Air and Water
1. Air — The Invisible Blanket
Air is a MIXTURE of gases that surrounds the Earth. It is INVISIBLE, ODORLESS, and TASTELESS.
'We cannot SEE air, but we can FEEL it when the wind blows. We can PROVE it is there — a balloon filled with air has WEIGHT.'
Composition of Air
| Component | Percentage | Importance |
|---|---|---|
| Nitrogen | About 78% | Most ABUNDANT. Dilutes oxygen. Essential for plant growth (fixed by bacteria). |
| Oxygen | About 21% | ESSENTIAL for RESPIRATION (breathing) and burning. |
| Carbon dioxide | About 0.04% | Needed by plants for PHOTOSYNTHESIS. |
| Argon | About 0.93% | An INERT (noble) gas — does not react easily. |
| Water vapour | Varies (0-4%) | Needed for CLOUDS and RAIN. |
| Other gases | Traces | Neon, helium, methane, ozone, etc. |
| Dust particles | Varies | Help form CLOUDS (water droplets collect around dust). |
'Remove the oxygen from air and you cannot BREATHE. Remove the nitrogen and everything would BURN too fast. Remove carbon dioxide and plants would STARVE. Every gas in the air has a PURPOSE.'
Properties of Air
| Property | Demonstration |
|---|---|
| Air OCCUPIES space | A balloon inflates. An upside-down glass pushed into water stays DRY inside. |
| Air has WEIGHT | A balloon weighs MORE when inflated than when deflated. |
| Air EXERTS pressure | A straw works because air pressure pushes the liquid UP. |
| Air can be COMPRESSED | A bicycle pump compresses air into the tyre. |
| Air EXPANDS when heated | Hot air balloons rise because hot air is lighter. |
2. Atmosphere — Layers of Air Around Earth
The ATMOSPHERE is the LAYER of air surrounding the Earth. It has FIVE main layers.
| Layer | Height (approx.) | Key Features |
|---|---|---|
| Troposphere | 0-12 km | We LIVE here. WEATHER happens here. Contains MOST of the air. Temperature DECREASES with height. |
| Stratosphere | 12-50 km | Contains the OZONE LAYER. Airplanes fly here. Temperature INCREASES with height. |
| Mesosphere | 50-80 km | METEORS burn up here. Coldest layer. |
| Thermosphere | 80-700 km | AURORAS (Northern/Southern Lights) occur here. Very HIGH temperatures. |
| Exosphere | 700-10,000 km | Outermost layer. Air is VERY thin. Satellites orbit here. |
The Ozone Layer
'THE OZONE LAYER in the stratosphere acts like a SUNSCREEN for the Earth. It ABSORBS most of the Sun's harmful ULTRAVIOLET (UV) rays, protecting all life on Earth.'
| Ozone Fact | Detail |
|---|---|
| What is it? | A layer of OZONE gas (O₃) in the stratosphere |
| What does it do? | Absorbs 99% of harmful UV radiation from the Sun |
| What damages it? | CFCs (chlorofluorocarbons) from old refrigerators, air conditioners, and aerosol sprays |
| Current status | The ozone hole is HEALING because CFCs were banned |
3. Water — The Elixir of Life
Water covers about 71% of the Earth's surface. The human body is about 60% water.
'Water is the ONLY substance on Earth that naturally exists in ALL three states — solid (ice), liquid (water), and gas (water vapour).'
Distribution of Water on Earth
| Type | Percentage | Where |
|---|---|---|
| Salt water (oceans) | About 97% | Oceans and seas — NOT drinkable |
| Fresh water | About 3% | Rivers, lakes, glaciers, groundwater |
| Available for humans | Less than 1% | Very SMALL fraction of total water |
4. The Water Cycle
The WATER CYCLE is the continuous MOVEMENT of water between the Earth's surface and the atmosphere.
| Process | What Happens | State Change |
|---|---|---|
| Evaporation | Sun heats water in oceans, rivers, and lakes → turns to water vapour (gas) | Liquid → Gas |
| Transpiration | Plants release water vapour through their LEAVES | Liquid → Gas |
| Condensation | Water vapour rises, COOLS, and turns back into tiny water droplets | Gas → Liquid |
| Precipitation | Water droplets become heavy → fall as RAIN, SNOW, or HAIL | Gas → Liquid (or solid) |
| Collection | Water collects in oceans, rivers, lakes, and soil | Cycle CONTINUES |
'The water you drink today may have been part of a DINOSAUR's bath millions of years ago! Water on Earth is RECYCLED over and over — the same water has been cycling for BILLIONS of years.'
