Air
Air is the invisible mixture of gases that surrounds Earth. Air is present all around us. We cannot see it. But we can feel it.
Air contains important substances, such as oxygen and nitrogen, that most species need to survive.
Properties of Air
★ Air is a mixture of many gases, water vapours and dust particles.
★ Air exerts pressure in all directions.
★ Air has mass and weight.
★ Air occupies space.
★ Air supports to burning.
Wind
Moving air is called wind.
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Composition of Air
Air is a mixture of many gases, water vapour, dust particles and smoke.
Nitrogen gas is in largest amount 78%, oxygen is second largest amounted gas 21% in the atmosphere. In 1 per cent carbon dioxide and other gases like argon, helium, neon.
1. Nitrogen: Nitrogen is a gas. Nitrogen gas is present in largest amount in the atmosphere. It is 78 per cent in atmosphere.
★ All living things need nitrogen but they cannot take it directly from the air.
★ Plants get their nitrogen from the soil.
★ Animals get it from plants and flesh of other animals.
★ Nitrogen is also used to make fertilisers, ★ These fertilisers are added to the soil which helps in the growth of plants.
Fertilisers
The chemicals used to increase the fertility of soil is called fertilizer.
Oxygen: It is a gas. oxygen is the most important and second largest amounted gas of atmosphere. It is 21 per cent in atmosphere.
★ All living things need oxygen for breathing.
★ Oxygen in the air is needed for burning.
Q. What is breathing?
Ans. All living things breathe in air to get oxygen. When we breathe, we take in air rich in oxygen. This is called inhaled air. The air we breathe out is called exhaled air.
Q. Work of Breathing?
And. When we breathe in air, the oxygen from the air is absorbed by the blood and taken to different parts of the body and carbon dioxide is given out.
Carbon dioxide: Carbon dioxide is a gas. It is present in very less amount 0.03 per cent in the atmosphere.
Photosynthesis: The process of preparing food by the green plants is called photosynthesis. The to prepare food. During this process, the green plants used carbon dioxide and oxygen is given out.
★ Photosynthesis keeps the percentage of oxygen in the atmosphere, constant.
Other Things present in the Air:
Air also contains water vapour, dust particles and other gases such as argon, helium, neon, etc. (0.97 per cent)
★ Air also contains water vapour. Water from water bodies evaporates to form water vapour.
Water vapour: The gaseous form of water present in atmosphere is called Water vapours. It is due to the evaporation of water bodies like rivers, lakes and seas evaporates and forms water vapour.
Humidity
The amount of water vapour present in the air is called humidity. High humidity makes us feel uncomfortable as our sweat does not evaporate easily.
Places near the sea-coast are generally very humid.
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Atmosphere
Our earth is surrounded by a thick layer of air called atmosphere.
★ Atmosphere extends upto less height of about 800 km
★ The atmosphere is held by Earth's gravity.
Barometer
The instrument used to measure air pressure is called a barometer.
Work of Atmosphere
★ The atmosphere protects Earth from the immense heat and light of the Sun.
★ It prevents the air from becoming too hot during the day and too cold at night.
★ It also stops meteors from hitting our Earth.
★ It gives the right amount of sunlight to green plants so that they can make their food.
Q. Why people have to carry oxygen tanks under water and high on the mountains?
Ans. Even under water and high on the mountains, there is less air, that is why people have to carry oxygen tanks for breathing.
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Layers of Atmosphere
The atmosphere is made of four layers:
Troposphere: The heaviest and the lowermost layer of the atmosphere is called the troposphere.
★ Water vapour is present in this layer. It is in this layer that clouds form and bring rain and snow.
★ Weather changes take place in this layer.
Stratosphere: The layer that lies above the troposphere is called the stratosphere.
★ Ozone is present in this layer of the atmosphere. It protects us from the Sun's harmful ultraviolet rays.
★ Ultraviolet rays can cause skin cancer. Aircrafts usually fly in this layer.
Ionosphere: The third layer lies above the stratosphere is known as the ionosphere.
★ Radio and television signals are beamed into this layer and from here they are bounced back to the earth.
Exosphere: The last and the outermost layer is exosphere.
★ Here the air is very very thin. Beyond the exosphere, lies the space.
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Uses of Air Pressure
Q. Air pressure is used while drinking a cold drink or juice with the help of a straw. How?
Ans. The pressure of air on the surface of cold drink is equal to the pressure of air inside the straw.
When we suck the air from one end of the straw into our mouth, the amount of air in the straw decreases. The pressure of air on the surface of cold drink increase. This pushes the cold drink into the straw which reaches to our mouth.
