Topic: Metals – Corrosion of Metals
Lesson 1: Rusting of Iron and Steel
| Section | Details |
|---|---|
| Objective | State the conditions required for the rusting of iron and steel to form hydrated iron(III) oxide. |
| Activities | – Starter (5 mins): Show rusted iron objects and ask: “What do you think causes iron to rust?”- Main (25 mins): 1. Explain that rusting requires the presence of both oxygen and water. 2. Describe the chemical reaction: 4Fe+3O2+6H2O→4Fe(OH)34\text{Fe} + 3\text{O}_2 + 6\text{H}_2\text{O} → 4\text{Fe(OH)}_3, which dehydrates to form hydrated iron(III) oxide. 3. Discuss how rust weakens iron and steel, leading to damage over time.- Plenary (10 mins): Students complete a diagram labeling the conditions necessary for rusting. |
| Resources | Rusted iron samples, reaction equations, worksheets. |
| Time | 40 minutes total: 5 mins (Starter) + 25 mins (Main) + 10 mins (Plenary). |
| Homework | Write a short explanation of why rusting occurs more quickly in coastal areas. |
| Assessment | Worksheet: Identify and explain the conditions required for rusting based on scenarios. |
| Past Paper Practice | IGCSE Chemistry 0620/41/M/J/20 Q6(c) – Conditions for rusting. |
Lesson 2: Preventing Rusting – Barrier Methods
| Section | Details |
|---|---|
| Objective | Describe how barrier methods prevent rusting by excluding oxygen or water. State common barrier methods, including painting, greasing, and coating with plastic. |
| Activities | – Starter (5 mins): Ask: “How can we protect a piece of iron from rusting?”- Main (25 mins): 1. Define barrier methods as methods that exclude oxygen and water. 2. Discuss common barrier methods: – Painting: Ideal for large structures like bridges. – Greasing: Used for moving parts like machinery. – Plastic coating: Protects surfaces exposed to moisture. 3. Provide real-life examples of these methods.- Plenary (10 mins): Students complete a table matching barrier methods to their applications and advantages. |
| Resources | Images or examples of barrier methods, worksheets. |
| Time | 40 minutes total: 5 mins (Starter) + 25 mins (Main) + 10 mins (Plenary). |
| Homework | Write a paragraph explaining which barrier method you would use to protect a car and why. |
| Assessment | Worksheet: Match rust prevention methods to given situations and explain their effectiveness. |
| Past Paper Practice | IGCSE Chemistry 0620/41/O/N/21 Q5(b) – Barrier methods for preventing rust. |
Lesson 3: Sacrificial Protection and Galvanising
| Section | Details |
|---|---|
| Objective | Explain sacrificial protection in terms of the reactivity series and electron loss. Describe the use of zinc in galvanising as an example of a barrier method and sacrificial protection. |
| Activities | – Starter (5 mins): Ask: “Why does a coating of zinc on iron prevent it from rusting, even if it gets scratched?”- Main (25 mins): 1. Define sacrificial protection: A more reactive metal (e.g., zinc) corrodes in place of the protected metal. 2. Explain in terms of the reactivity series: Zinc loses electrons more readily than iron, protecting it from oxidation. 3. Discuss galvanising: Coating iron with zinc provides both a barrier and sacrificial protection. 4. Provide examples of galvanised items (e.g., roofing sheets, water pipes).- Plenary (10 mins): Students summarize the process of sacrificial protection and its advantages. |
| Resources | Samples of galvanised items, diagrams of sacrificial protection, worksheets. |
| Time | 40 minutes total: 5 mins (Starter) + 25 mins (Main) + 10 mins (Plenary). |
| Homework | Write a short explanation of why zinc corrodes instead of iron when exposed to moisture. |
| Assessment | Worksheet: Explain how sacrificial protection works in specific scenarios (e.g., ships, pipelines). |
| Past Paper Practice | IGCSE Chemistry 0620/41/M/J/19 Q6(a) – Sacrificial protection and galvanising. |
Lesson 4: Experimental Investigation of Rusting
| Section | Details |
|---|---|
| Objective | Deduce the effectiveness of rust prevention methods from experimental results. |
| Activities | – Starter (5 mins): Ask: “How can we test which rust prevention method works best?”- Main (25 mins): 1. Set up an experiment with iron nails in different conditions (e.g., exposed to air and water, coated with grease, covered with zinc). 2. Observe and record the extent of rusting over time. 3. Discuss findings and relate them to the effectiveness of the methods.- Plenary (10 mins): Students analyze the results and rank the methods from most to least effective. |
| Resources | Iron nails, water, grease, paint, zinc coating, beakers, worksheets. |
| Time | 40 minutes total: 5 mins (Starter) + 25 mins (Main) + 10 mins (Plenary). |
| Homework | Write a lab report summarizing the results of the rust prevention experiment. |
| Assessment | Lab report: Analyze the effectiveness of rust prevention methods based on experimental results. |
| Past Paper Practice | IGCSE Chemistry 0620/41/O/N/20 Q5(c) – Experimental investigation of rusting. |
Key Notes for Students:
- Rusting Conditions:
- Requires oxygen and water to form hydrated iron(III) oxide.
- Barrier Methods:
- Prevent rusting by excluding oxygen and water.
- Examples: Painting, greasing, plastic coating.
- Sacrificial Protection:
- Uses a more reactive metal (e.g., zinc) to protect iron.
- Galvanising: Combines barrier and sacrificial protection.
- Applications:
- Galvanised roofs, water pipes, and ship hulls use sacrificial protection to prevent corrosion.
Notes for Teachers:
- Use hands-on experiments to engage students and reinforce concepts.
- Provide real-life examples of rust prevention for better understanding.
- Relate the concepts of rusting and prevention to industrial and everyday applications.
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