Subject: Integrated Science (Chapter 7)
Topic: Composition of Air & Gas Names
Subpage: 7.1A
Questions / Cues
- ❓ What is air and its main components?
- ❓ Can you spell all the main gas names correctly?
- ❓ What percentage of air does each gas account for?
A. Composition of Air & Gas Identification
• Air is a of gases. Its components are mixed without forming a new substance and are not chemically joined.
Spelling & Proportion Breakdown:
1. The most abundant gas in air is , making up about 78% of air.
2. The gas supporting human life and combustion is , which accounts for 21% of air.
3. Noble gases make up about 0.9% of air, including , , and .
4. The gas absorbed by green plants for photosynthesis is (0.03 – 0.04%).
5. The amount of in air varies from place to place depending on weather and humidity.
| Gas Component |
Percentage (%) |
| Nitrogen |
78% |
| Oxygen |
21% |
| Noble gases (Helium, Neon, Argon) |
0.9% |
| Carbon dioxide |
0.03 – 0.04% |
| Water vapour |
Variable |
Summary (Subpage 7.1A)
Air is an uncombined mixture of gases. Nitrogen accounts for the largest proportion (78%), followed by oxygen (21%). Small quantities of noble gases (such as argon, helium, and neon), carbon dioxide (0.03–0.04%), and variable amounts of water vapour complete the composition.
Subject: Integrated Science (Chapter 7)
Topic: Tests for Gases in Air
Subpage: 7.1B
Questions / Cues
- ❓ What reagents test for oxygen, CO₂, and nitrogen?
- ❓ How do we test for water or water vapour?
- ❓ How does nitrogen react with glowing splints and limewater?
B1. Tests for Oxygen, Carbon Dioxide & Nitrogen
• Oxygen: a .
• Carbon Dioxide: Turns clear and changes from red to yellow.
• Nitrogen: Extinguishes a , but produces no colour change with .
B2. Test for Water (Water Vapour)
• Test for water or water vapour by using , which changes from blue to .
Summary (Subpage 7.1B)
Testing reagents identify gases based on distinct reactions: oxygen relights a glowing splint, carbon dioxide turns clear limewater milky and hydrogencarbonate indicator yellow, while water vapour turns dry cobalt chloride paper from blue to pink. Nitrogen extinguishes a glowing splint without reacting with limewater.
Subject: Integrated Science (Chapter 7)
Topic: Properties & Uses of Gases in Air
Subpage: 7.2C
Questions / Cues
- ❓ Which gas supports respiration and combustion?
- ❓ Why is carbon dioxide used in fire safety and cooling?
- ❓ What key property makes nitrogen ideal for food packaging?
C1. Oxygen Properties & Applications
• Properties: Supports burning () and is essential for human survival.
• Applications: , rocket fuel, bottled oxygen for medical and high-altitude use.
C2. Carbon Dioxide Properties & Applications
• Properties: Does not support burning; denser than air; solid form () is extremely cold (-78 °C).
• Applications: Fire , keeping frozen food (e.g. ice cream) cold.
C3. Nitrogen Properties & Applications
• Properties: (inert) gas / does not support burning; liquid nitrogen is extremely cold (-196 °C).
• Applications: Food packaging to prevent food , freezing biological items (tissues, cells) or fruits requiring ultra-low temperatures.
Summary (Subpage 7.2C)
Oxygen supports combustion and respiration, enabling medical cylinders and welding applications. Carbon dioxide does not support burning and is dense, making it ideal for fire extinguishers and dry ice cooling. Unreactive nitrogen prevents food spoilage in sealed packaging and facilitates ultra-low temperature cell preservation.