Air and Atmosphere PDF

Air and CHAPTER Atmosphere 5 LEARNINGOBJECTIVES " Air and its properties " Atmosphere...

Air and CHAPTER Atmosphere 5 LEARNINGOBJECTIVES " Air and its properties " Atmosphere " How is Oxygen replaced in the atmosphere? " Composition of air Rusting of iron " Uses of components of air Airpollution ALR AROUND US Aris a mixture of several gases. We cannot see orsmell air but air is everywhere around us. Even those ntainers and vessels which appear to be empty to us are filled with air. All living things require air. iris inside the human body as well as in the bodies of allother animals and birds. This is because air snecessary for the breathing of all the living things. No living thing can survive without air. Some air spresent even in the water of ponds, lakes, rivers and Keans in the dissolved form. Though we cannot see air but we can feel its presence shen it starts moving (or blowing). Moving air is called wind. Moving air makes the clothes hanging on a dothesline sway. High speed winds can even uproot the Tees and blow off the tin roofs of houses and factories. PROPERTIES OF AIR of air are as follows: Airytransparent, so we can see through it. The important properties Air is colourless, tasteless and odourless gaseous substance. Ajr has mass. ir Occupies space. Air dissolves in water. Air can be compressed.  Let's Do It Aim To demonsttate that au ocCupes spe W.aler does. Materials Requted Aglass bottle, Water, atub ol cHter the Procedure bottle 1 Fill a tub half with Water water Introduce an nverted elass bottle ntothe water. (a) 3 Now. tilt the 4. Record your bottle sl1ghtly. observations. Observation: When the bottle is inverted straight no Air bubbles water enters into it. However. as soon as the bottie Is go out tilted, the air bubbles start escaping through water and Water enters water enters the bottle. the bottle Inference:There is air inside the bottle that occupies (b) space and does not allowwater to enter into the Fig. 5.1 Air occupres space bottle. Skills: Observation, investigation, interpretation ATMOSPHERE becomes less and less. The air at the top of very Our Earth is surrounded by a layer of air (or high mountains is so thin that it does not haye envelope of air)/The envelope of air that surrounds enough oxygen for the people to breathe propert. the Earth is called atmosphere. The atmosphere So, the people who climb high mountains (called (or layer of air) extends up to many kilometres mountaineers) carry cylinders containing oxygen above the surface of Earth. Atmosphere is gas with them, essential for life on Earth. This is because atmosphere provides Oxygen gas for breathing by all the living organisms including us. As we go Think &Answer higher up in the atmosphere, the amount of air Is air a matter? Explain giving reason. Atmosphere COMPOSITION OF AIR Air is a mixture of many gases. The majo component of air is nitrogen gas. Almost four-fifths of air is nitrogen gas. Thesecond About major component of air is oxygen gas. additionto Fig. 5.2 Atmosphere one-fifth of air is oxygen ggas. Inalsocontains nitrogen and oxygen gases, air  mallamounts of carbon dioxide gas, water vapour andsome other gases (such as argonsome Nitrogen odeourless ndhelium,etc.) The air may also contain Nitrogen Isa colourless, lasteless and important tor t particles, The composition of air in terms Sust, gas. Nitrogengas present in air is fpercentage ofits various components can be Iiving thigs. Al the Iiving things need nitrogen writtenasfollows: compounds tor their growth. Theplants use These (omposition of Air nitrogen gasof the airtomake protens. proteins are usedby the plants for their own Nitrogen: /8 per cent growth as well as for the growth of human beings cent and other animals. Oxygen: 21 per Carbon dioxide, water vapour, other gases, Oxygen and dust particles: 1 per cent Oxygen is a colourless, tasteless and odourless gas. Oxygen gas is slightly soluble in water. VTmOxygen gas is essential for breathing actually the When a person breathes in air, jilis in the Oxygen Oxygen present in air which is utilized Nitrogen 20.9% process of respiration. $6, we can also say that 78% Argon gases Oxygen is necessary før breathing. 