Year 9 Science · Unit 2 · Lesson 03
Challenge Worksheet
Learning Goals
Evaluate the claim
Someone claims…
"A hardware company markets 'rustproof' iron garden stakes. The product description says: 'Our stakes are coated with a revolutionary non-reactive polymer skin, making them chemically inert, iron cannot corrode because it has no contact with oxygen or water.' After two summers in a NSW garden, customers report the stakes are heavily rusted around the base where the coating has chipped. The company insists this is 'misuse' rather than a product failure."
(a) Identify which part of the company's original claim is scientifically accurate. Explain why the protection method described (polymer coating) should, in principle, prevent rusting.
(b) Using your knowledge of iron's chemical properties and the rusting process, explain why chipping of the coating causes rapid corrosion near the base, where the stakes are inserted into moist soil.
(c) Suggest a better protection strategy for iron garden stakes that would remain effective even if the surface is scratched. Name the strategy, explain the science behind it, and identify one trade-off compared to a simple paint coating.
1. A government report recommends replacing iron water pipes in older suburbs with gold pipes because "gold is totally non-reactive and safe." Evaluate this recommendation: identify one scientific advantage and at least one major reason why it would not be adopted in practice. Use the reactivity series in your answer.
2. Stainless steel contains 10–12% chromium, which forms a self-healing chromium oxide barrier. A student claims "stainless steel doesn't corrode because it has no chemical properties." Identify the error in this reasoning and write a scientifically accurate explanation of why stainless steel resists corrosion.
Wrap Up
In one sentence, what was the main idea of this lesson?