1. Experiment Snapshot
| Feature | Details |
|---|
| Apparatus | Electrolysis cell, DC power supply, copper electrodes, wires, beaker. |
| Chemicals/Reagents | Copper sulfate solution, dilute sulfuric acid if used. |
| Main observation | Impure copper anode dissolves; pure copper deposits on cathode; sludge forms below anode. |
| Main measurement | Change in mass/appearance of electrodes. |
2. Aim
To purify impure copper using electrolysis.
3. Quick Theory
Impure copper is oxidised at the anode to Cu²⁺ ions. These ions move through solution and are reduced at the pure copper cathode.
Anode: Cu → Cu²⁺ + 2e⁻ ; Cathode: Cu²⁺ + 2e⁻ → Cu
Examiner Tip: In copper purification, impure copper is the anode and pure copper is the cathode.
4. Apparatus, Chemicals and Safety
| Category | Details |
|---|
| Apparatus | Electrolysis cell, DC power supply, copper electrodes, wires, beaker. |
| Chemicals | Copper sulfate solution, dilute sulfuric acid if used. |
Safety: Wear goggles. Copper sulfate is harmful/irritant. Use low-voltage DC supply.
5. Labelled Experiment Diagram
Purification of Copper — Premium Practical Setup
6. Procedure
- Set up a beaker containing copper sulfate solution.
- Place impure copper as the anode.
- Place a thin sheet of pure copper as the cathode.
- Connect to a DC power supply.
- Switch on current for a suitable time.
- Observe the anode dissolving and copper depositing on cathode.
- Observe any anode sludge below the impure copper.
- Switch off and compare electrodes.
Examiner Tip: Do not swap the electrodes: impure copper must be the anode.
7. Observations and Results
| Stage / Test | Observation | Conclusion |
|---|
| Anode | Impure copper gets smaller | Copper atoms form Cu²⁺ ions |
| Cathode | Pure copper layer grows | Cu²⁺ ions deposit as copper |
| Bottom of cell | Sludge forms | Insoluble impurities collect |
Conclusion: Electrolysis transfers copper from the impure anode to the pure cathode, leaving impurities behind.
8. Calculations / Key Chemical Reasoning
The same copper half-equation appears in opposite directions at the two electrodes.
Cu → Cu²⁺ + 2e⁻ ; Cu²⁺ + 2e⁻ → Cu
Worked Example:
Copper atoms from the anode enter solution as Cu²⁺; Cu²⁺ ions gain electrons at the cathode to form pure copper.
9. Sources of Error and Improvements
| Source of Error | Effect | Improvement |
|---|
| Electrodes reversed | Wrong process | Label anode/cathode |
| Current too high | Poor copper deposit | Use controlled current |
| Electrodes touching | Short circuit | Keep separated |
| Cathode dirty | Poor adhesion | Clean cathode |
| Not enough time | Small visible change | Run longer safely |
10. Student Common Mistakes
- Putting pure copper at anode.
- Forgetting anode sludge.
- Saying impurities plate onto cathode.
- Confusing with copper sulfate using inert electrodes.
- Forgetting anode loses mass.
11. Examiner Tips
Tip: Impure copper is anode.
Tip: Pure copper is cathode.
Tip: Anode sludge contains impurities.
Tip: Copper deposits at cathode.
12. Examiner Traps
Trap: This process uses copper electrodes, not inert electrodes.
Trap: The electrolyte remains copper sulfate.
Trap: Impurities do not usually deposit as pure copper.
13. 🎮 Interactive Simulator
Copper Purification Cell
Choose conditions and observe electrode changes.
Observation Window
Cu refining
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 purify impure copper by electrolysis [2].
Q2. Copper sulfate, impure copper anode, pure copper cathode, DC supply [2].
Q3. Anode dissolves; copper deposits at cathode [2].
Q4. Wear goggles/handle copper sulfate safely [1].
Q5. Electrodes reversed; label correctly [2].
Q6. Copper oxidises at anode and Cu²⁺ reduces at cathode [3].
16. Quick Revision Card
| Key Point | Memory Hook |
|---|
| Anode | Impure copper |
| Cathode | Pure copper |
| Electrolyte | Copper sulfate |
| Impurities | Anode sludge |
| Cathode change | Gains mass |
17. Mastery Checklist
- I can identify anode and cathode.
- I can write half equations.
- I can explain anode sludge.
- I can compare with copper sulfate electrolysis.