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CIE iGCSE Co-Ordinated Science C9.5 Corrosion of metals Exam Style Questions Paper 2

CIE iGCSE Co-Ordinated Science Paper 2 - All Chapters

Question

Which statements explain why zinc is used to galvanise steel?

  1. It is less reactive than steel.
  2. It forms an alloy with steel.
  3. It prevents air and water coming into contact with steel.
  4. It provides sacrificial protection for the steel.

A. 1 and 2
B. 1 and 4
C. 2 and 3
D. 3 and 4

▶️ Answer/Explanation
Zinc galvanising protects steel in two ways: it acts as a barrier coating preventing air and water from reaching the steel (statement 3), and if the coating is scratched, zinc provides sacrificial protection because it is more reactive than iron and corrodes preferentially (statement 4). Zinc is more reactive than steel, not less (statement 1 is wrong), and galvanising is a coating, not an alloy (statement 2 is wrong).
✅ Answer: (D)

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
Zinc is more reactive than iron, which means iron is less reactive than zinc.
Being more reactive means zinc atoms lose electrons more easily than iron atoms, forming ions more readily.
Because zinc loses electrons in preference to iron, it corrodes first and protects the iron even where the coating is scratched, a process called sacrificial protection.
✅ Answer: (B)

Question 

Zinc is used to galvanise iron. Which statements about galvanising are correct?

  1. Iron is more reactive than zinc.
  2. Zinc oxidises instead of iron.
  3. Galvanised iron rusts if the zinc coating is scratched.
  4. 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.

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