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Rust differs from copper patina in that the rust layer:
AFully seals the metal
BConducts electricity better
CConverts back into iron
DDoes not protect the metal
Answer & Solution
Correct answer: D. Does not protect the metal
1. Further reaction of the iron(II) product in humid air produces an iron(III) oxide hydrate known as rust.
2. A protective product would seal the surface and stop the process.
3. Unlike the patina on copper, the formation of rust does not create a protective layer.
4. So corrosion of the iron continues as the rust flakes off and exposes fresh iron to the atmosphere.
5. That flaking is why rusting is progressive rather than self-limiting.
_Source: OpenStax Chemistry 2e (CC BY 4.0), Ch 17 'Electrochemistry', sections 17.1-17.7_
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