0.90% around Other gases Under ordinary conditions, we use the air 0.17% us for breathing purposes. But under special Carbon dioxide situations, oxygen gas cylinders are used for 0.03% breathing purposes. For example: Ag. 5.3Composition of air /The patients suffering from diseases like asthma, the etc., have sometimes difficulty in breathing ne composition of air is not always exactly properly in air because only one-fifth part of air me. The composition of air changes slightly is Oxygen. Allthe hospitals have cylinders filled season. For om place to place and season to with oxygen gas for such patients. usually ample, the air over industrial cities dioxide in At high altitude of mountains, the air is very 5ahigher amount of carbon thin.So, the air at high altitudes contains very air in han the air over open spaces. The difficult vapour than little oxygen due to which it becomes Stalareas may have more water the more water tobreathe properly. The mountaineers use and areas. The air also contains breathing amount Oxygen gas contained in cylinders for Our in rainy season. Similarly, the properly under conditions of high altitudes. dust in the air is more in windy places than er areas. When the divers go deep into seawater, thev with then. This carry oxygen gas cylinders dissolved in is because the amount of oxvgen dy of Components of Air water isvery low for the divers tobreathe. air in Will now discuss all the components of Air and Atmosphere 91  Oxygen gas Oxygen gas cylinder Cylinder ,Oxygen gas cylinder Sea diver Patient Mountaineer \Fig. 5.4 Oxygen gas cylinders used for breathing Let's Do It Aim: To demonstrate that air is a mixture of gases. Materials Required: Aglass trough, water, caustic soda. ink, a metallic block, candle, and large gas jar Procedure: 1. Take aglass trough and fill it about one-third with water. 2. Dissolve one teaspoonful of caustic soda in water. 3. Now, add a few drops of ink. 4. Place the metallic block in the water and fix a candle on it. 5. Light the candle. 6. Cover the lighted candle with the large gas jar. -- 7. Record your observations. Inverted gas jar Air Burning candle Nitrogen -- - --- Water rises due to Water. consumption of oxygen -Gas jar Trough stand of air Fig. 5.5 Air is amixture of gases Observation: candle continues to burn tor some time and then The rises up in the bottle when the candle goes of. the flame goes off The coloured water Inference: Thecandle burns as long as oxygen is because oxveen of air is used up in the avallable in the gas jar. The water rises up in the burning process. The carbon dioxide bottle is absorbed by the formed asa result of caustic soda solution. It burning Nitrogen is the major part of air which is notcreates vacUum in the gas jar that causes water to rise up. a used up oy a burning candle as it Therefore, it is stillpresent in the bottle. does not support burning Skills: Observation, Application,Investigation 92 Air and Atmosphere  supports Dxygen burning or combustion process of/(hurning of a substance iS called burning. Air is also blown for burning of wood in ombustion. Air is necessary for the chulha. substance(or burning Whena suubstance Combustion of a burns in air, it substance ). sed tor biowng a Dertorated is presentin air oXYgen which is used actually up in the processof fburning. Thus, whether we the necessaryfor burning or say that air s oxygen is necessary for burming,it means the same thing. fou may have seen that even in (a) Traditional chulha (b) Kerosene stove hulha, kerosene traditional stove, etc., air is made available Fig. 56 Oxygen (air) required for burning or burning. chulha, there are gaps between In he piecesofvwOod so that air remain available for In kerosene stove also air is made available through arrangement of perforated cylinder. Let's DoIt }EL Aim: To demonstrate that air is necessary for burning. Materials Required: Acandle, a matchbox, a gas jar invete Procedure: 1 Take a candle and fix it on aplane surface. Burning Candle 2. Light the candle by using matchstick. candle 3. Now, cover the burning candle by putting an inverted gas jar over it. 4. Record your observations. b (a) Observation: The candle stops burning within ashort Fig. 5.7 Air is necessary for burning time when covered with the gas jar otherwise it Continues to burn. supports candle stops burning because component of air (oxygen) present in the jar, which Inference: The bårning, is used up. Skills: Observations, Interpretation, Investigation by from air and water from soil to make food irbon dioxide the food the process of photosynthesis. So, all Tbondioxide is a colourless and odourless which animals (including human beings) cat is dioxide is air. Without It has a slightly sour taste. Carbon made from carbon dioxide gas of the plants derately soluble in water. Carbon dioxide carbon dioxide in air there would be no nguishes a burning fire. Plants and plants which Iive in or animals on the Earth) The