Skip to content
Dabour HubLEARN · PRACTICE · EXPLORESign inStudent

2.3Inorganic Chemistry

Gases in the Atmosphere — Edexcel Linear - OL (Chemistry) Revision Notes & Topical Questions

5 min read 8 parts Lesson 10 of 23 Unit quiz

📚 Edexcel Linear - OL (Chemistry) Hub / Topical Revision
🩺
100% Curriculum Specification Match Lesson Doctor Verified
The only platform with 100% curriculum specification match and verified interactive question banks.
0%read
Lesson summary

Gases in the Atmosphere — EDEXCEL LINEAR – OL (CHEMISTRY) notes: Describe the composition of dry air, how oxygen is measured, the sources of atmospheric pollutants and the causes and effects of climate change.Dry air is a mixture, so its gases keep their own properties and are no…

  • Carbon monoxide
  • Sulfur dioxide
  • Oxides of nitrogen
  • Carbon particles (soot)
  • greenhouse gases
  • Worked example 1

Part 1 of 6Composition of clean dry air

Dry air is a mixture, so its gases keep their own properties and are not chemically combined. By volume it is approximately:

GasApproximate percentage
Nitrogen78%
Oxygen21%
Argon (noble gas)0.9%
Carbon dioxideabout 0.04%
Other gases (neon, helium, water vapour)trace

Nitrogen is unreactive, so it remains in the air in large amounts. Argon is a noble gas used in filament lamps and welding as an inert atmosphere.

Part 2 of 6Determining the percentage of oxygen

A fixed volume of air is passed back and forth over heated copper (or iron wool or phosphorus) in a sealed apparatus.

Determining the percentage of oxygen
The copper reacts with the oxygen: 2Cu + O2 → 2CuO.
The solid copper(II) oxide is black, and the gas volume decreases as oxygen is removed.
When the volume stops changing and the apparatus has cooled to room temperature, the final volume is measured.

Calculation

  • % oxygen = (volume lost ÷ original volume) × 100.
  • For example, if 100 cm3 of air falls to 79 cm3, oxygen = 21 cm3, which is 21%.
  • Using excess copper and cooling before reading are needed for an accurate result.

A simple version uses rustingiron wool dampened in a test tube inverted in water, in which the water level rises by about one fifth as oxygen is used.

Part 3 of 6Pollutants: sources and effects

Burning fossil fuels and vehicle engines release pollutants:

Pollutants: sources and effects
Carbon monoxide
(incomplete combustion): toxic, combines with haemoglobin and prevents it carrying oxygen.
Sulfur dioxide
(sulfur impurities in fuels): causes acid rain, damages buildings and aquatic life, and triggers respiratory problems.
Oxides of nitrogen
(high-temperature engines where nitrogen and oxygen react): cause acid rain and photochemical smog.
Carbon particles (soot)
Carbon particles (soot) global dimming and lung problems; unburnt hydrocarbons.

Catalytic converters in car exhausts convert carbon monoxide and nitrogen oxides to carbon dioxide and nitrogen: 2CO + 2NO → 2CO2 + N2.

Part 4 of 6Carbon dioxide, the greenhouse effect and climate change

Carbon dioxide is added by combustion of fossil fuels, respiration and deforestation, and removed by photosynthesis and absorption into oceans.

Greenhouse gases
Carbon dioxide and methane are greenhouse gases: they absorb infrared radiation emitted by the Earth’s surface and re-emit it, trapping heat.
Higher concentrations increase the greenhouse effect, causing global warming and climate change: rising sea levels, melting ice, more extreme weather and changes in habitats.

Reducing the effect

  • use renewable energy, plant trees, improve energy efficiency and use carbon capture.
  • Methane comes from cattle, rice paddies and landfill.

Part 5 of 6Sources of oxygen and the air as a resource

The present composition of the atmosphere has been stable for a long time.

Sources of oxygen and the air as a resource
Early in Earth’s history volcanic activity released carbon dioxide, water vapour and nitrogen.
As the planet cooled, water vapour condensed to form oceans, and plants and algae evolved.
Photosynthesis (carbon dioxide + water → glucose + oxygen) removed carbon dioxide and raised the oxygen level to about 21%, while carbon dioxide was also locked away in sedimentary rocks such as limestone and in fossil fuels.

Air is a raw materialfractional distillation of liquid air separates nitrogen (boiling point -196 °C), argon (-186 °C) and oxygen (-183 °C) because each has a different boiling point.

Sources of oxygen and the air as a resource
Nitrogen is used to make ammonia and as an inert packaging gas; oxygen is used in steel making, hospitals and welding.
Carbon dioxide is detected by limewater, which turns cloudy as calcium carbonate forms.

Part 6 of 6Worked examples

  1. A student heats 100 cm3 of air over excess copper. The volume falls to 79 cm3. Calculate the percentage of oxygen and explain why the apparatus must cool before the final reading. [3]3 marks

  2. Explain how a catalytic converter reduces pollution. [2]2 marks

  3. Explain how increased carbon dioxide leads to global warming. [3]3 marks

  4. Name the pollutant that causes acid rain and its source. [2]2 marks

Key terms

TermMeaning
MixtureSubstances physically mixed, not chemically bonded
Greenhouse gasGas that absorbs infrared radiation and warms the atmosphere
Incomplete combustionBurning in limited oxygen producing carbon monoxide and carbon
Acid rainRain made acidic by sulfur and nitrogen oxides
Catalytic converterExhaust device that converts harmful gases into less harmful ones
InertChemically unreactive

Avoid these mistakes

1
Saying air is a compound — it is a mixture.
2
Giving the proportion of oxygen as 78% — nitrogen is 78%.
3
Saying carbon dioxide causes the hole in the ozone layer.
4
Reading the gas volume before the apparatus has cooled.

Last updated:

\n