Two steel bicycle stands are kept outdoors. One is protected by paint and the other is galvanised. Both coatings have been scratched, exposing the steel. A caretaker can repair only one coating immediately.
Why should the painted coating be repaired first?
Zinc protects only as a barrier, but paint still protects the exposed steel sacrificially.
Scratched paint corrodes in air and water, but scratched zinc does not corrode at all.
Paint lets air reach the scratch, but zinc still keeps air away from the exposed steel.
Paint protects only as a barrier, but zinc still protects the exposed steel sacrificially.
118 exam-style questions on AQA GCSE Chemistry 10.3 Using materials, covering 10.3.1 Corrosion and its prevention, 10.3.2 Alloys as useful materials, and 10.3.3 Ceramics, polymers and composites. Each one has a worked solution and a mark scheme showing where the marks go.