An outdoor steel winch has a chain protected by grease and a support coated with zinc. The grease wears off the chain and the zinc coating is scratched, exposing steel on both parts. Before the winch is used again, the chain is re-greased but the zinc coating is not repaired. The winch is then exposed to air and rainwater.
What happens?
Only the support is protected: zinc is sacrificial, but grease does not form a barrier to air and water
Both steel parts rust: each method fails once its original protective layer has been damaged
Only the chain is protected: the new grease is a barrier, but the scratched zinc cannot protect the support
Both steel parts are protected: grease forms a new barrier, while zinc corrodes in preference to the steel support
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.