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Air Around Us - Composition of Air

Grade 6CBSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Air is a mixture of several gases, water vapour, and dust particles.

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Nitrogen (N2N_2) is the most abundant gas in the atmosphere, making up approximately 78%78\% of the air. It does not support burning.

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Oxygen (O2O_2) makes up about 21%21\% of the air. It is essential for the survival of all living organisms and is required for the process of burning (combustion).

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Carbon dioxide (CO2CO_2) makes up a very small component (about 0.03%0.03\% to 0.04%0.04\%) of the air. Plants use CO2CO_2 for photosynthesis and release O2O_2.

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Water vapour (H2OH_2O) is present in varying amounts depending on the weather and location. Its presence is crucial for the water cycle.

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Dust and smoke are also present in the air. The amount of dust varies from place to place and time to time.

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The balance of oxygen and carbon dioxide in the atmosphere is maintained through photosynthesis by plants and respiration by plants and animals.

📐Formulae

Composition of Air≈78% Nitrogen (N2)+21% Oxygen (O2)+1% Other gases/vapour\text{Composition of Air} \approx 78\% \text{ Nitrogen } (N_2) + 21\% \text{ Oxygen } (O_2) + 1\% \text{ Other gases/vapour}

Photosynthesis: 6CO2+6H2O→SunlightC6H12O6+6O2\text{Photosynthesis: } 6CO_2 + 6H_2O \xrightarrow{\text{Sunlight}} C_6H_{12}O_6 + 6O_2

Respiration: C6H12O6+6O2→6CO2+6H2O+Energy\text{Respiration: } C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{Energy}

💡Examples

Problem 1:

Calculate the approximate volume of Oxygen (O2O_2) present in 500 mL500\text{ mL} of air.

Solution:

Volume of Oxygen = 21% of 500 mL=21100×500=105 mL21\% \text{ of } 500\text{ mL} = \frac{21}{100} \times 500 = 105\text{ mL}.

Explanation:

Since Oxygen (O2O_2) constitutes 21%21\% of the air, we multiply the total volume of air by 0.210.21 to find the volume of oxygen.

Problem 2:

Why does a candle burning in a closed jar extinguish after some time?

Solution:

The candle extinguishes because the Oxygen (O2O_2) inside the jar is consumed during the process of combustion.

Explanation:

Burning requires Oxygen (O2O_2). In a closed jar, the supply of O2O_2 is limited. Once all the O2O_2 is converted into Carbon Dioxide (CO2CO_2) and other byproducts, the flame can no longer be sustained.

Problem 3:

How is the presence of water vapour (H2OH_2O) in air demonstrated?

Solution:

By placing ice-cold water in a glass; droplets of water appear on the outer surface of the glass.

Explanation:

When air comes in contact with a cool surface, the water vapour (H2OH_2O) present in it condenses into liquid water droplets. This proves that air contains moisture.