The Air Around Us
Post on 21-Jul-2016
THE AIR AROUND US
COMPOSITION OF AIR
1. Our Earth is surrounded by a layer of air called the atmosphere.2. The atsosphere protects living things on the Earth harmful rays from the sun.3. Air is colourless, tasteless and odourless (no smell).4. We cannot see air but can feel it when it moves as a wind.5. Air is a mixture of many components.
6.Nitrogen(a) Nitrogen is a very inactive gas.(b) Nitrogen does not burn and does not support combustion i.e it does not allow things to burn ini it.(c) Nitrogen dilutes oxygen in the air so that processes such as respiration, burning and decay go on more slowly.7. Oxygen(a) Oxygen is used up during:i- respirationii- burningiii- decayiv- rusting(b) Oxygen is needed for living things to survive.(c) Oxygen is set free during the process of photosynthesis.8. Rare gases(a) The rare gases in air are:i- heliumii- neoniii- argoniv- kryptonv- xenonvi- radon(b) these gases are very incative but have their uses.9. Carbon dioxide(a) Carbon dioxide is set free during:i- respirationii- burningiii- decay(b) It is absorbed by green plants during photosynthesis10. Water vapour, dust and microorganisms(a) These things vary in air.(b) Most microorganisms in air are bacteria and spores from fungi.
PROPERTIES OF OXYGEN AND CARBON DIOXIDE
1. Oxygen is a colourless, odourless and tasteless gas.2. It is not very soluble in water.3. It is neutral when tested with moist litmus paper.4. It is slightly denser (heavier) than air.5. It is an extremely active element.6. It supports burning, breathing, decaying and rusting.7. it combines easily with many metals and non-metals.8. It does not burn by itself.
1. Carbon dioxide is a colourless, odourless gas with a slight acidic taste.2. It is denser (heavier) than air.3. It is slightly soluble in water.4. It does not burn by itself.5. It does not support combustion.6. It is very soluble in sodium hydroxide solution.7. It turns moist blue litmus paper to a faint red; hence, it is a weak acid.8. It turns lime water cloudly.
1. Oxygen and carbon dioxide have their specific properties.2. Gases in the air can be identified from their properties.3. The following experiment is carried out to study the properties of oxygen and carbon dioxide from certain aspects.
Confirmatory tests for oxygen and carbon dioxide are shown below.(a) Confirmatory test for oxygen
(b) Confirmatory test for carbon dioxide.
OXYGEN IS NEEDED IN RESPIRATION
1. Respiration is carried out in all living cells. It is a continuous process that takes place day and night.2. During respiration or breathing, oxygen is taken in from the air and carbon dioxide is released.3. Oxygen is needed for respiration. Oxygen is taken in to oxidise (burn away) the food in cells to produce energy. This process is called respiration.4. The term rspiration covers the breathing in and out of air and the use of oxygen in the body.5. Living things use oxygen and release carbon dioxide during respiration.6. Simple carbohydrates, e.g. glucose, are broken down by making use of the oxygen absorbed by the cells.7. Energy, carbon dioxide and water vapour are the by-products of respiration.
8. The following experiment shows that living things use oxygen and give out carbon dioxide.
1. In the process of breathing, air from the surroundings is inhaled or sucked into the lungs. This air is known as inhaled air.2. Air that is exhaled or breathed out from the lungs is known as exhaled air.
Breathing process3. The exhaled air of humans can be collected by breathing out air through a rubber tube into a container filled with water and overturned in water (method of water displacement) as shown in the figure below.
Collection of exhaled air
1. The quantities of nitrogen and rare gases in exhaled air stay unchanged i.e. 78% and 0.9% respectively.
2. The quantity of carbon dioxide in exhaled air is 4%, which is over a hundred times greater than normally present in the atmosphere.
3. Exhaled air is saturated with water vapour.
4. Exhaled air is warmer than ordinary air due to the release of energy during respiration.
OXYGEN AND COMBUSTION
1. Combustion is a chemical reaction which takes place when a substance combines with oxygen and produces:(a) an oxide(b) heat energy(c) light energyExamples:(a) Carbon dioxide, heat energy and light energy are produces when carbon burns in air.
(b) Magnesium oxide, heat energy and light energy are produced when magnesium burns in air.
2. When a hydrocarbon (a compound containing hydrogen and carbon only) such as a candle burns, the products are:(a) water(b) carbon dioxide(c) heat energy(d) light energy
3. The reactions in the above examples show that combustion needs oxygen. This can also be shown in the following ways:(a) i. If a gas jar of oxygen is inverted over a burning candle, the candle goes on burning until the oxygen it used up. ii. If a gas of nitrogen or carbon dioxide is inverted over a burning candle, the candle flame is extinguished at once.
