1. Experiment Snapshot
| Feature | Details |
|---|
| Apparatus | Conical flask, thistle funnel if used, delivery tube, gas jar/test tube, bung. |
| Chemicals/Reagents | Calcium carbonate/marble chips, dilute hydrochloric acid, limewater. |
| Main observation | Effervescence occurs; carbon dioxide turns limewater milky. |
| Main measurement | Gas test observation. |
2. Aim
To prepare carbon dioxide gas and test it using limewater.
3. Quick Theory
Acids react with carbonates to produce salt, water and carbon dioxide. Carbon dioxide forms calcium carbonate with limewater, making it milky.
CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂
Examiner Tip: Carbon dioxide turns limewater milky.
4. Apparatus, Chemicals and Safety
| Category | Details |
|---|
| Apparatus | Conical flask, thistle funnel if used, delivery tube, gas jar/test tube, bung. |
| Chemicals | Calcium carbonate/marble chips, dilute hydrochloric acid, limewater. |
Safety: Wear goggles. Hydrochloric acid is irritant/corrosive. Do not inhale gases directly.
5. Labelled Experiment Diagram
Preparation and Testing of Carbon Dioxide — Premium Practical Setup
6. Procedure
- Place marble chips/calcium carbonate in a conical flask.
- Add dilute hydrochloric acid.
- Fit bung and delivery tube quickly.
- Bubble the gas through limewater.
- Observe limewater turning milky.
- Alternatively collect CO₂ by downward delivery if required.
- Record observations.
Examiner Tip: Do not use a burning splint as the main test; limewater is the key test.
7. Observations and Results
| Stage / Test | Observation | Conclusion |
|---|
| Reaction flask | Effervescence | CO₂ gas produced |
| Limewater | Turns milky | CO₂ present |
| Burning splint if used | Extinguished | CO₂ does not support combustion |
Conclusion: Carbon dioxide is prepared by acid-carbonate reaction and identified by turning limewater milky.
8. Calculations / Key Chemical Reasoning
Carbon dioxide reacts with calcium hydroxide in limewater to form insoluble calcium carbonate.
CO₂ + Ca(OH)₂ → CaCO₃ + H₂O
Worked Example:
The milky colour is due to solid calcium carbonate suspended in the limewater.
9. Sources of Error and Improvements
| Source of Error | Effect | Improvement |
|---|
| Apparatus leaks | Little gas reaches limewater | Check airtight setup |
| Acid too concentrated | Reaction too vigorous | Use dilute acid |
| Old limewater | Weak test | Use fresh limewater |
| Too much CO₂ passed | Milkiness may disappear | Record initial milky change |
| Tube not in limewater | No bubbling | Place delivery tube into limewater |
10. Student Common Mistakes
- Saying CO₂ relights glowing splint.
- Using hydrogen test.
- Forgetting limewater turns milky.
- Confusing marble chips with catalyst.
- Thinking milkiness is calcium chloride.
11. Examiner Tips
Tip: Acid + carbonate gives CO₂.
Tip: Limewater turns milky.
Tip: CO₂ extinguishes flame but limewater is better test.
Tip: Use fresh limewater.
12. Examiner Traps
Trap: Too much CO₂ can make milkiness disappear due to calcium hydrogencarbonate formation.
Trap: Marble chips are reactant, not catalyst.
Trap: CO₂ is denser than air.
13. 🎮 Interactive Simulator
Carbon Dioxide Limewater Test
Choose conditions and observe limewater.
Observation Window
Clear limewater
Choose a condition and run the simulation.
Lab Score: 0/0
14. Past Paper Style Questions
- State the aim of this experiment. [2 marks]
- Name the main apparatus or reagent used. [2 marks]
- Describe the key observation expected. [2 marks]
- Give one safety precaution. [1 mark]
- Give one source of error and one improvement. [2 marks]
- Explain the chemistry behind the result. [3 marks]
15. Mark Scheme Answers
Q1. To prepare and test carbon dioxide [2].
Q2. Marble chips, acid, delivery tube, limewater [2].
Q3. Fizzing and limewater turns milky [2].
Q4. Wear goggles when using acid [1].
Q5. Leak; seal apparatus [2].
Q6. Acid reacts with carbonate to form CO₂; CO₂ forms CaCO₃ in limewater [3].
16. Quick Revision Card
| Key Point | Memory Hook |
|---|
| Gas | CO₂ |
| Preparation | acid + carbonate |
| Test | limewater milky |
| Milky solid | CaCO₃ |
| Flame | extinguished |
17. Mastery Checklist
- I can prepare CO₂.
- I can state limewater test.
- I can write equations.
- I can identify errors.
- I can avoid gas-test confusion.