ILC Chemistry Ordinary Level Option 1B - Atmospheric Chemistry Complete

Curriculum: Irish Leaving Certificate (ILC)

Level: Ordinary Level (OL)

Subject: Chemistry

Optional Topic: Option 1B

Title: Atmospheric Chemistry

Prepared By: ExamsLogic Academic Team

1. Learning Objectives

Describe oxygen, nitrogen and carbon dioxide in the atmosphere.
Explain industrial separation of air by liquefaction and fractional distillation.
Describe the nitrogen cycle and nitrogen fixation.
Explain formation and effects of carbon dioxide, carbon monoxide and acid rain gases.
Describe atmospheric pollution and waste-gas scrubbing.
Explain the ozone layer and how CFCs damage it.

2. Oxygen

Oxygen is an essential gas in the atmosphere. It supports combustion and respiration.

Air can be liquefied and separated by fractional distillation to obtain oxygen and nitrogen.

Topic	Key point
Industrial preparation	Air is liquefied, then fractional distillation separates gases by boiling point.
Uses of oxygen	Medical oxygen, steelmaking, welding and combustion support.
Liquid nitrogen use	Freezing, preservation and cooling applications.

3. Nitrogen

Nitrogen makes up most of the air. It is relatively unreactive because of the strong triple bond in N₂.

N₂ contains a strong triple bond, so nitrogen is quite unreactive.

Subtopic	Key idea
Abundance	Nitrogen is the largest component of air.
Inertness	Its strong bond makes it less reactive at ordinary conditions.
Fixation	Lightning, bacteria and industry convert nitrogen into useful compounds.
Uses	Ammonia production, inert atmosphere, food packaging

Nitrogen Cycle

Stage	Meaning
Nitrogen fixation	Atmospheric nitrogen is converted into compounds plants can use.
Nitrification	Bacteria convert ammonium compounds to nitrates.
Assimilation	Plants take in nitrates and build proteins.
Decay and ammonification	Dead organisms and waste return nitrogen compounds to the soil.
Denitrification	Bacteria convert nitrates back into nitrogen gas.

4. Carbon Dioxide and Carbon Monoxide

Gas	Formation	Importance / risk
Carbon dioxide, CO₂	Complete combustion, respiration, fermentation	Used in photosynthesis; greenhouse gas
Carbon monoxide, CO	Incomplete combustion	Highly toxic because it reduces oxygen transport in blood

Complete combustion → CO₂ + H₂O | Incomplete combustion → CO may form

Related atmospheric ideas

CO₂ can be present free in air and dissolved in water.
Fermentation can produce carbon dioxide.
The carbon cycle moves carbon between air, living things, water and fuels.
Rising greenhouse gases contribute to the greenhouse effect.

5. Atmospheric Pollution

Main atmospheric pollutants in this option are sulfur oxides and nitrogen oxides.

Pollutant	Main source	Effect
SO₂ / sulfur oxides	Burning sulfur-containing fuels	Acid rain, respiratory irritation
NOₓ / nitrogen oxides	High-temperature combustion in engines and furnaces	Acid rain, smog, respiratory irritation

Acid rain is linked mainly to oxides of sulfur and nitrogen.

Scrubbing waste gases

Industrial waste gases can be treated by passing them through alkaline substances such as limestone or bases to remove acidic gases.

Example: Limestone scrubbing helps remove sulfur dioxide from flue gases.

6. The Ozone Layer

The ozone layer in the stratosphere absorbs harmful ultraviolet radiation.

Topic	Key point
Ozone formation	UV light helps convert oxygen into ozone in the upper atmosphere.
Importance	Ozone protects living things from harmful UV radiation.
CFCs / HCFCs	These substances can release chlorine-containing radicals that destroy ozone.
Environmental effect	Ozone depletion allows more UV radiation to reach Earth.

Examiner Trap: Ground-level ozone pollution and the high-altitude ozone layer are not the same thing.

7. Quick Revision Table

Keyword	Meaning
Liquefaction of air	Cooling and compressing air until it becomes liquid
Nitrogen fixation	Changing N₂ into usable nitrogen compounds
Greenhouse effect	Warming due to heat-trapping gases such as CO₂
Acid rain	Rain made more acidic by sulfur and nitrogen oxides
Ozone layer	Protective region absorbing UV radiation
CFC	Compound that can damage the ozone layer

8. Exam Practice Questions

Q1. How is oxygen obtained from air on an industrial scale? [3]

Q2. Why is nitrogen relatively unreactive? [2]

Q3. Outline the nitrogen cycle. [5]

Q4. Distinguish between carbon dioxide and carbon monoxide. [4]

Q5. Name two pollutants that contribute to acid rain. [2]

Q6. Explain why the ozone layer is important. [2]

Q7. State how CFCs damage the ozone layer. [3]

PREMIUM REVISION NOTES