Contents
The concept of equilibrium constants is fundamental in Chemistry Topics as it quantitatively describes the extent of chemical reactions at equilibrium.
How does carbon get into the atmosphere?
Carbon dioxide is a colourless and odourless gas. It has a slightly sour taste. Carbon dioxide is moderately soluble in water. Carbon dioxide gas neither burns nor supports burning. Carbon dioxide extinguishes a burning fire. Plants and animals consume oxygen from air for respiration and produce carbon dioxide. Plant and animal matter burns by consuming oxygen from air and produces mainly carbon dioxide and a few other gases. If some material is burning in a closed room, we feel suffocated. This is due to the accumulation of excess of carbon dioxide (and some carbon monoxide) in the air of the room which is produced by the burning material.
Air contains only about 0.03 per cent of carbon dioxide gas. Though the amount of carbon dioxide in air is comparatively small but it is a very important component of air. The carbon dioxide gas present in air is important to green plants. Green plants need carbon dioxide gas to make food. In sunlight, green plants use carbon dioxide from air and water from soil to make food by the process of photosynthesis. So, all the food which animals (including human beings) eat is made from carbon dioxide gas of the air. Without carbon dioxide in air there would be no plants or animals on the earth. The plants which live in water use the carbon dioxide dissolved in water for their needs.
Water Vapour
Air also contains water vapour. We cannot see ‘water vapour’ present in air because it is ‘water in the form of a gas’. We performed an activity in the previous chapter to show the presence of water vapour in air. When air comes in contact with a cool surface (as that of a glass containing ice-cold water), the water vapour present in it condenses to form tiny drops of liquid water on the cold surface. Water vapour comes into the air from the evaporation of water present on the earth (in ponds, lakes, rivers and oceans, etc.) and from transpiration. The presence of water vapour in air is important for the working of water cycle in nature. This is because it is water vapour present in air which rises high in the sky alongwith hot air, gets cooled, condenses to form clouds and then brings rain on the earth.
Dust Particles
Dust particles are always present in air. The presence of dust particles in air can be shown as follows.
Activity
We darken a room completely by putting black chart papers on its windows and a curtain on its door.
A small hole is made in the black chart paper fixed on that window which faces the sun (see Figure). A thin beam of sunlight enters the darkened room through the small hole made in the window. We can see the tiny dust particles moving in the beam of light in the dark room (see Figure). Actually, the air in a room always contains some dust particles but they are so small that normally they are not visible to us. These tiny dust particles floating in air become visible and can be seen by us only when a thin beam of sunlight falls on them. This activity shows that air contains dust particles.
The dust particles come into air from a number of sources such as blowing of wind, traffic on the roads, dusting at home, earth moving operations, construction activities and agricultural practices. The presence of dust particles in air varies from time to time and place to place. We normally breathe in air (inhale air) through our nose. This is because fine hair and mucus are present inside the nose to prevent dust particles from entering into our respiratory system. We should never breathe in air (or inhale air) through our mouth. This is because if we breathe through our mouth then dust particles present in air may enter our respiratory system (lungs, etc.) and damage our health.
Smoke
Sometimes, smoke is also present in the air. Smoke consists of fine carbon particles and some gases. Smoke is produced by the burning of fuels (such as wood, coal, kerosene, petrol, and diesel, etc.). Smoke is always harmful. Breathing in air containing smoke damages our health. We usually see tall chimneys in factories. The tall chimneys in factories are installed to take the smoke produced in the factory high up in the air so as to reduce its harmful effects on the ground (where people live) (see Figure). The burning of fuels such as petrol and diesel in the engines of vehicles (such as cars, buses and trucks, etc.) also produces smoke containing harmful gases. This smoke is emitted into air through the exhaust pipes connected to the
engines of vehicles (see Figure). The traffic policemen who regulate traffic at crowded city road crossings often wear masks (see Figure). The traffic policemen wear masks to protect themselves from the smoke containing harmful gases which is emitted by the vehicles moving around them.
How Does Oxygen Become Available to Animals and Plants Living in Soil
The animals which live in soil and the plant roots which grow in soil need oxygen to breathe (or respire). They get this oxygen from the air present in spaces between the soil particles. We will now describe a simple activity to show that soil has air in it.
Activity
We take some dry soil in a beaker. Add water to the beaker and stir the soil and water with a glass rod for a while. We will see the bubbles coining out of the soil (see Figure). These bubbles are of the air which was present in spaces between the soil particles.
Actually, when we stir the soil with water, then water enters the spaces between the soil particles and expels the air present there.
This expelled air is seen in the form of bubbles coming out from the soil. So, this activity shows that soil contains air.
We can now say that air is also found in soil. The air is present in the spaces between the soil particles. The animals which live inside the soil get oxygen for breathing (or respiration) from the air present between the soil particles. However, when it rains heavily, all the spaces occupied by air in the soil get filled with water and no air is left in the soil. In such a situation, the animals living inside the soil have to come out of the soil to obtain air for breathing (or respiration). This will become more clear from the following example. The earthworms normally live inside the soil. The earthworms come out of the soil only during heavy rains. This can be explained as follows : During heavy rains, all the spaces in soil which contained air get filled by rainwater leaving no air in the soil for the earthworms to breathe in. Due to this, the earthworms have to come out of the soil to obtain air for breathing (or respiration).
Many animals living in soil dig burrows and holes deep into the soil. These burrows and holes also make spaces available for the air to move into the soil so that it can be used to obtain oxygen by the animals living there. We know that the roots of land plants grow in the soil. And soil has air in it. So, the roots of plants which grow in soil get the oxygen for respiration from the air present between the soil particles. From this discussion we conclude that air in soil is necessary for the animals and plants living in the soil. It is a common observation that a lump of cotton wool shrinks when put in water. This is because I the lump of cotton wool contains a lot of air in the large spaces between its fibres which gets expelled by water resulting in its shrinkage.