(b) i. If two glass jars, one small and one big, are inverted over two similiar burning candles, the candle in the large jar burns longer. This is because the large jar contains more oxygen than the small jar.
(c) Combustion uses one-fifth of the air.
1. Materials which are easily burnt are called fuels.2. The fuels used come mainly from three materials, as given below.
3. Three conditions are required for combustion:(a) fuel(b) oxygen(c) heat.
4. Combustion cannot take place if one of these comditions is not fulfilled.5. The principle in fire fighting is to remove one of these factors from the fire.6. (a) Oxygen The supply of oxygen to a fire can be stopped by using a fire-extinguisher to spray foam or carbon dioxide on the fire. The foam or dense carbon dioxide surrounds the fire and prevents air (oxygen) from getting to it. (b) Fuel If a fire is caused by a gas, stopping the gas supply will put out the fire. For example, a Bunsen burner flame is extinguished when the gas tap is turned off. (c) Heat A fuel cannot burn if its temperature is not high enough. Water can extinguish a fire because it lowers the temperature of the fuel to below its ingition point i.e. below the temperature at which it burns.7. The method for extinguishing fire depends on the source of the fire.
Combustion plays a very important role in our everyday life.
1. Unwanted and harmful subtances are added to the air by factories, motor vehicles, forest fires, the development of large housing estates and the extensive use of chlorofluorocarbons.2. The addition of unwanted and harmful substances to the air is known as air pollution.3. The unwanted and harmful substances are called the pollutants.4. The air such as dust and sulphur dioxide harm our health and the environment.5. The air in industrial areas because there are more factories, motor vehicles and development projects going on in industrial areas.6. Air pollutants are due to man's activities.7. Man must control his activities so that they do not pollute the air, because clean air is essential for a healthy life.
The main air pollutants, their sources and effects are given in the table below.
1. Air pollution causes harmful effects on living things, including man and on the enviroment.2. Some of these harmful effects are explained below.3. Health problems(a) Harmful gases, dust and soot in the air cause several health problems such as: i. headaches ii. skin diseases iii. asthma iv. bronchitis v. lung and throat cancer.(b) Radioactive wastes thrown into the environment cause: i. giddiness and vomiting ii. infertility iii. cancer iv. defects to unborn babies.(c) Haze caused by dust and smoke: i. reduces visibility ii. increases the risk of road accidents.4. Depletion of food resources(a) Dust and soot on the leaves of plants reduce the rate of photosynthesis, causing less food to be produced by plants.(b) Acid rain causes plants to die because they become unable to absorb water.(c) Acid rain causes aquatic animals such as fish and prawns to be lkilled.5. Destruction of habitats.(a) Acidic gases such as sulphur dioxide and nitrogen oxide which dissolve in water to form acid rain have destroyed large areas of forest and made ponds and rivers unsuitable for plants and animals.(b) As a result the natural habitats are destroyed.6. Extinction of species(a) Destruction of natural habitats has caused many plants and animals to die and several species become extinct.(b) Plants and animals in danger of going extinct include Rafflesia, orang utan, tapir, hornbill and leathery-back turtle.7. Destruction of property(a) Acid rain is corroding buildings and important historic monuments.(b) Smoke and soot have turned many buildings black.8. Global warming(a) The Earth's atmosphere now contains excess carbon dioxide. This is due to fewer forests to absorb the gas and industries releasing a lot of it.(b) This layer of carbon dioxide traps heat from the sun and prevents it from escaping into outer space. As a result the Earth's temperature is rising. The phenomenon is called the green house effect or global warning.(c) Global warning causes: i. icebergs in the poles to melt quickly ii. level of sea water to rise iii. floods in low-lying areas such as some coastal regions9. Thinning of the ozone layer(a) The ozone layer on the atmosphere of the Earth protects us from the harmful rays of the sun.
(b) Harmful ultraviolet rays from the sun can cause:
i. Cataract The eye lens becomes opaque and the patient cannot see. He has to replace the lens with a synthetic one.ii. Skin cancer Constant exposure to harmful ultraviolet rays can causes cancer of the skin. general cancer of the skin, known as melanoma, cannot be cured.iii. Lowering of the body's defence system Harmful ultraviolet rays make the body less able to resist diseases such as tuberculosis and diphtheria.iv. Reducing the yield from plants Plants crops such as paddy give lower yields when exposed to harmful ultraviolet rays.
(c) Air pollutants mainly chlorofluorocarbon (CFC), have made the ozone layer very thin, allowing a lot of harmful ultraviolet rays to reach the Earth.
