Chapter 5: Air and Atmosphere PDF

# Chapter 5: Air and Atmosphere ## Learning Objectives * Air and its properties * Atmosphere * Composition of air * Uses of components of air * How is oxygen replaced in the atmosphere? * Rusting of iron * Air pollution ## Air Around Us Air is a mixture of several gases. We cannot see or smell a...

# Chapter 5: Air and Atmosphere ## Learning Objectives * Air and its properties * Atmosphere * Composition of air * Uses of components of air * How is oxygen replaced in the atmosphere? * Rusting of iron * Air pollution ## Air Around Us Air is a mixture of several gases. We cannot see or smell air but air is everywhere around us. Even those containers and vessels which appear to be empty to us are filled with air. All living things require air. Air is inside the human body as well as in the bodies of all other animals and birds. This is because air is necessary for the breathing of all the living things. No living thing can survive without air. Some air is present even in the water of ponds, lakes, rivers and oceans in the dissolved form. Though we cannot see air but we can feel its presence when it starts moving (or blowing). Moving air is called wind. Moving air makes the clothes hanging on a clothesline sway. High speed winds can even uproot the trees and blow off the tin roofs of houses and factories. ## Properties of Air Air is transparent, so we can see through it. The important properties of air are as follows: 1. Air is colourless, tasteless and odourless gaseous substance. 2. Air has mass. 3. Air occupies space. 4. Air dissolves in water. 5. Air can be compressed. ## Let's Do It **Aim:** To demonstrate that air occupies space. **Materials Required:** A glass bottle, water, a tub **Procedure:** 1. Fill a tub half with water. 2. Introduce an inverted glass bottle into the water. 3. Now, tilt the bottle slightly. 4. Record your observations. **Observation:** When the bottle is inverted straight no water enters into it. However, as soon as the bottle is tilted, the air bubbles start escaping through water and water enters the bottle. **Inference:** There is air inside the bottle that occupies space and does not allow water to enter into the bottle. **Skills:** Observation, investigation, interpretation ## Atmosphere Our Earth is surrounded by a layer of air (or envelope of air). The envelope of air that surrounds the Earth is called atmosphere. The atmosphere (or layer of air) extends up to many kilometers above the surface of Earth. Atmosphere is essential for life on Earth. This is because atmosphere provides oxygen gas for breathing by all the living organisms including us. As we go higher up in the atmosphere, the amount of air becomes less and less. The air at the top of very high mountains is so thin that it does not have enough oxygen for the people to breathe properly. So, the people who climb high mountains (called mountaineers) carry cylinders containing oxygen gas with them. **Think & Answer?** Is air a matter? Explain giving reason. ## Composition of Air Air is a mixture of many gases. The major component of air is nitrogen gas. Almost four-fifths of air is nitrogen gas. The second major component of air is oxygen gas. About one-fifth of air is oxygen gas. In addition to nitrogen and oxygen gases, air also contains small amounts of carbon dioxide gas, water vapour and some other gases (such as argon and helium, etc.) The air may also contain some dust particles. The composition of air in terms of percentage of its various components can be written as follows: ### Composition of Air * Nitrogen: 78 per cent * Oxygen: 21 per cent * Carbon dioxide, water vapour, other gases, and dust particles: 1 per cent The composition of air is not always exactly the same. The composition of air changes slightly from place to place and season to season. For example, the air over industrial cities usually has a higher amount of carbon dioxide in it than the air over open spaces. The air in coastal areas may have more water vapour than inland areas. The air also contains more water vapour in rainy season. Similarly, the amount of dust in the air is more in windy places than other areas. ## Study of Components of Air We will now discuss all the components of air in detail. **Air Composition Diagram:** The diagram shows a pie chart with the following breakdown of the components of air: * Nitrogen: 78% * Oxygen: 20.9% * Argon gases: 0.90% * Other gases: 0.17% * Carbon dioxide: 0.03%