★ Air pressure is used for filling ink in a fountain pen.
★ Air pressure is used to fill a doctor's syringe.
★ A siphon is a twice bent tube through which we draw liquid from containers. It also makes use of the air pressure.
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Pollution
The presence of unwanted and harmful materials or substances in the ------- is called ------ pollution.
Air Pollution
The presence of unwanted and harmful materials or substances in the air is called air pollution. These harmful substances are called pollutants
Sources of air pollution: may be both natural, or man due to human activities.
Natural Causes of Air Pollution : Air pollutants like dust and smoke may get mixed into air.
Man made Causes of Air Pollution : Air pollutants like burning of fuels, running vehicles
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Human activities which pollute air
★ Burning of wood, coal, kerosene, etc. gives out carbon dioxide and other toxic fumes.
★ Factories and mills give out smoke containing carbon dioxide and other harmful gases.
★ Vehicles like cars, buses, trucks, etc. also emit oxides of carbon, nitrogen and lead.
All these harmful gases and smoke make the air dirty or polluted. The presence of unwanted and harmful things in air is causing air pollution.
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Effects of Air Pollution
Air pollution harms both human health and the environment.
1. Air pollution causes many diseases to all living beings like asthma, bronchitis, lung cancer and other respiratory disorders.
2. It also leads to causes of irritation of eyes, nose and throat.
3. It damages the protective ozone layer. It protects us from harmful rays of the sun.
4. It kills plants and trees by damaging their leaves.
5. It may cause haze due to which visibility may be reduced.
6. It increases amount of carbon dioxide in the air. Increasing of carbon dioxide level in the air leads to globe warming. It is a threat to all living beings.
★ Deforestation
Cutting down of trees on a large scale is called deforestation.
Acid Rain
Pollutant gases like sulphur dioxide and nitrogen dioxide get mixed with rain water, form acids and fall on the earth. This is called acid rain.
Acid rain damages buildings, monuments, iron structures such as bridges, pillars, etc., leaves of trees and contaminate lakes, rivers, ponds, etc.
The white colour of the Taj Mahal located in Agra is turning yellowish due to air pollution.
The industries around the Taj Mahal have been ordered to use cleaner fuels like CNG by the Supreme Court of India.
Control of Air Pollution
★ We should plant more trees as they remove carbon dioxide from the air and release oxygen into the atmosphere.
★ Factories and mills should be locate away from residential areas.
★ Smoke from the factories should be filtered to make it less harmful.
★ Automobiles or vehicles should be checked regularly so that they do not release harmful gases.
★ Vehicles must be fitted with non-polluting fuels such as CNG.
★ More and more plants should be grown because they remove carbon dioxide from the air and release oxygen into it.
Water
SPM = Suspended Particulate Matter
CNG = Compressed Natural Gas
Renewable
Which can be used again and again
it is our duty to prevent and check pollution.
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Water
Water is a colourless, odourless and tasteless liquid. Water carries nutrients to different parts of our body and also helps to remove wastes from it.
We get water from rain, clouds, seas and even inside the earth.
Water covers about 71 per cent of Earth's surface. Almost 70 per cent of our body weight is because of water.
Q. Why the water is called universal solvent?
Ans. It is called a universal solvent as most substances dissolve in it.
Q. Why did the water is not found in pure state?
Ans. Water is never found in its pure form. For example, rainwater before reaching the earth gets mixed with dust particles and other substances present in the air.
Impurities in Water
Water present in wells, rivers and lakes is impure. There are two types of the impurities:
1. soluble impurities and 2. insoluble impurities ★ Disease causing impurities are also present in it.
1. Soluble impurities: The impurities which get dissolved in water is called Soluble impurities.
2. Insoluble impurities: The impurities which do not dissolved in water and some time can be seen floating on water is called Insoluble impurities.
Insoluble impurities of water can be removed by the following methods:
1. Sedimentation
2. Decantation
3. Filtration
1. Sedimentation
This process of settling down of heavy insoluble impurities at the bottom is called sedimentation.
The heavy particles which settle down at the bottom, forming a separate layer in the water. This separate layer of the heaviest impurities is called sediment.
2. Decantation
After sedimension the water from the top can be poured into another beaker. This pouring of water, leaving the sediment behind is called decantation.
3. Filtration
Insoluble impurities can also be removed by the help of the filter so that this process is called filtration. Solid particles will be left behind on the filter paper.
The filter water that collects in the beaker is called filtrate.
How to remove soluble impurities?
The substances dissolve into any liquid (water) is called solute. The liquid (water) in which solute is dissolved is called solvent and this obtained mixture is called solution.