dissolved respiration in water ials consume oxvgen from air for water use the carbon dioxide produce carbon dioxide. for their needs. make nplants need carbon dioxide gas to dioxide d. In sunlight. green plants use carbon Air and Atmosphere 93  Let's Do It EL Aim: To demonstrate that ar contans carbon diO0 tube, lime water Materials Required Atest tube Cork with a hole Rlass Procedure 1. Take some fresh me watet ) a test tube 2 Introduce aglass tube nto the cork Now, fit the cotk 3. Blow ait into the glass tube trom your mouth Iirne water 4. Record vour turns m observations Observation: The Ime water turns milky Fig. 5.8 Ar conane Interence: The carbon dioxde present in the blown air turns the ime wat carbon diorde Skills: Observation, Interpretation, Investigation Water vapour Smoke Air also contains water vapour. We cannot see Smoke is also present in the air. Smoke consists water vapour present in air because it is 'water of fine carbon particles and some gases. Smoke in the form of a gas. When air comes in produced by the burning of fuels (such as wood contact with acool surface (as that of a glass containing coal, kerosene, petrol, and diesel, etc.). Smoke is ice-cold water), the water vapour present in it always harmful. Breathing in air containing smoje condenses to form tiny drops of liquid water on damages our health. We usually see tallchimners the cold surface. Water vapour comes into the in factories. The tall chimneys in factories are air from the evaporation of water present on installed to take the smoke produced in the the Earth (in ponds, lakes, rivers and oceans, factories high up in the air so as to reduce its etc.) and from transpiration. The presence of harmful effects on the ground. water vapour in air is important for the working The burning of fuels such as petrol and diesel of water cycle in nature. This is because it is in the engines of vehicles (such as cars, buses water vapour present in air which rises high and trucks, etc.)also produce smoke containing in the sky along with hot air, gets cooled, condenses to form clouds and then brings rain harmful gases. This smoke is emitted into air on the Earth. through the exhaust pipes connected to the engines of vehicles. Fig. 5.9 Water vapour condenses to form clouds Fig. 5.10 Smoke being emitted by he exhaust pipe of a vehicle 94 Air and Atmosphere  Dust particles at homes,etc. The presence of dust particles in air Dust particles are always present in air. The dust varies from time to time and place to place. Dust particles come into ar from a number of sources. particles are amajor cause of air pollution. Dust For example, traffic on the roads, blowmg of wind, partides present in air may enter our respiratory agricultural particles, volant eruption, dusting system(lungs, etc) and damage our health. Let's Do It EL Aim: To demonstrate the presence of dust particles in the air Materials Required: Black chart paper Procedure: I. Darken a room completely byputting black chart papers on its windows and black curtain on its door. 2. Make a small hole inthe black chart paper fixed on the window which faces the Sun. 3. Record your observations. Dark room Window Srrnall hole Pathof light Floating dust particles Fig. 5.11 Air contains dust particles Observation: Tinydust particles moving in the beam of light in the dark room are clearly visible. Inference: The dust particles are visible in the beam of light. This shows that air contains dust particles. Skills: Observation, Application, Interpretation Inert gases USES OF AIR Inert gases such as helium, neon, argon, krypton and Air is useful to human beings in many ways. Some Xenon are also present in small amounts in air. These of the important uses of air are given below: are non-reactive gases. These gases have various 1. Air isused by living beings for breathing (or Uses. For example, argon and neon are used in respiration). electric bulbs, helium is used in air balloons, xenon and krypton are used in photography. Air and Atmosphere 95  Air is used for burning fuels (ike wood, coal rank and kerosene, etr)whhis used bv us tor Wind coOking tood and other hcating purposes. No fuel can bårn wnthout the ovgen of at. Blades of 3.Compressed air is uNed to fill tvres ot wind pll Pump Various kinds ot vehsles such as bicycles, Pole sCooters, cars, buses, trucks and aeroplanes. The air is also used tor intlating balloons Fig. 5.13 A windnill and footballs. Airhelps inthe 6. Airhelps in the movement of yachts dispersal ot seeds and (sailing boats). parachutes, gliders and pollen of tlowers of aeroplanes. several plants. 