7: Corrosion

Question 1

When does corrosion happen?

Answer 1

When metals react with substances in the surroundings, such as air and water

Question 2

Why does Aluminium not corrode easily despite it being a reactive metal?

Answer 2

It has a very thin natural layer of aluminium oxide. This layer is tightly bound to the metal and does not flake off. It stops air and water getting to the metal itself

Question 3

What happens to iron?

Answer 3

It rusts. Iron is oxidised when it rusts. It is not protected by a layer of its oxide as iron oxide flakes easily, exposing fresh metal underneath. It needs both air and water to rust.
A layer of paint will prevent rusting

Question 4

What is the role of salt in rusting?

Answer 4

It speeds up rusting

Question 5

What is rust?

Answer 5

Iron is oxidised in hydrated iron(III) oxide when it reacts with oxygen and water:
iron + oxygen + water = hydrated iron(III) oxide
The product creates the orange-brown colour

Question 6

Iron and Aluminium: similarities

Answer 6

malleable

good electrical conductors

Question 7

Iron and Aluminium: differences

Answer 7

• iron corrodes easily whereas aluminium does not
• iron is more dense than aluminium
• iron is magnetic whereas aluminium is not