O LevelChemistryCambridgeExam Questions9. Metals9.5 Corrosion of Metals

Corrosion of Metals (Cambridge O Level Chemistry)

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9.5 Corrosion of Metals

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9.5 Corrosion of Metals

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1a2 marks

Many compounds have important uses.

The table compares the reactions of four metals with steam.

metal reaction with steam
copper does not react
magnesium reacts rapidly
sodium reacts explosively
zinc reacts slowly when warmed

Put the four metals in order of their reactivity.

Put the least reactive metal first.

q3b_0620-s20-qp-32_cie-igcse-chemistry

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1b2 marks

Rust contains hydrated iron(III) oxide.


Describe and explain one method of preventing iron from rusting.

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1a4 marks

Rusting of steel can be prevented by coating the steel with a layer of zinc.

Explain, in terms of electron transfer, why steel does not rust even if the layer of zinc is scratched so that the steel is exposed to air and water.

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1b6 marks

When a sample of steel is added to dilute hydrochloric acid, an aqueous solution of iron(II) chloride, FeCl2, is formed.

When a sample of rust is added to dilute hydrochloric acid, an aqueous solution of iron(III) chloride, FeCl3, is formed.

i)
Aqueous sodium hydroxide is added to the solutions of iron(II) chloride and iron(III) chloride.

Complete the table below, showing the observations you would expect to make.

  Iron(II) chloride solution Iron(III) chloride solution
Aqueous
sodium hydroxide		    

[2]

Solutions of iron(II) chloride and iron(III) chloride were added to solutions of potassium iodide and acidified potassium manganate(VII). The results are shown in the table.

  Iron(II) chloride solution Iron(III) chloride solution
Potassium
iodide solution		 No change Solution turns
from colourless
to brown
Acidified potassium
manganate(VII)
solution		 Solution turns
from purple
to colourless		 No change

ii)
What types of substance cause potassium iodide solution to turn from colourless to brown?

[1]

iii)
What types of substance cause acidified potassium manganate(VII) solution to turn from purple to colourless?
[1]
iv)
Which ion in iron(III) chloride solution causes potassium iodide solution to turn from colourless to brown?
[1]
v)
Which ion in iron(II) chloride solution causes acidified potassium manganate(VII) solution to turn from purple to colourless?
[1]

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2a4 marks

Steel is an alloy made from impure iron.

Both iron and steel rust. The formula for rust is Fe2O3.2H2O. It is hydrated iron(III) oxide.

i)
Name the two substances that must be present for rusting to occur.
[2]
ii)
Painting and coating with grease are two methods of preventing iron or steel from rusting. Give two other methods.
[2]

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2b3 marks
i)
Name a reagent that can reduce iron(III) oxide to iron.

[1]

ii)
Write a symbol equation for the reduction of iron(III) oxide, Fe2O3, to iron.

[2]

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2c
Sme Calculator3 marks
i)
Calculate the mass of one mole of Fe2O3.2H2O.
[1]

ii)
Use your answer to (i) to calculate the percentage of iron in rust.
[2]

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2d3 marks

Iron from the blast furnace is impure. Two of the impurities are carbon and silicon. These are removed by blowing oxygen through the molten iron and adding calcium oxide.

 

i)
Explain how the addition of oxygen removes carbon.
[1]
ii)
Explain how the addition of oxygen and calcium oxide removes silicon.
[2]

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1a3 marks

This question is about alloys. 

Brass is an alloy which contains zinc.
 

i)
Name the other metal in brass.
 
[1]
 
ii)
Suggest two reasons why an alloy such as brass is preferred to either of its constituent metals.
 
[2]

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1b5 marks

In an experiment to investigate the rate of rusting of steel, three pieces of steel were used.

One piece of steel was completely coated with copper, one piece completely coated with zinc and the third piece was left uncoated. All three pieces were left exposed to the atmosphere.

i)
Explain why the uncoated piece started to rust.
[1]

ii)
The coating on both of the other two pieces was scratched, exposing the steel.

The piece of steel coated with zinc still did not rust but the copper-coated piece of steel rusted very rapidly.

Explain these observations in terms of the formation of ions and the transfer of electrons.

[4]

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