7. Air helpsthe birds, bats and insects in 5. Moving air (called flying The birds, bats and insects fly by pushing wind) is used to turn the the air downwards and backwards with their blades of windmills. The Fig. 5.12 Dispersa! of seeds by dir wings. windmills are then used to draw water by running pumps, to run flour 8 Air plays an important role in the water cvcle mills and to generate electricity. The windmill in nature. This is because hot air, being lighter used to run apump todraw water from the rises up and carries the water vapour high un ground is shown in Fig. 5.13. in the sky and helps in bringing rain. Test Your Understanding 1. Which of the following is not correct? a. Air can be compressed b. Air occupies space C. Air does not have mass d. Air is a mixture of gases 2. Air is considered to be: a compound b a mixture C. asolvent d. an element 3. The envelope of air that surrounds the Earth is called a. universe b OZone layer C. atmosphere d. uv layer 4 The two gases which, taken together, make up about 99 per cent of air are: A. Nitrogen B. Carbon dioxide C. Ozone D. Oxvgen a. A and B b. A and C C. B and D d. A and D -bich of the following is not acommon b Nitrogen component of air that we normally breathe in? a. Oxygen C. Carbon monoxide d. All of these 6. Nitrogen is needed by the plants to make: a. fats b carbohydrates C. proteins d. minerals Air and Atmosphere 96 HOW IS OXYGEN AND CARBON In this wav, the plants and animals help in DIOXIDE BALANCED IN NATURE maintaning the balance of oxvgen and corbon The oxygen of air being consumed by animals dioxide gases in air (or atmosphere). This shows (and plants) in respiration, and in the burning the interdependence ot plants and animals in nature. of fuels is constantly being replaced by plants through the process of photosynthesis. This Think & Answer happens as follows:(During the day plants use What would happen if there is no tree on the Earth ? carbon dioxide and water to make food by the process of photosynthesis and produce oxygen gas. Plants also consume some of the oxvgen for RUSTING respiration butthey produce much more oxygen than they consume. The oxygen produced by When an iron object is left in damp air (or water) plants is used by animals (including human for a considerable time, it gets covered with a red beings) to live. This means that animals depend brown flaky substance called rust. This is on plants for getting oxygen gas for breathing. called rusting of iron. The carbon dioxide of air being consumed by During the rusting plants in photosynthesis is constantly being of iron, iron metal put back into air by the respiration of animals combines with the Fig. 5.15 Rusting of iron (and plants), as well as by the burning of fuels Oxygen (of air) in the presence of water (moisture) by human beings. This happens as follows: to form a compound »iron oxide. Rust is iron oxide The animals and plants use oxygen from air for (Fe,0,). Thus, rust and iron are not the same respiration and give out carbon dioxide gas. substance. Rust is different from iron on which it gets deposited. Conditions Necessary for Animals breathe in Rusting Oxygen and breathe Two conditions are necessary for the rusting of Plants take in carbon out carbon dioxide dioxide and give out iron to take place: Oxygen during the presence of oxygen (of air), and daytime ii. presence of water or water vapour (called Fig. 5.14\Balance of oxygen and carbon dioxide in moisture). the nature Iron rustswhen placed in damp air (or moist air), or This carbon dioxide goes back into air. Similarly, when placed in water. Now, damp air (or moist air). the burning of fuels (wood, coal, kerosene, petrol, also contains water vapour. Thus, damp air alone diesel and LPG) by the human beings uses oxygen provides both the things, oxygen and water, required from air and produces carbon dioxide gas. This for the rusting of iron to occur. Again, ordinary carbon dioxide also goes back into air. This means water always has some dissolved oxvgen in it. So, that plants depend on animals for getting carbon ordinary water also supplies both the things, oxygen dioxide gas for photosynthesis. and water, needed for the rusting of iron. Air and Atmosphere 97  Prevention of Rusting Sources and Harmful Effects If air and water are of Air Pollutants prevented contact with iron obeis, thentromOning m usting will ot take Ar pollution producces a large number ot place. Thus, most ot the mcthods ot ctfets on livng and non livng bad preventing cttects are as tollowing things rusting of iron mvolve