Corrosion

Question 1

What is corrosion?

Answer 1

• The proces by which metals are slowly broken down by reacting with substances in their environment

Question 2

Rusting of metal with equation

Answer 2

• Iron reacts with oxygen and rusts
• Iron + oxygen + water = hydrated iron oxide (rust)

Question 3

How to investigate conditions required for rusting

Answer 3

• Test tube 1 - water but no oxygen: done by boiling water to remove oxygen and layer of oil on top to prevent new oxygen
• Test tube 2 - oxygen but not water: contains calcium chloride which removes water vapour from air
• Test tube 3 - contains air (oxygen) and water
• Only iron in test tube 3 rusts as it contains required reactants: oxygen and water

Question 4

What part of the metal corrodes in iron and aluminium?

Answer 4

• Only the surface corrodes as only the surface is exposed to the air
• Iron: rust flakes off and reveals new layer of metal beneath. If left long enough, whole metal with rust
• Aluminium: corrodes to form aluminium oxide, which acts as a protective layer and so only surface corrodes

Question 5

What are the different types of methods for preventing rust?

Answer 5

• Barrier methods - prevent oxygen and water from touching iron
• Sacrificial methods

Question 6

Barrier methods for preventing rust

Answer 6

• Paint it: works well with big pieces
• Oil or grease it: necessary if object has moving parts
• Electroplating: using electrolysis to cover iron with a thin layer of another metal

Question 7

Sacrificial methods for preventing rust

Answer 7

• Adding a more reactive metal to the iron
• Therefore, if exposed to oxygen, the more reactive metal with react and the iron won’t rust

Question 8

Method that uses both barrier and sacrifical to prevent rust

Answer 8

• Galvanising: coats iron in a layer of zinc
• Barrier as it is stopping the oxygen and water touching the iron
• Sacrificial as zinc is more reactive than iron