarbons (CFCs)
 Most of these compounds are used as
solvents, coolant gases in refrigerators
and for making plastics.
 CFCs destroy the ozone layer that
protects our Earth from ultraviolet Cause hole in
radiation from the Sun. ozone layer
 Pollution from CFCs can be
reduced by banning their use in
aerosol sprays and refrigerators.

19. Chapter 26
Pollution
Methane
 Small amounts of methane are present
naturally in the atmosphere due to the decay
of vegetation and animals.
 However, increasingly large amounts
of methane are produced because of
agriculture, mining activities and
rearing of livestock such as cows.
 Methane causes the “greenhouse effect”
which traps the Sun’s heat and causes global
warming, leading to drastic climatic changes
and melting of the polar ice caps.

20. Chapter 26
Pollution
Quick check 2
1. Name two air pollutants that are
(a) non-acidic,
(b) acidic.
2. Name the air pollutants that are released into
the atmosphere by the following:
(a) volcanic eruptions, (b) decay of vegetation,
(c) forest fires, (d) motorcars.
3. (a) What is the chemical formula of ozone?
(b) How is ozone
(i) useful
(ii) harmful?
(c) Describe how ground level ozone is produced. Solution

21. Chapter 26
Pollution
Solution to Quick check 2
1. (a) Non-acidic: ozone, methane
(b) Acidic pollutants: sulphur dioxide, nitrogen dioxide
2. (a) Volcanic eruptions: sulphur dioxide
(b) Decay of vegetation: methane
(c) Forest fires: carbon monoxide, carbon dioxide
(d) Motorcars: carbon monoxide, nitrogen oxides,
unburned hydrocarbons, carbon dioxide
3. (a) Formula of ozone: O3
(b) (i) Ozone is useful when it is high in the upper atmosphere where it protects the
Earth against the harmful UV radiation from the Sun.
(ii) At ground level, ozone is harmful because it causes irritation to the eyes
and throat and harms the lungs.
(c) Ground level ozone is produced when nitrogen oxides react with unburned
hydrocarbons under strong sunlight.
Return

22. Chapter 26
Pollution
Acid rain has a pH of
Acid

rain
between 1–5 compared to
normal rain water which
has a pH of about 5.6.
 Acid rain is rain that contains
a large proportion of acids
such as sulphuric acid and
nitric acid.
 When sulphur dioxide in the air reacts with oxygen and water, it forms sulphuric acid:
2SO2 + O2 + 2H2O  2H2SO4
 Nitrogen dioxide in the air reacts with oxygen and water to form nitric acid:
4NO2 + O2 + 2H2O  4HNO3
 These two acids dissolve in the rain water to form acid rain.

23. Chapter 26
Pollution
Harmful effects of acid rain
 Acid rain corrodes buildings, bridges, statues and other
structures made of metal or stone.
 Acid rain kills fishes in lakes and rivers.
 Acid rain kills plants and vegetation by damaging their
roots, leading to deforestation in many parts of the world,
like Canada and Europe.

24. Chapter 26
Pollution
Prevention of acid rain
 Use fuels with less sulphur content, e.g. natural gas instead of coal.
 Treat acidic waste gases from factories and power stations with calcium oxide
or calcium carbonate before releasing them into the air.
 Use catalytic converters in motor vehicles to reduce emissions of nitrogen
oxides.
Sulphur dioxide should be removed from waste gases by treating it with
calcium hydroxide. Calcium sulphite and water are formed in the process.
SO2(g) + Ca(OH)2(s)  CaSO3(s) + H2O(l)

25. Chapter 26
Pollution
Controlling air pollution
 Carbon monoxide can be reduced
by preventing forest fires and by
making sure than the combustion of
fuels is complete.
 Carbon monoxide and nitrogen
oxides can be reduced in
motorcars by fitting them with
catalytic converters which convert
the carbon monoxide into carbon
dioxide, and nitrogen oxide into
nitrogen.
2CO(g) + 2NO(g)  2CO2(g) + N2(g)

26. Chapter 26
Pollution
Reducing air pollution
 Sulphur dioxide can be reduced by
burning fuels with less sulphur content, for
example, by using natural gas instead of
coal in power stations.
 Sulphur dioxide and nitrogen dioxide can be reduced by treating the
waste gases from power stations and factories with calcium oxide or
calcium carbonate before releasing them into the atmosphere.
 Ozone pollution can be prevented by reducing the emissions of unburned
hydrocarbons from vehicles by installing catalytic converters, and by
decreasing the car population.

27. Chapter 26
Pollution
Reducing carbon dioxide
 Carbon dioxide is released whenever fossil fuels are burned. The
only way to reduce carbon dioxide is to burn less fossil fuels. This
can be done by making the combustion more “ carbon efficient” i.e.
producing more heat from a smaller quantity of fuel.
 Another way of reducing carbon dioxide emission is to use
alternative sources of energy, such as solar energy, hydroelectric
power and wind energy.

28. Chapter 26
Pollution
Summary
Pollutant Source Harmful Effects Prevention
Carbon Incomplete combustion Headaches, breathing Fit catalytic converters to cars
monoxide of fossil fuels difficulties, heart damage,
death
Sulphur Combustion of fossil Breathing difficulties, asthma Treat waste gases with calcium
dioxide fuels attacks, acid rain oxide, fit catalytic converters to cars
Nitrogen Lightning, vehicle Breathing difficulties, acid Fit catalytic converters to cars
oxides engines rain, ozone formation
Methane Decay of vegetation, Global warming, ozone Improve diets of cattle
cows formation
Ground level Unburnt hydrocarbons Irritates eyes, throat and Fit catalytic converters to cars,
ozone and NO2 lungs; asthma attacks reduce vehicle population

29. Chapter 26
Pollution
Quick check 3
1. Describe how the following pollutants can be eliminated or reduced:
(a) carbon monoxide,
(b) nitrogen oxides,
(c) sulphur dioxide,
(d) unburned hydrocarbons.
2. (a) State the gases which cause acid rain and describe how these
acids are formed by the named gases.
(b) State two harmful effects of acid rain.
(c) State two ways of reducing acid rain.
Solution

30. Chapter 26
Pollution
Solution to Quick check 3
1. (a) carbon monoxide: Prevent forest fires, install catalytic converters in motorcars;
(b) nitrogen oxides: treat waste gases from factories and power stations with calcium
oxide, install catalytic converters in motorcars;
(c) sulphur dioxide: use natural gas instead of coal in power stations, treat waste
gases from factories and power stations with calcium oxide;
(d) unburned hydrocarbons: install catalytic converters in motorcars.
2. (a) Acid rain is caused by the presence of sulphuric and nitric acids in the rain.
Sulphuric acid and nitric acid are formed when sulphur dioxide and nitrogen
dioxide react with oxygen and water in the atmosphere respectively as follows:
2SO2 + O2 + 2H2O  2H2SO4
4NO2 + O2 + 2H2O  4HNO3
(b) Acid rain destroys stone buildings and statues, kills plants and causes Return
deforestation.
(c) Acid rain can be reduced by removing sulphur dioxide and nitrogen oxides from
waste gases by treating them with calcium oxide. Avoid the burning of coal and
fuel oil that contains large amounts of sulphur.