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Air, Water, and Weather - Properties and composition of air

Grade 3ICSE

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

🔑Concepts

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Air is a mixture of various gases, mainly Nitrogen (N2N_2), Oxygen (O2O_2), and Carbon dioxide (CO2CO_2).

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Air occupies space: This can be observed when we blow air into a balloon and it expands.

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Air has weight: A balloon filled with air is heavier than an empty balloon.

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Composition of Air: It consists of approximately 78%78\% Nitrogen, 21%21\% Oxygen, and 1%1\% other gases including Carbon dioxide (CO2CO_2) and water vapor.

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Oxygen (O2O_2) is essential for breathing and for burning (combustion).

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Nitrogen (N2N_2) is the most abundant gas in the atmosphere, making up about 78100\frac{78}{100} of the air.

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Air exerts pressure in all directions, which helps in activities like drinking through a straw.

📐Formulae

78% Nitrogen (N2)78\% \text{ Nitrogen } (N_2)

21% Oxygen (O2)21\% \text{ Oxygen } (O_2)

1% Other gases (including CO2 and water vapor)1\% \text{ Other gases (including } CO_2 \text{ and water vapor)}

💡Examples

Problem 1:

Which gas makes up the largest part of the air we breathe, and what is its percentage?

Solution:

Nitrogen (N2N_2) at 78%78\%.

Explanation:

Nitrogen is the most plentiful gas in the Earth's atmosphere, occupying nearly 78%78\% of the total volume.

Problem 2:

If you cover a burning candle with a glass jar, the flame goes out after some time. Which gas was used up?

Solution:

Oxygen (O2O_2).

Explanation:

Burning requires Oxygen (O2O_2). Once the limited amount of O2O_2 inside the jar is consumed by the flame, the fire can no longer burn and the candle goes out.

Problem 3:

How can you prove that air occupies space using a glass and a bucket of water?

Solution:

By pushing an inverted glass straight down into the water.

Explanation:

When an empty glass is pushed vertically into water, the water does not enter the glass because the air trapped inside occupies the space. If the glass is tilted, air bubbles (made of O2O_2, N2N_2, etc.) escape, and water rushes in to take that space.