MediumChemistryHigh School (9–10)GeneralChemical Reactions › Energy Changes and CorrosionConceptualBoard Exam
Iron pipes are galvanised: they are coated with zinc…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Iron pipes are galvanised: they are coated with zinc. Food cans are coated with tin.
- How does the zinc stop rusting, even when it is scratched?
- Why does a scratched tin can rust faster than a scratched galvanised pipe?
Need a reminder? The key ideaShow
Iron rusts only when both air (oxygen) and water are present; salt speeds it up. Rusting is prevented by painting, oiling, galvanising with zinc, or alloying. Rancidity is the oxidation of fats and oils; antioxidants, airtight packs, cold and nitrogen gas slow it.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. (a) Zinc covers the iron, keeping air and water away. Zinc is also more reactive than iron, so at a scratch the zinc corrodes in place of the iron.
Step 2. (b) Tin is less reactive than iron. At a scratch, the iron corrodes first, so rust starts at once.
Answer: zinc protects by giving itself up; tin only covers the iron.
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