Chapter 26Pollution 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;
Chapter 26PollutionLEARNING 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.
Chapter 26PollutionEnvironment 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) environmentand the living (biotic) environment.
Chapter 26PollutionComposition of air The noble gases consist mainly of argon and minuteamounts of helium, neon, krypton and xenon. Clean air also contains varying amounts of water vapour.
Chapter 26PollutionSeparation 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?
Chapter 26PollutionUses 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.
Chapter 26PollutionWhen substances containing carbon burn inoxygen, 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
Chapter 26PollutionQuick check 11. (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
Chapter 26PollutionSolution to Quick check 11. (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
Chapter 26Pollution 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.
Chapter 26Pollution 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
Chapter 26PollutionCarbon 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.
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.
Chapter 26PollutionLead 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.
Chapter 26PollutionSulphur 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.
Chapter 26PollutionNitrogen 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.
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.
Chapter 26PollutionChlorofluorocarbons (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.
Chapter 26PollutionMethane 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.
Chapter 26PollutionQuick check 21. 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
Chapter 26PollutionSolution to Quick check 21. (a) Non-acidic: ozone, methane (b) Acidic pollutants: sulphur dioxide, nitrogen dioxide2. (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 dioxide3. (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
Chapter 26PollutionAcid 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.
Chapter 26PollutionHarmful 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.
Chapter 26PollutionPrevention 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 withcalcium hydroxide. Calcium sulphite and water are formed in the process. SO2(g) + Ca(OH)2(s) CaSO3(s) + H2O(l)
Chapter 26PollutionControlling 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)
Chapter 26PollutionReducing 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.
Chapter 26PollutionReducing 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.
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 formationGround level Unburnt hydrocarbons Irritates eyes, throat and Fit catalytic converters to cars, ozone and NO2 lungs; asthma attacks reduce vehicle population
Chapter 26 PollutionQuick check 31. 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
Chapter 26 PollutionSolution to Quick check 31. (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.