Air Around Us Class 6 NCERT — Concepts, Experiments, and Solutions

What is Air and Is It Everywhere?

Air is a transparent, odorless, and tasteless mixture of gases that surrounds the Earth. This thick blanket of air extending up to many kilometers above the Earth's surface is called the atmosphere. As we climb higher up in the atmosphere, the air becomes thinner and contains less oxygen. This is why mountaineers carry oxygen cylinders when climbing high peaks.

Air is not a single substance but a mixture of several gases. It occupies space, has weight, and exerts pressure on everything around it. Since it is transparent, light can pass through it, allowing us to see clearly. Without air, life on Earth would be impossible because all living organisms require it to breathe and perform vital biological processes.

Experiments to Prove Air is Present in Water and Soil

1. Step 1: Proving Air is Dissolved in Water — Take some water in a glass beaker and heat it slowly on a tripod stand. Look closely at the inner surface of the vessel before the water begins to boil. You will see tiny bubbles adhering to the sides. These bubbles come from the air dissolved in the water escaping as heat is applied.
2. Step 2: Proving Air is Present in Soil — Take a dry lump of soil or clay in a beaker. Slowly pour water over it. You will observe air bubbles bubbling out of the soil. This happens because water displaces the air trapped in the spaces between the soil particles, forcing it out as bubbles.

Major Components of Air

• Nitrogen: Makes up about 78% (or 4/5th) of the atmosphere. It does not support burning and is vital for plant growth.
• Oxygen: Constitutes about 21% of the air. It is absolutely essential for respiration in living organisms and is required for combustion (burning).
• Carbon Dioxide: Makes up a tiny fraction (about 0.03%). Plants consume it to prepare food during photosynthesis, while animals release it during respiration.
• Water Vapour: Its presence varies depending on the weather. When air hits a cold surface, this vapour condenses into water droplets, playing a major role in the water cycle.
• Dust and Smoke: Created by burning fuels and natural dust. We can easily see dust particles floating when a beam of sunlight enters a dark room.

Common Exam Confusions & Tips

1. Mixture vs. Compound: A common mistake is calling air a chemical compound. Always remember that air is a mixture of gases, and its composition can vary slightly depending on your location (e.g., more humidity/water vapour near coastal areas).
2. Burning Support: Oxygen supports burning, but it does not burn itself. Nitrogen does not support burning at all.
3. Respiration vs. Photosynthesis: Remember that plants perform respiration all the time (breathing in oxygen, releasing carbon dioxide), but they perform photosynthesis (consuming carbon dioxide, releasing oxygen) only during the day in the presence of sunlight.

Practice Questions with Solutions

• Q: Which component of air is essential for respiration? A: Step 1: Identify the main gases present in the air: Nitrogen, Oxygen, Carbon Dioxide, and others. Step 2: Recall that respiration is the process of breaking down food to release energy, which requires oxygen. Final answer: Oxygen is the component of air that is essential for respiration.
• Q: How will you prove that air supports burning? A: Step 1: Fix two small lighted candles on a flat table. Step 2: Cover one candle with an inverted glass tumbler, leaving the other candle completely open to the air. Step 3: Observe both candles. The covered candle will flicker and extinguish after a few seconds because the limited oxygen inside the glass is completely used up. The uncovered candle continues to burn. Final answer: This experiment proves that oxygen, which is a component of air, is necessary for burning.
• Q: Why does a lump of cotton wool shrink in water? A: Step 1: Realize that a dry lump of cotton wool contains a large volume of air trapped in the tiny empty spaces between its fibers. Step 2: When dipped in water, the water enters these empty spaces and replaces the trapped air. Step 3: As the air escapes and the water pulls the cotton fibers tightly together, the cotton shrinks. Final answer: The lump of cotton wool shrinks in water because the trapped air inside its spaces is replaced by water.
• Q: How do plants and animals help each other in the exchange of gases in the atmosphere? A: Step 1: Animals breathe in oxygen from the air and release carbon dioxide during respiration. Step 2: Green plants utilize this carbon dioxide to prepare their food through photosynthesis during the day. Step 3: Plants release oxygen back into the atmosphere as a byproduct of photosynthesis. Final answer: Through this interdependent cycle of respiration and photosynthesis, plants and animals maintain the balance of oxygen and carbon dioxide in nature.

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