coatng the ro obietih sOmethng to hep out ar and water. Ironcan he Sulphur protected trom usting dioxide: by painting, ong or Sulphur greasing its surtace. dioxide is Rustingot iron can produced by also be prevented by the burning galvanisation mcthod. of fuels (coal, Fig. 5.17 Ar pollut In this process a thin Fig. 5.16 Painting iron petrol and diesel etc.)in factories, vehicle:e layer (or coating) of zinc articles for preventing metal is deposited on rusting thermalpower plants. iron objects. Sulphur dioxide gas in the polluted air causes respiratory problems. It may even cause permanent lung damage. Sulphur dioxide Test Your Understanding gas in polluted air produces acid rain. This acid rain damages trees, plants, soil, aquatic Fill in the blanks. animals (like fish), statues, buildings and 1. The plants use gas in historical monuments. Sulphur dioxide also photosynthes1s. contributes to the formation of a deadly air 2 and pollutant called smog. are reguired for rusting. Nitrogen oxides: Nitrogen oxides are produced 3. Rust is 4 IS used to turn the by the burning of fuels. Nitrogen oxides attack blades of a windmill. breathing system and lead to lung congestion. 5. Plants use gas during They also attack skin. Just like sulphur dioide. respiration. nitrogen oxides present in polluted air prode acid rain. Nitrogen oxides also contribute oh formation of smog. AIRPOLLUTION Carbon mònoxide: Carbon monoxide is The contamination of air vith harmful gases, produced by the incomnplete combustion otdes Smoke and dust, etc., is called air pollution. The fuels like wood, coal, kerosene, petrolland Carlr substances whose presence in air make it impure in homes, factories and motor vehicles. pollutants. The or contaminated are called air monoxide is a very poisonous gas, IWhen wththe major pollutants which cause air pollution inhaled, carbon monoxide combine carbon are sulphur dioxide, nitrogen oxides, haemoglobin of our blood and reduces Lht th chlorofluorocarbons lhe monoxide, carbon dioxide, OxYgen carrying capacity of fblood. (breathis as dust. and suspended particulate matter (such OXygen causes respiratory Problems smoke and fly ash). problens). It causes suflocation. Air and Atmosphere 98. Carbon dioxide: Carbon dioxide is in excessive amounts by the produced Controlling Air Pollution burning of large We can also contribute in theefforts to control air quantities of fuels such as wood, coal, kerosene, petrol, diesel, etc. in homes, factories and pollution. Some of the steps which can be taken motor vehicles. Though carbon dioxide is a as individuals (or as a group of individuals) to normal constituent of air but excess of carbon control air pollution and improve the quality of air dioxide in air is considered as a pollutant around us are as follows: (because it produces undesirable changes in i. We should not burn dry leaves, papers the environment). Carbon and garbage in the open. Leaves should be dioxide is the main greenhouse gas which traps Sun's heat in the converted into compost by burying in a pit; Earth's atmosphere by producing greenhouse used papers should be sent to paper mills for effect which leads to global recycling; and garbage should be deposited warming. in the garbage dumps established by the Do You Know? Municipal Corporation of the city. Burning coal in a closed room in a hearth ii. We should save electricity. If all of us start (angeethi) is very harmful. The oxygen saving electricity by avoiding its wastage in available in the closed room is used up during homes, schools, shops, offices and factories, burning of the coal. The coal on fire in the the demand for electricitywill decrease. This hearth starts emitting carbon monoxide, a will lead tothe burning of less coal to generate poisonous gas, which is inhaled by the person electricity. And burning of less coal will reduce sleeping inside and this may even cause the air pollution. death of the person sleeping in that room iii. We should grow more trees and also take care of the existing trees inour neighbourhood. Chlorofluorocarbons:Chlorofluorocarbons Trees reduce pollution by absorbing excess are the chemical compounds made of carbon dioxide from the air. Allof us should chlorine, fluorine and carbon elements. participate in Van Mahotsav functions when Chlorofluorocarbons are used in refrigeration, lakhs of trees are planted in July every year. air conditioning and aerosol sprays. iv. We should join Say No to Crackers" Chlorofluorocarbons are industrially useful campaign organised by children of many gases but they also behave as air