9.5 Corrosion of Metals (Cambridge (CIE) O Level Chemistry): Flashcards
Exam code: 5070
1/140Still learning
Know0
- FrontRusting of Iron
Rust is chemically known as hydrated ______ oxide.
Was this flashcard helpful?
Cards in this collection (14)
Rust is chemically known as hydrated ______ oxide.
Rust is chemically known as hydrated iron(III) oxide.
Describe the three-test-tube experiment that shows both water and oxygen are needed for rusting.
One tube contains iron in dry air (no water), one contains iron in boiled water under oil (no oxygen), and one contains iron in ordinary water and air.
Only the third tube shows rusting, proving both water and oxygen are needed.
In the rusting experiment, water is boiled before use to remove dissolved ______, ensuring the iron is exposed to water without oxygen.
In the rusting experiment, water is boiled before use to remove dissolved air/oxygen, ensuring the iron is exposed to water without oxygen.
True or False?
In the three-test-tube rusting experiment, the oil layer on top of the boiled water prevents water from evaporating.
False.
The oil layer prevents oxygen from dissolving back into the boiled water, so the iron is exposed to water but not oxygen.
Painting, greasing and plastic coating all prevent rusting by acting as a ______ that keeps water and oxygen away from the iron surface.
Painting, greasing and plastic coating all prevent rusting by acting as a barrier that keeps water and oxygen away from the iron surface.
Explain why a zinc coating on iron continues to protect it even if the zinc layer is scratched.
Zinc is more reactive than iron, so even when scratched, the zinc loses electrons and corrodes before the iron does. This is called sacrificial protection.
Three barrier methods used to prevent rusting are painting, greasing and coating with ______.
Three barrier methods used to prevent rusting are painting, greasing and coating with plastic.
What is sacrificial protection?
Sacrificial protection is a method of preventing rusting by attaching a more reactive metal to the iron, which corrodes preferentially and is sacrificed to protect the iron.
Zinc protects iron by sacrificial protection because zinc is ______ reactive than iron.
Zinc protects iron by sacrificial protection because zinc is more reactive than iron.
Why does zinc protect iron even after the zinc coating is scratched?
Zinc is higher in the reactivity series than iron, so it loses electrons more readily. Even when the zinc is scratched and iron is exposed, the zinc corrodes preferentially, protecting the iron underneath.
Galvanising involves coating iron or steel with a thin layer of ______ to protect it from rusting.
Galvanising involves coating iron or steel with a thin layer of zinc to protect it from rusting.
True or False?
Galvanising protects iron only by forming a physical barrier between the iron and the atmosphere.
False.
Galvanising protects iron in two ways: it forms a physical barrier, and it also provides sacrificial protection because zinc is more reactive than iron.
The zinc half-equation for sacrificial protection shows that zinc ______ electrons to form zinc ions.
The zinc half-equation for sacrificial protection shows that zinc loses electrons to form zinc ions.
Describe two methods by which iron can be galvanised.
Iron can be galvanised by electroplating it with zinc, or by dipping it into molten zinc. Both methods coat the iron with a protective zinc layer.
Sign up to unlock flashcards
or