Chemistry in Daily Life — Class 7 Science (Samacheer Kalvi)
TN State Board (Samacheer Kalvi) Class 7 Science, Term 3 — Chapter 4. Medicines, combustion and fire safety.
1. About this chapter
This chapter covers medicines, combustion and the fire triangle, ignition temperature, the flame, and fire safety.
2. Medicines
| Medicine | Use |
|---|---|
| Analgesic | relieves pain |
| Antipyretic | lowers fever (temperature) — e.g. aspirin |
| Antibiotic | kills bacteria — e.g. penicillin (treats pneumonia, bronchitis) |
| Antacid | neutralises stomach acid |
- Antibiotics do not work against viruses such as the common cold and flu.
3. Combustion and the fire triangle
- Combustion (burning) needs three things — fuel, heat and oxygen (the fire triangle). Oxygen is necessary for combustion.
- The ignition temperature is the lowest temperature at which a substance catches fire.
- Not all fuels burn with a flame — only fuels that vaporise produce a flame (a candle burns with a flame; charcoal mostly glows).
4. The flame and fire safety
- A candle flame has zones: the innermost (dark) zone is unburnt vapour, the middle (yellow) zone is partly burnt, and the outermost zone is fully burnt — the hottest part of a candle flame is the blue (outermost) region.
- Burning wood and coal pollutes the air. A fire extinguisher puts out a fire by removing one part of the fire triangle (cutting off heat or oxygen) — water cools; CO₂ cuts off oxygen.
5. Worked examples
Example 1. Which medicine lowers fever? An antipyretic (e.g. aspirin).
Example 2. What three things are needed for fire? Fuel, heat and oxygen.
Example 3. Which is the hottest part of a candle flame? The blue (outermost) zone.
6. Book-back questions (Samacheer Kalvi)
I. Choose the correct answer
- A drug used to treat pneumonia and bronchitis is — (a) penicillin / (b) aspirin. Ans: (a) penicillin.
- Aspirin is an — (a) antibiotic / (b) antipyretic. Ans: (b) antipyretic.
- A substance that neutralises stomach acid is an — (a) antacid / (b) analgesic. Ans: (a) antacid.
- The lowest temperature at which a substance catches fire is its — (a) boiling point / (b) ignition temperature. Ans: (b) ignition temperature.
- The hottest part of a candle flame is the — (a) yellow zone / (b) blue zone. Ans: (b) blue zone.
II. True or False 6. Antibiotics work against viruses like cold and flu. — False (they work against bacteria). 7. Analgesics lower the temperature during fever. — False (antipyretics do). 8. Oxygen is necessary for combustion. — True. 9. Burning wood and coal pollutes the air. — True.
III. Answer briefly 10. What are the three requirements for fire? — Fuel, heat and oxygen (the fire triangle). 11. How does a fire extinguisher work? — By removing one part of the fire triangle (cutting off heat or oxygen).
7. Common mistakes
- Mistake: Taking antibiotics for a cold or flu. Fix: Antibiotics treat bacteria, not viruses (cold and flu are viral).
- Mistake: Confusing analgesic and antipyretic. Fix: Analgesic = pain relief; antipyretic = lowers fever.
- Mistake: Saying the yellow part of a flame is the hottest. Fix: The blue (outermost) zone is the hottest.
8. Quick revision
- Term 3 · Ch 4 · chemistry in daily life.
- Medicines: analgesic (pain), antipyretic (fever, aspirin), antibiotic (bacteria, penicillin), antacid (stomach acid). Antibiotics don't work on viruses.
- Combustion needs fuel + heat + oxygen; ignition temperature = lowest temp to catch fire; not all fuels form a flame.
- Hottest part of a candle flame = blue zone; burning wood/coal pollutes air; extinguisher removes part of the fire triangle.