pollutants schools during Diwali days to reduce the level because of their damaging effect on ozone of air pollution during the festival season. layer (which protects us from harmful UV v. We shoulduse bicycle for covering short radiation from the Sun). distances. This willsave precious fuel like Suspendedparticulate matter: The finely petrol (which we use in cars, scooters and divided solid or liquid particles suspended in air motorcycles) and also reduce air pollution. are called suspended particulate matter. Some vi. If the school is not far off, we shouldgo to of the examples ot suspended particulate matter school on foot or by a bicvcle. Otherwise we are: dust, smoke and fly ash. These particulate should use the school bus or public transport matter produces allergic reactions in human bodyand also causes respiratory diseases. bus for going to school. In nocase should we use a car individually to go to school. If, Air and Atmosphere 99  however, sufficient number of students go to the same school from an area, then a Atmotiere can be tomed for gomg to catpool school Greenhouse Effect and Global Sola Warming Th Raatot warmng up (or ieatng up) of the tarths Earth atmosphereduc to the trapping of Suns eat ravs thv carbon dioxvide gus in the atosphere. is called greenhouse effect. yhe warming (or heating) of the Earth produced b greenhouse etfect is for the important existence of life on the Earth. This is \Eig. 5.18 Greenhouse effeu because it is due to the warming of Earth by the greenhouse effect the Earth has become a habitable Effects of global warming planet having millions of different lifeforms on it. The problem, however, arises when the amount of The rise in temperature of atmosphere will carbon dioxide gas in the atmosphere increases too melt the enormous amount of ice lying on th. much leading to the excessive heating of Earth and poles of the Earth. The huge amount of waler its atmosphere. Due to the rapid burning of fossil produced by the melting of polar ice will raise the level of water in the seas and oeans, and fuels and decrease in forests (plants and trees), the amount of carbon dioxide gas in the atmosphere flood the low-lying areas of the Earth. is increasing steadily. The undue rise in the Global warming can reduce rainfallin some temperature of Earths atmosphere due to excessive areas of the Earth leading to drought. greenhouse effect produced by increasing amounts of greenhouse gases like carbon dioxide, methane, water vapour and nitrous oxide in the atmosphere is called global warming Fig. 5.19 Drought Suspended particulate matter Chlorofluorocarbons Sulphur dioxide Air pollutants Carbon dioxide Nitrogen oxide Carbon monoxide 100 Air and Atmosphere  your Scientist sephPriestley(1733- 1804) was a British clergyman, political theorist, and physical OeNtistHe made SIgnificant advancement in liberal, political and religious thougnts. rememberedfor his is He contributions made in the field of experimental chemistry, chemistry or of gases. He discovered various new gases including oxygen lateridentified as carbon anda gas monoxide. Keywords Atmosphere:The envelope of air that surrounds the Earth Combustion: The process of burning of a substance Transpiration: The loss of water as water vapour from the stomata of leaves Rusting: Formation off a red brown flaky substance on iron objects zinc over it Galvanisation: Process of preventing iron from rusting by depositing a layer of Contamination of air with harmful gases, smoke and dust Air pollution: makes it impure Air pollutants: Substances whose presence in air fluorine and carbon elements chlorofluorocarbons: Compounds made of chlorine, the air matter: The finely divided solid or liguid particles suspended in Suspended particulate warming up of the Earth's atmosphere due to trapping of Sun's heat Greenhouse effect: The the atmosphere rays by carbon dioxide gas in excessive Earth's atmosphere due to the rise in the temperature of Global warming: The undue greenhouse effect Summary several gases. Air is a m1xture of gaseous substance. colourless tasteless and odourless Air is an envelope of air. tarth is Surrounded by proteins. use nitrogen gas of the airto make which is util1zed in the Ihe plants actually the oXVgen present in air breathes in air, it IS When a person process of respiration. substance) ot a substance (or combustion of a for AT IS necessary for the burning and animals consume oxygen from air burning tire Plants Carbon dioxide extinguIshes a carbon dioxIde espiratIon and produce vapour. A also contauns water Ar and Atmosphere 101