The substances that dissolve in water are called soluble substances. The substances that do not dissolve in water are called insoluble substances.
Name any three substances that are soluble in water.
Sweet, salt, sugar
Soluble impurities can be removed by the following methods:
1. Evaporation
2. Distillation
Evaporation
The process of changing of water or any other liquid into vapour on heating is called evaporation.
Chlorination
The water is disinfected with a small amount of chlorine gas. This process is called chlorination.
Water for drinking and cooking can be purified by the following methods:
* Water can be boiled for 10-15 minutes to kill the germs and then can be stored in a clean container.
* Use a water filter to store drinking water. The filter should be cleaned regularly as a dirty filter can give rise to disease causing germs.
* Potassium permanganate crystals can be added in water to kill the germs present in water.
* A small amount of chlorine can be added in water to kill the germs. This process is called chlorination.
Exercise
A. Tick (✔) the correct option.
1. Which gas is used to produce a coloured glow in glass tubes?
a) oxygen
b) carbon dioxide
c) ozone
d) argon
2. Which method can be used to get salt from salt water solution?
a) distillation
b) evaporation
c) chlorination
d) decantation
3. Which of the following properties is not of air?
a) Air has weight.
b) Air exerts pressure.
c) Air occupies space.
d) Air is universal solvent.
4. This can be used to kill the germs present in impure water.
a) salt
b) sugar
c) potassium permanganate
d) carbon dioxide
5. This water is used in car batteries, science experiments and medicines.
a) distilled water
b) chlorinated water
c) filtered water
d) sedimented water
6. This gas cannot be taken directly from the air by the living beings.
a) oxygen
b) nitrogen
c) carbon dioxide
d) both (b) and (c)
Ans. 1. d) argon, 2. b) evaporation 3. d) Air is universal solvent., 4. c) potassium permanganate 5. a) distilled water 6. d) both (b) and (c)
B. Fill in the blanks.
1. The blanket of ............... around Earth is called atmosphere.
2. The living things need ............... gas to breathe.
3 ........... is the heaviest layer of the atmosphere.
4. .................. impurities can be removed by evaporation.
5. Chlorine gas is used to kill ............... present in water.
Ans. 1. Atmosphere, 2. Oxygen, 3. Troposphere, 4. Soluble, 5. germs
C. True or false.
1. Plants use carbon dioxide for photosynthesis.
2. Water is sweet in taste.
3. Consumption of polluted water can cause dysentery.
4. Ultraviolet rays can cause skin cancer.
5. All impurities are soluble in water.
6. Air does not support burning.
Ans. 1. True, 2. False, 3. True, 4. True, 5. False, 6. False
D. Answer these questions in one or two sentences.
1. Name the four layers of the atmosphere.
Ans. Troposphere, stratosphere, ionosphere and exosphere are four layers of Earth's atmosphere.
2. With the help of a diagram, write the composition of air. Which gas is needed by all living organisms for breathing?
Ans.
Composition of Air
Air is a mixture of many gases, water vapour, dust particles and smoke.
Nitrogen gas is in largest amount 78%, oxygen is second largest amounted gas 21% in the atmosphere. In 1 per cent carbon dioxide and other gases like argon, helium, neon.
3. List three uses of air pressure.
Ans. ★ Air pressure is used for filling ink in a fountain pen.
★ Air pressure is used to fill a doctor's syringe.
★ A siphon is a twice bent tube through which we draw liquid from containers. It also makes use of the air pressure.
4. Name the types of impurities present in water.
Ans. The impurities present in water are either soluble impurities or insoluble impurities. This water also carries disease causing germs.
5. Define the terms (i) Evaporation (ii) Chlorination.
Ans. Evaporation
The process of changing of water or any other liquid into vapour on heating is called evaporation.
Chlorination
This process in which a small amount of chlorine gas is used to disinfected the water is called chlorination.
6. Why should drinking water be purified?
Ans.
E. Answer these questions in detail.
1. Explain with the help of an activity that air exerts pressure in the upward direction.
Ans.
Take a glass and fill it with water right up to the brim. Slide a stiff card on the top of the glass taking care that no air be trapped between the water and the card. Press the card firmly with your hand and turn the glass upside down. Now remove your hand. Observe what happens.
The card does not fall and the water remains in the glass. What does this prove? This shows that air exerts pressure in the upward direction.
2. What is air pollution? How does air get polluted? What can we do to control air pollution?
3. How can you remove insoluble impurities from water?
4. Explain the process of distillation with the help of a well-labelled diagram.
5. How can water be purified before supplying it to towns and cities?
6. Name the two processes that take place during distillation and indicate the conversion of one state of matter into another.
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