5. Purification of Water
Not all water is SAFE to drink. Contaminated water causes DISEASES like cholera, typhoid, and diarrhoea.
Methods of Purification
| Method | How It Works | Removes |
|---|---|---|
| Boiling | Heat water to 100°C | KILLS germs and bacteria |
| Filtration | Pass water through a FILTER (sand, charcoal, cloth) | Removes DIRT and PARTICLES |
| Sedimentation | Let water STAND — heavy particles SETTLE at the bottom | Removes SAND and MUD |
| Chlorination | Add CHLORINE tablets or liquid | KILLS GERMS |
| Distillation | Boil water → collect STEAM → condense | Removes ALL impurities (including salt) |
| RO (Reverse Osmosis) | Force water through a special MEMBRANE | Removes DISSOLVED salts and chemicals |
'In an EMERGENCY, the SAFEST way to purify water is to BOIL it for at least 10 minutes. This kills ALL disease-causing germs. Let it COOL before drinking.'
6. Air and Water Pollution
Air Pollution
When HARMFUL substances (pollutants) mix with the air, it becomes POLLUTED.
| Source of Air Pollution | Effect |
|---|---|
| Vehicle exhaust | Carbon monoxide, nitrogen oxides — breathing problems |
| Factory smoke | Sulphur dioxide — acid rain, respiratory diseases |
| Burning of garbage | Toxic fumes — cancer, lung diseases |
| Deforestation | More CO₂ — global warming |
| CFCs | Ozone layer DEPLETION |
Water Pollution
When HARMFUL substances enter water bodies, the water becomes POLLUTED.
| Source of Water Pollution | Effect |
|---|---|
| Industrial waste | Toxic chemicals kill aquatic life |
| Sewage | Disease-causing germs — cholera, typhoid |
| Agricultural runoff | Fertilisers and pesticides poison water |
| Plastic waste | Marine animals EAT plastic and DIE |
| Oil spills | Coats birds and fish — suffocates them |
Key Facts to Remember
- Air is a MIXTURE of gases: 78% nitrogen, 21% oxygen, 0.04% carbon dioxide.
- The atmosphere has FIVE layers. The troposphere is where weather occurs.
- The ozone layer PROTECTS us from UV radiation.
- 97% of Earth's water is SALT water. Only 3% is fresh.
- 'The water cycle is a CLOSED system — no NEW water is created. The same water has been cycling for billions of years.'
- Boiling is the SIMPLEST way to purify water at home.
Common Mistakes
| Mistake | Why It Is Wrong | Correct Understanding |
|---|---|---|
| Thinking air is mostly oxygen | Oxygen is only 21% | Nitrogen is the major component (78%) |
| Believing water on Earth is endless | Only 1% of water is easily accessible fresh water | Water SCARCITY is a serious problem |
| Confusing weather and atmosphere layers | Weather happens ONLY in the troposphere | The stratosphere is too stable for weather |
| Thinking all water purification methods remove everything | Filtration does NOT remove dissolved chemicals or germs | Boiling or distillation is needed for killing germs |
Exam Focus (ICSE Class 5)
| Topic | Marks (Typical) | Question Type |
|---|---|---|
| Composition of air | 3-4 marks | Percentage of gases / properties |
| Atmosphere layers | 3-4 marks | Name layers and features |
| Water cycle | 4-5 marks | Label diagram / explain processes |
| Water purification | 3-4 marks | Methods and what they remove |
| Pollution — causes and effects | 3-4 marks | Sources and their impacts |
Self-Test: 5 Questions
Q1. Name the four most abundant gases in air and their approximate percentages.
Q2. Draw and label the water cycle. Explain evaporation and condensation.
Q3. Why is it important to purify water before drinking? Name two methods.
Q4. What is the ozone layer? Why is it important?
Q5. List three causes of air pollution and three causes of water pollution.
Answers
A1. Nitrogen (78%), Oxygen (21%), Argon (0.93%), Carbon dioxide (0.04%).
A2. The water cycle: Sun → Evaporation (water turns to vapour) → Condensation (vapour cools to form clouds) → Precipitation (rain/snow) → Collection (water returns to oceans/rivers) → Repeat.
A3. Water must be purified to remove GERMS and IMPURITIES that cause diseases. Two methods: BOILING (kills germs) and FILTRATION (removes particles).
A4. The ozone layer is a layer of OZONE (O₃) in the stratosphere. It ABSORBS harmful UV (ultraviolet) radiation from the Sun, protecting living things from skin cancer, eye damage, and other harm.
A5. Air pollution: Vehicle exhaust, factory smoke, burning garbage. Water pollution: Industrial waste, sewage, plastic waste.
