Metals 8 - Self Check Quiz

Which metal should be used in the sacrificial protection of the hull of a boat made from iron?

• Aluminium

• Calcium

• Copper

• Silver

Answer explanation

Should use a metal which is more reactive than iron.

Calcium can react readily with cold water so it is not suitable to be used.

Which process for the prevention of the rusting of iron is based on a different principle to the others?

• Galvanizing

• Greasing

• Painting

• Wrap in plastic

Answer explanation

Galvansing gives 2 fold protection: a protective layer and also sacrificial protection

Each beaker contains two strips of metal fastened together and immersed in hydrochloric acid. All the strips are of the same size.

    After 5 minutes, which beaker contains the least amount of zinc ions?

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Answer explanation

Magnesium is more reactive than zinc. So it will oxidised first in favor of zinc.

Which diagram correctly illustrates the conditions necessary for the rusting of iron and also the metal that can be used to prevent rusting by sacrificial protection ?

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Answer explanation

The conditions necessary for the rusting of iron are water and oxygen.

The metal used for sacrificial protection is more reactive than iron.

Iron (II) ions in aqueous solution produce a blue colouration with aqueous potassium hexacyanoferrate (III ). A student investigated the corrosion of iron when in contact with several metals. The experiments he set up are shown in the diagram.

In which test-tubes would a blue colour not appear around the iron nail after some time?

• A

• B

• C

• D

Answer explanation

Magnesium is more reactive than iron. So it will corrode first in favour of iron.

The chromium in the stainless steel reacts with oxygen in the air to form chromium oxide. The chromium oxide forms a layer on the surface of the stainless steel. This layer stops the iron  in the stainless steel from rusting.

The formula for chromium oxide is Cr₂O₃.

What is the formula for the chromium ion?

Suggest how the layer of chromium oxide stops the iron in the stainless steel from rusting.                                                                                                                  

Answer explanation

Key terms: "protective layer", "prevents water and oxygen from contacting iron"

Door handles and trims on some cars are made from iron coated with chromium. Chromium is a more reactive metal than iron.

If the chromium coating is scratched, would you expect the iron underneath to rust? Explain your answer.                                                                                                 

Answer explanation

Key terms: more reactive, oxidises and corrodes first in favour of iron

Suggest a method that could be used to apply the chromium coating to the iron.