Final Exam Readiness Checklist
📊 Master Summary Table: Air and its Constituents
| Constituent | Percentage (Approx.) | Key Function / Use | Identification Test |
| Nitrogen ($N_2$) | 78.03% | Dilutes oxygen; used to preserve food and make fertilizers. | Does not support combustion; no reaction with limewater. |
| Oxygen ($O_2$) | 20.9% | Essential for respiration and combustion. | A glowing splint bursts into flame. |
| Noble Gases (e.g., Argon) | 0.94% | Used in advertising signs and electric bulbs (Inert). | Chemically inactive; does not react with common reagents. |
| Carbon Dioxide ($CO_2$) | 0.03% | Essential for photosynthesis; used in fire extinguishers. | Turns freshly prepared limewater milky. |
| Water Vapour ($H_2O$) | Variable | Influences weather/climate; prevents drying of tissues. | Turns white anhydrous copper sulphate blue. |
| Dust & Smoke | Variable | Provides nuclei for water vapour to condense into rain. | Observed as tiny moving particles in a beam of light. |
⚡ Quick Revision: The "Big Three" Experiments
1. The Candle and Jar Experiment
Purpose: To prove air (oxygen) is necessary for combustion.
Action: Cover a burning candle with a glass.
Observation: The flame dies out after a few seconds.
Conclusion: Only a limited amount of oxygen was available.
2. The Limewater Test
Purpose: To detect Carbon Dioxide ($CO_2$).
Action: Bubble air or combustion products through clear limewater.
Observation: The liquid turns cloudy/milky.
Conclusion: CO2 is present.
3. The Copper Sulphate Test
Purpose: To detect Water Vapour (H2O).
Action: Pass gases through white anhydrous copper sulphate.
Observation: The white powder turns blue.
Conclusion: Water vapour is present.
💡 Final Exam Hack:
If you are asked to distinguish between Respiration and Combustion:
Respiration is a slow oxidation occurring inside living cells.
Combustion is a fast oxidation occurring at high temperatures outside.
Commonality: Both use Oxygen and release Carbon Dioxide and Water Vapour!
This Final Exam Readiness Checklist is designed to give your students a clear roadmap for their revision. It covers every major concept and investigation from Chapter 5.
✅ Final Exam Readiness Checklist: Air and Atmosphere
1. Fundamental Concepts
[ ] I can define Atmosphere and describe it as a mixture of gases.
[ ] I know the exact percentages of Nitrogen ($78.03\%$), Oxygen ($20.9\%$), and Carbon Dioxide ($0.03\%$).
[ ] I can explain why Nitrogen is considered inert and how it is used in food preservation.
[ ] I can distinguish between Combustion (fast oxidation) and Respiration (slow oxidation).
2. Practical Investigations (5.1 – 5.4)
[ ] Water Vapour in Air: I can explain why droplets form on a cold glass of ice.
[ ] Carbon Dioxide in Air: I can describe the limewater test and why it turns "milky."
[ ] Oxygen for Burning: I can explain why a candle goes out when covered by a jar.
[ ] Products of Combustion: I can identify that both $CO_2$ and $H_2O$ are released when a fuel burns.
3. Chemical Tests & Observations
[ ] Oxygen: I know a glowing splint will rekindle in its presence.
[ ] Water Vapour: I know white Anhydrous Copper Sulphate turns blue.
[ ] Carbon Dioxide: I know clear Limewater turns milky/cloudy.
4. Applied Knowledge
[ ] I can explain why water rises in a jar (to fill the vacuum left by consumed oxygen).
[ ] I can list properties of a Good Fuel (cheap, high heat, no residue).
[ ] I understand how Photosynthesis and Respiration balance the gases in our atmosphere.
🏆 Final Challenge: The 60-Second Review
Before you close your book, try to answer these three questions from memory:
What is the chemical formula for the "milky" substance in limewater? (Answer: Calcium Carbonate)
Which gas is used to "dilute" oxygen in our air? (Answer: Nitrogen)
What happens to copper sulphate when it becomes hydrated? (Answer: It turns white to blue)
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