1. CHAPTER 5
The composition of air

2. Air is a mixture of various substances that is odourless, colourless, or tasteless
Water vapour in the air depends on the humidity in the air.
The more humid the air, the more the water vapour in the air
Examples of inert gases are:
Dust
Water vapour
Microorganisms
The composition of air

3. The properties of oxygen and carbon dioxide
Air is made up of three main gases: oxygen, carbon dioxide and nitrogen
Each gas has its own chemical properties
The properties of the gases can be observed by :
Solubility in the water
Reaction with sodium hydroxide
Effects on
Glowing wooden splinter
Burning wooden splinter
Litmus paper
Lime water
Hydrogen carbonate indicator
Nitrogen is a gas that does not react chemically
The properties of oxygen and carbon dioxide

4. Oxygen is needed for respiration
Air that is breathed into the body is called inhaled air
Air that is breathed out of the body is called exhaled air
Oxygen is needed for respiration:
Inhaled oxygen will be dissolved at the surface of the moist alveolus.
Oxygen will be absorbed into the blood capillary through the thin alveolus wall
Oxygen is then transported by red blood cells to the other blood cells for the process of respiration
At the same time, carbon dioxide and water from blood capillaries will be absorbed alveolus.
Carbon dioxide and water will be expelled body when air is exhaled.
Oxygen is needed for respiration

5. Oxygen is needed for combustion
Combustion is a process that takes place when a substance unites with oxygen chemically and this produces energy and light.
Without oxygen. Combustion cannot occur because chemical process does not take place.
Carbon is a chemical compound that is made up of the carbon element only
Combustion of carbon releases carbon dioxide, heat energy and light energy.
Examples of carbon are wood, cloth, charcoal, and paper.
Carbon + Oxygen Carbon dioxide + Heat energy + Light energy
Hydrocarbon is a chemical compound which is formed from only hydrogen and carbon.
Oxygen is needed for combustion

6. Oxygen is needed for combustion (CONTINUE)
Combustion of hydrocarbon produces carbon dioxide, water, heat energy and light energy.
Water is formed when hydrogen from hydrocarbon combines with oxygen during combustion.
Hydrocarbon + Carbon Carbon Dioxide +Water +Heat energy + Light energy
Combustion produces light energy and heat energy
Carbon dioxide produced is absorbed by green plants to conduct photosynthesis.
Oxygen is needed for combustion (CONTINUE)