Year 9 Science · Unit 2 · Lesson 03
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Learning Goals
Because… chain
Fill in the missing effects. Each cause leads to the next step in the rusting of iron.
Overall outcome:
Predict + reason
Scenario
A civil engineer in coastal NSW is choosing between plain steel, galvanised steel, and stainless steel for outdoor fencing that will be exposed to salt spray near the ocean. Iron corrodes 10 times faster near the ocean than inland because dissolved salts speed up the electrochemical rusting reaction. The engineer knows that zinc (galvanising) is higher in the reactivity series than iron, and that stainless steel contains 10–12% chromium which forms a self-healing chromium oxide barrier.
(a) Explain why plain steel would be a poor choice for this coastal fencing application, using your knowledge of iron's chemical properties and the corrosion process.
(b) Explain how galvanised steel protects the underlying iron from rusting. Use the concept of the reactivity series and sacrificial protection in your answer.
1. The Sydney Harbour Bridge is continuously repainted to prevent corrosion. Using your knowledge of iron's chemical properties, explain why paint is necessary and what would happen if repainting stopped.
2. A steel fence post is galvanised with zinc. The zinc layer is scratched, exposing a small patch of steel. Predict whether the steel will rust quickly or slowly, and explain why, using the concept of sacrificial protection.
Wrap Up
In one sentence, what was the main idea of this lesson?