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Air and Atmosphere - Composition of Air

Grade 6ICSE

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

🔑Concepts

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Air is a mixture of various gases, not a single substance. It occupies space, has mass, and exerts pressure.

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The major component of air is Nitrogen (N2N_2), making up approximately 78%78\% of the total volume. It is relatively inactive and helps in controlling the process of combustion.

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Oxygen (O2O_2) constitutes about 21%21\% of the air. It is essential for the respiration of all living organisms and is a supporter of combustion.

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Carbon dioxide (CO2CO_2) is present in a very small amount, approximately 0.03%0.03\% to 0.04%0.04\%. It is vital for green plants to perform photosynthesis.

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Inert gases like Argon (ArAr) make up about 0.9%0.9\%, while water vapor, dust particles, and smoke make up the remaining small fraction.

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The amount of water vapor in the air is known as humidity. It varies from place to place and time to time, influencing the weather.

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Air is considered a mixture because its components can be separated by physical means (like fractional distillation of liquid air) and it does not have a fixed chemical formula.

📐Formulae

Percentage of Oxygen in Air=Volume of OxygenTotal Volume of Air×100≈21%\text{Percentage of Oxygen in Air} = \frac{\text{Volume of Oxygen}}{\text{Total Volume of Air}} \times 100 \approx 21\%

Photosynthesis: 6CO2+6H2O→Sunlight/ChlorophyllC6H12O6+6O2\text{Photosynthesis: } 6CO_2 + 6H_2O \xrightarrow{\text{Sunlight/Chlorophyll}} 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}

Rusting: 4Fe+3O2+xH2O→2Fe2O3⋅xH2O\text{Rusting: } 4Fe + 3O_2 + xH_2O \rightarrow 2Fe_2O_3 \cdot xH_2O

💡Examples

Problem 1:

During an experiment, a student inverted a glass jar over a burning candle placed in a trough of water. Why does the water level rise inside the jar after the candle goes out?

Solution:

The water level rises to occupy approximately 1/5th1/5^{th} of the jar's volume.

Explanation:

Burning requires Oxygen (O2O_2). As the candle burns, it consumes the O2O_2 present inside the jar. Once the O2O_2 (which is about 21%21\% or roughly 1/5th1/5^{th} of air) is exhausted, the flame goes out. The reduction in air volume creates a partial vacuum, causing the water to rise and fill the space previously occupied by the consumed O2O_2.

Problem 2:

Why is Nitrogen (N2N_2) considered important for life even though humans do not breathe it in for energy?

Solution:

Nitrogen is essential for the synthesis of proteins and DNA.

Explanation:

While humans cannot directly use atmospheric N2N_2, plants convert it into nitrates with the help of bacteria. These nitrates are used to make proteins, which animals and humans consume. Additionally, N2N_2 in the atmosphere dilutes the effect of O2O_2, preventing rapid and uncontrollable fires.

Problem 3:

Calculate the approximate volume of Nitrogen in 500500 liters of air.

Solution:

390390 Liters

Explanation:

Since Nitrogen (N2N_2) accounts for 78%78\% of the air, the volume can be calculated as: 78100×500=0.78×500=390\frac{78}{100} \times 500 = 0.78 \times 500 = 390 liters.