Year 9 Science · Unit 2 · Lesson 03
Apply Worksheet
Learning Goals
Match each protection method to how it works
Write the letter of the matching description in the middle column.
| Method | Letter | How it works |
|---|---|---|
| Galvanising | A. Keeps oxygen and water away with a coating that must be renewed. | |
| Anodising | B. Coats steel with zinc, which corrodes first because it is more reactive than iron. | |
| Painting | C. Adds chromium, which forms a thin, self-healing oxide layer on the surface. | |
| Alloying (stainless steel) | D. Uses electricity to thicken the natural oxide layer on aluminium. |
1. What is the chemical name for rust?
Cause and effect
Fill the two empty boxes. Each arrow means “which causes”.
2. Scratching the paint off the gate is a physical change, but rust forming on the bare steel is a chemical change. Explain the difference, using these two examples.
Data: a reactivity test
Small strips of four metals, all the same size, went into equal volumes of one dilute acid. Students counted hydrogen bubbles over the first 30 seconds.
| Metal | Zinc | Copper | Magnesium | Iron |
|---|---|---|---|---|
| Bubbles counted | 21 | 0 | 48 | 6 |
Source: sample class results.
3. List the four metals from most reactive to least reactive.
4. A fence made of iron can be protected by a metal that corrodes in its place. Which metals in Table 1 could do this, and why could copper not? Use the data.
Scenario: a coastal fence
A civil engineer in coastal NSW is choosing between plain steel, galvanised steel and stainless steel for an outdoor fence that will be sprayed with salt water from the ocean. Salt speeds up the rusting reaction.
5. Explain why plain steel would be a poor choice for this fence.
6. The zinc layer on a galvanised fence post is scratched, exposing a small patch of steel. Predict whether the exposed steel will rust quickly or slowly, and explain why.
7. Recommend one of the three materials for the coastal fence. Compare all three and justify your choice.