1. Air pollution must be controlled so that its harmful effects can be reduced. Some ways for controlling air pollution are explained below.
2. Rubbish(a) Do not allow open burning in residential areas.(b) Burning should only be done in approved sites or in incinerators built for the purpose.
3. Motor vehicles(a) Fix catalytic converters to the exhaust pipes of motor vehicles so that harmful. exhaust gases can be converted to harmless substances.(b) Use unleaded petrol in motor vehicles.(c) Ensure that the engines of motor vehicles do not give out excessive exhaust gases and black smoke.
4. Factories(a) Build tall chimneys in factories so that smoke and waste gases are discharged high up in the air and can be easily blown away by wind.(b) Build electric precipitators on the chimneys to attract particles in the waste gases to prevent them from escaping into the air.(c) Treat waste gases in air cleaning systems before releasing them into the air.
5. Agriculture(a) Advise farmers to reduce the use of pesticides.(b) Encourage farmers to use biological control ways to kill pests. For example, suitable owls can be reared in oil palm plantations to catch rats.
6. Chlorofluorocarbon(a) Reduce the use of chlorofluorocarbon and other gases which destroy teh Earth's ozone layer.(b) Use ozone friendly gases such as hydrochlorofluorocarbon (HCFC)
7. Nuclear subtances(a) Store and throw radioactive wastes in the recommended ways.(b) Ban nuclear tests through an international aggrement to be organized by the United Nations.
8. Reforestation(a) replant forest for absorbong carbon dioxide. This reduces global warming.
9. Educating the public(a) Educate members of the public to be aware of the dangers of air pollution and how to control them.(b) This can be done through campaigns in school and talks over radio and television .
10. In order to control air pollution effectively, everyone in the world must co-operate and play his part.
IMPORTANCE OF KEEPING THE CLEAR AIR
1. Smoking is the cause for many deaths through disease such as:(a) bronchitis(b) lung cancer(c) heart diseases(d) emphysema2. Emphysema is a condition in which the air-sacs in the lungs are demaged by cigarrate smoke and cannot function properly. As a result the patient is short of breath. It cannot be cured.3. Cigarette smoke contains over a thousand poisonous chemicals. Some of them may cause cancer of the lungs.4. Nicotine in cigarrate smoke:(a) stimulates the nervous system. (keeps you awake)(b) damages brain tissues(c) hardens blood vessels (makes blood difficult to flow)5. Tar in cigaratte smoke:(a) consists of tiny black particles(b) forms in the lungs as a sticky liquid (blackens the lungs)(c) corrodes the lungs (acidic)(d) contains 17 chemicals which causes cancer in animals.6. Carbon monoxide given out during smoking:(a) is a poisonous gas(b) combines with heamoglobin in the blood, causing the body to lack oxygen.7. A person who is a non-smoker may inhale cigaratte smoke given out by someone smoking. This is called passive smoking.8. Passive smoking can be more harmful to a non-smoker than a smoker.9. Pregnant women who smoke heavily have the risk of having smaller babies, premature birth or still-birth.10. Smokers must be considerate and not smoke in public places or near non-smokers.
1. There will be plenty of health problems without clean air. Patients suffering from breathing difficulties, asthma, bronchitis and skin diseases will increases.2. Haze will reduce visibility and more accidents will occurs.3. Less food will be produced as crops affected by acid rain, soot and dust cannot carry out photosynthesis effectively.4. The air will become warmer with more carbon dioxide in it, causing global warming.5. Warmer air in temperate countries will cause tropical diseases to spread to them.6. The ozone layer will be depleted and more people will suffer from cataract and skin cancer.
1. Run campaigns to discourage cigarette smoking.2. Run campaigns to explain what individuals must do to keep the air clean.3. Ban smoking in public places such as in hospitals, cinema halls, supermarkets and offices.4. Ban open burning of rubbish.5. Prevent forest fires.6. Introduce laws to force factories to treat their waste gases before releasing them into the air.7. Ensure motor vehicles use catalytic converters.8. Fine motor vehicles which give out excessive black smoke.9. Practise reforestation- trees cut down must be replanted.10. Keep a strict watch on the disposal of radioactive wastes.
1. Do not smoke in public places.2. Do not burn rubbish in open air.3. Use less electricity. This will reduce the use of fuels in power stations and so reduce air pollutants.4. Walk or cycle instead og going by cars. This will reduce exhaust gases from motor vehicles.5. Reduce the use of insecticide sprays and hair sprays. This will reduce chlorofluorocarbon (CFC) in the air.6. Ensure your motor vehicles do not give out excessive black smoke.7. Plant trees in your house compounds and in open spaces.
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