How Does Oxygen Become Available to the Animals and Plants Living in Water
The animals (like fish) which live in water are called aquatic animals. The plants which live in water are called aquatic plants. The aquatic animals and plants live in the water of ponds, lakes, rivers and seas (or oceans). The water of ponds, lakes, rivers and seas has some dissolved air in it. So, the animals and plants which live in water use the air dissolved in water for breathing (or respiration). Since air contains oxygen, therefore, we can also say that the animals and plants which live in water use the oxygen dissolved in water for breathing (or respiration). We will now describe a simple activity to show that water contains dissolved air in it.
Activity
Take water in a beaker and keep it on a tripod stand. Heat the water slowly by using a burner. Much before the water begins to boil, tiny bubbles appear on the inside of the beaker (see Figure). These bubbles are of the air which was dissolved in water. Actually, when water is heated, the solubility of air in it decreases due to which the air dissolved in water comes out of water in the form of tiny bubbles.
We can now explain how the living things in water get oxygen. Water has some dissolved oxygen in it. The water animals (like fish) which live in water breathe in oxygen dissolved in water of pond, lake, river or sea. The plants that live in water also use the oxygen which is dissolved in water. Thus, there is oxygen in water too. If there were no oxygen in water, then no living things could survive in water.
How is Oxygen in Air (or Atmosphere) Replaced
We have just studied that a large number of animals and plants are consuming oxygen from air (or atmosphere) for respiration. The oxygen of air is also consumed during the burning of fuels by human beings. Even then all the oxygen of air (or atmosphere) does not get used up. We will now explain how the oxygen in the air is replaced (or refilled).
The oxygen of air being consumed by animals (and plants) in respiration, and in the burning of fuels is constantly being replaced by plants through the process of photosynthesis. This happens as follows : In sunlight, plants use carbon dioxide and water to make food by the process of photosynthesis and produce oxygen gas. Plants also consume some of the oxygen for respiration but they produce much more oxygen than they consume. So, we say that plants produce oxygen gas. Thus, plants constantly refill the oxygen gas into air (or atmosphere) by the process of photosynthesis. The oxygen produced by plants is used by animals (including human beings) to live. This means that animals depend on plants for getting oxygen gas for breathing. Thus, animals (including human beings) cannot live without plants.
We have just discussed that plants keep on using carbon dioxide gas of air for making food by photosynthesis. Even then all the carbon dioxide of air does not get used up. We will now explain how the carbon dioxide in air (or atmosphere) is put back.
The carbon dioxide of air being consumed by plants in photosynthesis is constantly being put back into air by the respiration of animals (and plants), as well as by the burning of fuels by human beings. This happens as follows : The animals and plants use oxygen from air for respiration and give out carbon dioxide gas. This carbon dioxide goes back into air. Similarly, the burning of fuels (wood, coal, kerosene, petrol, diesel and LPG) by the human beings uses oxygen from air and produces carbon dioxide gas.
This carbon dioxide also goes back into air. Thus, the animals (including human beings) constantly put back carbon dioxide gas into air by the process of respiration and burning of fuels. This carbon dioxide is then used by plants for making food by photosynthesis. This means that plants depend on animals for getting carbon dioxide gas for photosynthesis. So, plants cannot live for long periods without animals.
From the above discussion we conclude that respiration by animals and plants, and burning of fuels by human beings uses oxygen from air and puts carbon dioxide into air. On the other hand, photosynthesis by plants uses carbon dioxide from air but puts back oxygen into air. In this way, the plants and animals help in maintaining the balance of oxygen and carbon dioxide gases in air (or atmosphere). This shows the interdependence of plants and animals in nature.
Uses of Air
Air is useful to human beings in many ways. Some of the important uses of air are given on the next page.
1. Air is used by human beings for breathing (or respiration). No human being (or other animal) can survive without the oxygen of air.
2. Air is used for burning fuels (like wood, coal and kerosene, etc.) to make fire. This fire is used by man for cooking food and other heating purposes. No fuel can burn without the oxygen of air. Thus, air is necessary for burning fuels.
3. Compressed air is used to fill tyres of various kinds of vehicles such as bicycles, scooters, cars, buses, trucks and aeroplanes. The air-filled tyres make the transport smooth and easier. The air is also used for inflating balloons and footballs.
4. Air helps in the dispersal of seeds and pollen of flowers of several plants.
5. Blowing air (called wind) is used to turn the blades of wind-mills. The wind-mills are then used to draw water by running pumps, to run flour mills and to generate electricity. The wind-mill used to run a pump to draw water from the ground is shown in Figure .
Let us see how this wind-mill works to draw water from the ground. The blowing air (or wind) rotates the wind-mill blades continuously (see Figure). When the blades rotate, the crank attached to the blades also rotates. When the crank rotates, then its U-bend lifts the pump rod up and down continuously. The rod works the pump which lifts the water from ground.
6. Air helps in the movement of yachts (sailing boats), parachutes, gliders and aeroplanes.
7. Air helps the birds, bats and insects in flying. In fact, birds, bats and insects can fly only due to the presence of air. The birds, bats and insects fly by pushing the air downwards and backwards with their wings.
8. Air plays an important role in the water cycle in nature. This is because hot air, being lighter, rises up and carries the water vapour high up in the sky and helps in bringing rain. Moving air also carries rain clouds from one place to another and helps in bringing rain at all the places.