CIE iGCSE Co-Ordinated Science C9.5 Corrosion of metals Exam Style Questions Paper 2
Question
A piece of iron is coated with a layer of zinc.
Which statement explains why zinc prevents iron from rusting, even when the layer of zinc is damaged?
A Iron is less reactive than zinc and zinc atoms lose electrons less easily than iron atoms.
B Iron is less reactive than zinc and zinc atoms lose electrons more easily than iron atoms.
C Iron is more reactive than zinc and zinc atoms lose electrons less easily than iron atoms.
D Iron is more reactive than zinc and zinc atoms lose electrons more easily than iron atoms.
▶️Answer/Explanation
Ans : B
Question
Zinc is used to galvanise iron. Which statements about galvanising are correct?
- Iron is more reactive than zinc.
- Zinc oxidises instead of iron.
- Galvanised iron rusts if the zinc coating is scratched.
- Galvanising iron is an example of sacrificial protection.
| A | 1 and 2 |
| B | 1 and 3 |
| C | 2 and 4 |
| D | 3 and 4 |
▶️Answer/Explanation
Answer: C
Explanation: Zinc is more reactive than iron, so it oxidises instead of iron, providing sacrificial protection. Galvanising is indeed an example of sacrificial protection. However, if the zinc coating is scratched, the iron underneath can still rust, so statement 3 is incorrect.
Question
A block of zinc is attached to an underground steel pipe as shown.
The zinc stops the steel rusting by sacrificial protection. Which statement is not correct?
A: Zinc is more reactive than the iron in steel.
B: Zinc is oxidised in preference to the iron in steel.
C: Zinc prevents oxygen from reaching the steel.
D: Zinc transfers electrons to the iron in the steel.
▶️Answer/Explanation
Answer: C
Explanation: Zinc does not prevent oxygen from reaching the steel. Instead, it acts as a sacrificial anode, being oxidized in preference to the iron, thus protecting the steel from rusting.