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IGCSE · Practice questions · Rusting and its prevention

Stop the rust.

Six original Cambridge-style questions on rusting: its conditions, the classic experiment and the methods used to prevent it.

Original questions All questions on this page are original work, written in the Cambridge IGCSE style. They are not from past papers. They test the same concepts and skills the syllabus rewards.
Keep these straight

Water and oxygen, both.

01
Recall
[2 marks]

State the two conditions needed for iron to rust, and give the chemical name of rust.

  • Oxygen (air) and water. ✓
  • Hydrated iron(III) oxide. ✓
02
Explain
[3 marks]

Describe an experiment using three iron nails to show that both water and oxygen are needed for rusting.

  • Tube 1: nail in water open to the air; it rusts. ✓
  • Tube 2: nail in boiled water with a layer of oil on top (no oxygen); it does not rust. ✓
  • Tube 3: nail in air dried with anhydrous calcium chloride (no water); it does not rust. ✓
03
Recall
[3 marks]

Suggest a suitable method of rust prevention for (a) a car body, (b) a bicycle chain and (c) a steel dustbin.

  • (a) painting. ✓
  • (b) oiling or greasing. ✓
  • (c) galvanising (coating with zinc). ✓
04
Explain
[2 marks]

Explain how painting prevents rusting, and why a scratched painted surface starts to rust.

  • Paint forms a barrier that keeps water and oxygen away from the iron. ✓
  • When scratched, water and oxygen reach the exposed iron, so it rusts. ✓
05
Explain
[3 marks]

(Extended) Explain, in terms of reactivity and electrons, how blocks of zinc attached to a steel ship's hull prevent the hull rusting.

  • Zinc is more reactive than iron. ✓
  • Zinc loses electrons (is oxidised) more readily than iron, so it corrodes instead of the iron. ✓
  • The iron is protected as long as zinc remains; this is sacrificial protection. ✓
06
Analysis
[2 marks]

(Extended) Suggest why copper blocks could not be used for sacrificial protection of iron.

  • Copper is less reactive than iron. ✓
  • So iron would lose electrons and corrode instead of the copper (rusting would be faster). ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.