STUDENT SPACE · TOPIC 5

Corrosion and protection

Explain rust prevention, galvanising and aluminium’s oxide layer.

The essentials

Iron and steel rust when both oxygen and water are present. Rust is hydrated iron(III) oxide.
Only the condition with both water and oxygen should produce rust.
Paint, grease and plastic coatings protect iron by excluding oxygen or water.

Try each question before opening its hint or answer. Use paper for calculations and diagrams.

Why can aluminium resist corrosion despite being above iron in the reactivity series?

Need a hint for Question 1?

Identify whether protection comes from a barrier, sacrifice or both.

Check Question 1

Its thin, adherent oxide layer acts as a protective barrier.

State the two conditions required for rusting and name the rust product.

Need a hint for Question 2?

Distinguish damp air from dry air.

Check Question 2

Water and oxygen. Rust is hydrated iron(III) oxide.

Explain why attaching copper to iron does not provide sacrificial protection.

Need a hint for Question 3?

A sacrificial metal must oxidise more readily than iron.

Check Question 3

Copper is less reactive than iron, so it does not oxidise preferentially to protect the iron.

Use Lesson 5 in your worksheet for written practice. Your teacher will discuss those answers in class.