Air composition — KCSE Chemistry

KCSE Chemistry · 85 practice questions · 4 syllabus objectives

28 easy28 medium29 hard

What You'll Learn

Key learning outcomes for this topic, aligned to the KNEC KCSE syllabus.

State the approximate composition of air by volume and identify the main components

Describe the industrial separation of air by fractional distillation and the uses of the products

Discuss air pollution: causes, effects and control of common pollutants (CO, SO₂, NOₓ, CFC)

Air composition

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easySHORT ANSWER4 marks

Name two common pollutants found in air and describe one control measure for each. (4 marks)

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Part (a) — 2 marks

Sulphur dioxide (SO₂) (1 mk)

Nitrogen oxides (NOₓ) (1 mk)

Part (b) — 2 marks

Use of scrubbers in industrial emissions to remove SO₂ (1 mk)

Catalytic converters in vehicles to reduce NOₓ emissions (1 mk)

easySHORT ANSWER4 marks

State two major sources of carbon monoxide (CO) in urban areas and explain their effects on human health. (4 marks)

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Part (a) — 2 marks

Motor vehicle exhausts (1 mk)

Burning of fossil fuels (e.g., coal, gas) in industries (1 mk)

Part (b) — 2 marks

Causes headaches and dizziness due to reduced oxygen delivery in the blood (1 mk)

Can lead to unconsciousness or death in high concentrations due to asphyxiation (1 mk)

easySHORT ANSWER4 marks

Explain how the separation of air through fractional distillation is achieved and state one use of argon obtained from this method. (4 marks)

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Part (a) — 3 marks

Air is first cooled to very low temperatures to liquefy it (1 mk)

The liquid air is then slowly warmed in a fractionating column (1 mk)

Different gases are collected at various levels based on their boiling points (1 mk)

Part (b) — 1 mark

Argon is used in welding to provide an inert atmosphere (1 mk)

Define the process of fractional distillation of air and name two gases obtained from this process along with their industrial uses. (4 marks)