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CBSE • Class 6 • Science • Ch 11

Estimated Time: 45 Mins

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Air Around Us

In CBSE Class 6 Science, "Air Around Us" investigates the atmosphere, proving air has mass and takes up space, detailing air composition (78% Nitrogen, 21% Oxygen, 0.04% CO2, water vapour, dust and smoke), explaining respiration and combustion, exploring dissolved air in water and soil, and highlighting the ecological oxygen-carbon dioxide balance.

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💨 Have You Ever Wondered?

Why can you push an inverted "empty" bottle into water, and water refuses to enter until you tilt it and bubbles rush out?

Air is an invisible physical ocean around us! Discover the composition of our atmosphere and the vital ecological cycle that keeps Earth breathing.

Why This Chapter Matters

Before You Begin (Prerequisites)

Air is needed for breathing and burning
Water evaporates into clouds

What You Will Learn (Core Objectives)

Prove air occupies space and has mass.
State volumetric composition: Nitrogen (~78%), Oxygen (~21%), CO2/Argon/Vapour (~1%).
Demonstrate that oxygen supports combustion while nitrogen does not.
Prove presence of dissolved air in water and soil.
Explain the atmospheric Oxygen-CO2 balance maintained by photosynthesis and respiration.

Chapter Roadmap & Progression

1 1. Air Occupies Space & Atmosphere

2 2. Atmospheric Composition

3 3. Respiration & The Oxygen-CO2 Cyc...

Complete Concept Guide (100% Curriculum Coverage)

1. Air Occupies Space & Atmosphere

Air is a transparent mixture of gases. An inverted empty bottle submerged vertically in water will not fill with water until tilted, allowing trapped air to bubble out. The envelope of air surrounding Earth is the Atmosphere, extending hundreds of kilometres high.

2. Atmospheric Composition

Nitrogen (~78%): Major gas; does not support burning; dilutes oxygen so fires do not burn uncontrollably; used by plants via nitrogen fixation.
Oxygen (~21%): Essential for respiration of all living organisms and necessary for combustion (burning).
Carbon Dioxide (~0.04%): Absorbed by green plants during daytime photosynthesis to make food.
Water Vapour: Drives the water cycle, cloud formation, and humidity.
Dust & Smoke: Filtered by mucus and nasal hairs in the human respiratory tract.

3. Respiration & The Oxygen-CO2 Cycle

Air in Water & Soil: Heating water produces tiny bubbles of dissolved air before boiling; dropping dry soil into water produces bubbles as water displaces trapped air. Aquatic life breathes dissolved oxygen via gills; soil organisms breathe trapped soil air.

Ecological Balance: Animals consume oxygen and produce CO2 during respiration. Plants consume CO2 and produce vast amounts of oxygen during daytime photosynthesis, maintaining atmospheric equilibrium.

Key Formulas, Reactions & Definitions

Air Composition Proportions

$$\text{Air} \approx 78\% \text{ N}_2 + 21\% \text{ O}_2 + 0.9\% \text{ Ar} + 0.04\% \text{ CO}_2$$

Dry atmospheric proportions.

Combustion Word Equation

$$\text{Fuel} + \text{Oxygen} \longrightarrow \text{Carbon Dioxide} + \text{Water Vapour} + \text{Heat} + \text{Light}$$

Combustion requires oxygen.

Conceptual Solved Examples & Case Studies

Example 1

Why do earthworms come out of soil during heavy rains?

Step-by-Step Solution:

Earthworms live in burrows and breathe air trapped between soil particles. Heavy rains flood these air spaces with water, forcing earthworms to the surface to breathe.

Example 2

Why does a burning candle extinguish when covered with a glass tumbler?

Step-by-Step Solution:

The candle consumes the limited oxygen inside the tumbler. Once oxygen is exhausted, burning cannot continue and the candle goes out.

Common Misconceptions & Examiner Traps

Common Misconception

Thinking air is weightless.

Scientific Reality & Correction

Air has mass! An inflated football is measurably heavier than a deflated one.

Visual Learning & Conceptual Map

Volumetric Composition of Dry Air

Atmospheric Gas Distribution

78%

Nitrogen (N₂)

21%

Oxygen (O₂)

1%

Others (Ar, CO₂, H₂O)

Chapter Summary & 10 Key Takeaways

Takeaway 1

Air is a mixture of gases: 78% Nitrogen, 21% Oxygen, 0.04% CO2, water vapour, and dust.

Takeaway 2

Oxygen supports respiration and combustion.

Takeaway 3

Water and soil contain dissolved and trapped air.

Takeaway 4

Plants and animals balance oxygen and CO2 through photosynthesis and respiration.

Check Your Understanding (Diagnostic Practice Questions)

Diagnostic questions testing core conceptual clarity. Answers are hidden initially — solve each problem first, then click to reveal the step-by-step verified solution.

Why do mountaineers carry oxygen cylinders on high peaks?

Reveal Answer & Explanation

Answer: At high altitudes, atmospheric pressure drops and air becomes thin, providing insufficient oxygen per breath for human survival.
Air density decreases at high altitude.

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