AQA · Chemistry · 8462
GCSE Chemistry (AQA): Corrosion
Topic 10 — Using Resources. Generated from the caption track of Cognito's lesson video "GCSE Chemistry - What is Corrosion and How to Stop it (2026/27 exams)"; each card deep-links to the moment in the video it came from. Lesson 10.03 of Cognito's AQA GCSE Chemistry (Triple) course (Higher tier), filed under AQA Chemistry 8462. Teaching by Cognito — https://cognitoedu.org/coursesubtopic/c2-gcse-aqa-h-t_10.03.
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How does sacrificial protection stop iron rusting?
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A more reactive metal such as zinc or aluminium is attached, and it is oxidised instead of the iron.
What is galvanising?
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Coating an iron object in a layer of zinc, which acts as both a barrier and sacrificial protection.
Why can a whole block of iron eventually corrode away, not just its surface?
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The rust that forms flakes off, exposing fresh metal underneath which then rusts in turn.
Why is rusting classed as a redox reaction?
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Iron is oxidised (loses electrons) while oxygen is reduced (gains electrons) in the same reaction.
When iron rusts, each iron atom loses ? electrons to form an Fe³⁺ ion.
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three
What is the chemical name for rust?
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Hydrated iron(III) oxide.
Why does aluminium not corrode all the way through?
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The oxidised surface atoms form a layer of aluminium oxide that protects the metal underneath from the environment.
Why does galvanised iron still resist rusting after the zinc layer is scratched?
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Zinc is more reactive than iron, so it is oxidised in preference to the exposed iron.
What is corrosion?
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The process by which metals are slowly broken down by reacting with substances in their environment.
How do barrier methods prevent iron from rusting?
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They stop oxygen and water from ever touching the iron surface.
In the rusting experiment, why is the boiled water covered with a layer of oil?
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It stops oxygen from the air dissolving back into the water, so the nail meets water but no oxygen.
In the rusting test-tube experiment, why is calcium chloride used?
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It removes water vapour from the air, so the nail is exposed to oxygen but no water.
Which two substances must be present for iron to rust?
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Oxygen and water.
Which barrier method of rust prevention suits moving parts such as a bike chain?
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Oiling or greasing.
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