Teachers TryScience

Composition of Air: Let us Find Out

Mar 12 2016

Source: TTS Haryana Sci...

Summary Information

Keywords:

Air, gases, mixture,oxygen, nitrogen, carbon dioxide, noble gases, water vapour and dust particles

Topic:

Chemistry

Workplace Skills:

Raising Questions

Secondary Research

Discussion

Target Grade (Ages):

Grade 6 (Ages 11-12)

Grade 7 (Ages 12-13)

Grade 8 (Ages 13-14)

Diversity Indicators:

This lesson is most suitable for Indian rural government school students.

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LESSON

Goals and Prerequisites

Goals:

To show that air is a mixture of gases.

Instructional Objective(s)

At the end of the lesson students will be able to -

Demonstrate that air is present in their environment.
Show that air is made up of more than one substance
Identify the presence of the various parts of air.

Instructional Resources

Background:

Air is a mixture of gases. Some of these gases are elements, e.g. Oxygen, nitrogen and others are compounds, e.g. Carbon dioxide. The main gases in the air are nitrogen, 78%. Oxygen, 21%, others, 1%. Among the others are carbon dioxide, about 0.03%, noble gases, about 0.9% and varying amounts of water vapour depending on the weather.

Materials:

Glass jars, candles
Chemicals for testing-lime water, anhydrous copper sulphate.

Procedure:

The gases making up air can be separated by physical means. When a lighted candle is allowed to burn in a specified amount of air, part of the air is used up during the burning. The part of air which is used up during burning is oxygen. The other part which does not support burning is largely nitrogen. The test therefore for oxygen is to burn a substance in it. A glowing splint for instance is rekindled when plunged into a jar of oxygen. Carbon dioxide when bubbled into clear lime water makes it turn milky. The presence of water vapour in the air is shown by allowing white anhydrous copper sulphate to be exposed to damp air. After some time, the white substance becomes blue due to the water vapour in the air. It is therefore possible to demonstrate the presence of the named constituent of air.

The uses of the various parts of air can be summarised:

Oxygen supports burning
Nitrogen useful in the manufacture of fertilisers.
Carbon dioxide is used by plants to manufacture their food
Noble gases used in advertising lamps

RESOURCES

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STANDARDS/CURRICULUM

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