CAIE IGCSE Chemistry Rusting and Corrosion Prevention

Practise identifying the conditions for rusting and explaining barrier protection, galvanising and sacrificial protection through contact and reactivity.

Exam points

state that iron requires both oxygen and water to form hydrated iron(III) oxide rust
explain paint, oil or intact coating as barriers that exclude water and oxygen
explain sacrificial protection using a more reactive metal that oxidises instead of iron

Covered syllabus points

9.5.1—Conditions required for the rusting of 9.5.2—Some common barrier methods 9.5.3—Barrier methods prevent rusting by 9.5.4—Use of zinc in galvanising as an 9.5.5—Sacrificial protection in terms of the

[Maximum number: 5]

This question is about iron.

(a)

Iron forms rust.

Rusting is prevented by coating iron with zinc.

[ 5 ]

(i)

Name the substances that react with iron to form rust.

[ 1 ]

(ii)

Name the process in which zinc is used to coat iron to prevent rusting.

[ 1 ]

(iii)

Explain how the coating of zinc prevents rusting if the zinc is not scratched.

[ 1 ]

(iv)

When zinc is scratched the iron becomes exposed.

Explain how the zinc continues to prevent rusting.

[ 2 ]

[Maximum number: 5]

Iron is manufactured in a blast furnace.

(a)

Preventing the rusting of steel is important.

State the chemical name of rust.

[ 1 ]

(b)

Steel can be coated with zinc to prevent rusting. This provides both a barrier method and sacrificial protection.

[ 4 ]

(i)

State the term used for coating steel with zinc.

[ 1 ]

(ii)

Describe another barrier method for preventing rusting.

[ 1 ]

(iii)

Explain how zinc provides sacrificial protection.

[ 2 ]

[Maximum number: 4]

(a)

The metal iron and the alloy steel are commonly used materials. A problem with them is that they rust.

[ 4 ]

(i)

How does painting iron and steel prevent rusting?

[ 1 ]

(ii)

Magnesium blocks can be attached to the bottom of steel boats.

Explain how the magnesium blocks prevent the whole of the bottom of the boat from rusting.

[ 2 ]

(iii)

Replacing the magnesium blocks with copper blocks does not prevent rusting.

Explain why the copper blocks do not prevent rusting.
[Total: 10]

[ 1 ]

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Covered syllabus points

9.5 Corrosion of metals question 1

Question (a)

Question (i)

Question (ii)

Question (iii)

Question (iv)

9.5 Corrosion of metals question 2

Question (a)

Question (b)

Question (i)

Question (ii)

Question (iii)

9.5 Corrosion of metals question 3

Question (a)

Question (i)

Question (ii)

Question (iii)