Corrosion
• Many things are made of iron. However, iron has one major
drawback – it goes rusty.
iron + water + oxygen  rust
• Rust is the product of the corrosion
of iron.
• Other examples include silver
tarnish and the green film that
forms on copper or brass objects.
Ways to stop corrosion
There are many ways to stop corrosion from occurring:
•
PAINTING: so metal is not exposed to air.
•
COATING WITH OIL, GREASE or TAR: for metal surfaces
which can not be painted.
•
COATING WITH PLASTIC: so metal is not exposed.
•
COATING WITH METAL: eg. Galvanising.
Coating iron with a layer of zinc slows
corrosion because the zinc is more
reactive than iron.
Rusting can be useful!
RUSTING CAN BE
USEFUL!
Hand warmers
worn by skiers are
made of a powder
of iron, salt and
sawdust. When
shaken vigorously,
iron rusts,
producing heat.
What causes rusting?
Read through the practical report on ‘Rusting’ and then answer
the questions which follow.
What causes rusting?
QUESTIONS:
1. Write an aim and list the materials required for the
experiment.
AIM: To investigate what causes rusting.
MATERIALS:
•
•
•
•
•
•
5 x test tubes
Test tube rack
5 x pieces of iron wool
Tap water
Oil
Salt water
•
•
•
•
•
Salt
10 ml measuring cylinder
Silica gel / calcium chloride
Spatula
Rubber stopper
What causes rusting?
QUESTIONS:
2. Record the results obtained in the ‘results’ section of this
report.
Test tube
Conditions
Observations
What causes rusting?
QUESTIONS:
2. Record the results obtained in the ‘results’ section of this
report.
Test tube
Conditions
Observations
1
Air & Water
Iron wool rusts. Some falls to
bottom of test tube.
What causes rusting?
QUESTIONS:
2. Record the results obtained in the ‘results’ section of this
report.
Test tube
Conditions
Observations
1
Air & Water
Iron wool rusts. Some falls to
bottom of test tube.
2
Air & Calcium Chloride
No rust
What causes rusting?
QUESTIONS:
2. Record the results obtained in the ‘results’ section of this
report.
Test tube
Conditions
Observations
1
Air & Water
Iron wool rusts. Some falls to
bottom of test tube.
2
Air & Calcium Chloride
No rust
3
Water & Oil
Small amounts of rust
What causes rusting?
QUESTIONS:
2. Record the results obtained in the ‘results’ section of this
report.
Test tube
Conditions
Observations
1
Air & Water
Iron wool rusts. Some falls to
bottom of test tube.
2
Air & Calcium Chloride
No rust
3
Water & Oil
Small amounts of rust
4
Air & Salt
No rust
What causes rusting?
QUESTIONS:
2. Record the results obtained in the ‘results’ section of this
report.
Test tube
Conditions
Observations
1
Air & Water
Iron wool rusts. Some falls to
bottom of test tube.
2
Air & Calcium Chloride
No rust
3
Water & Oil
Small amounts of rust
4
Air & Salt
No rust
5
Air, Salt & Water
Iron wool rusts. Some falls
apart and collects at bottom.
What causes rusting?
QUESTIONS:
3. In which test tubes did the iron wool rust quickly? Why?
Test tubes 1 & 5 because they have iron, air & water together.
4. In which test tubes did the iron wool not rust? Why?
Test tubes 2, 3 & 4 because they either air or water was
missing.
What causes rusting?
CONCLUSIONS:
1. What conditions are necessary for the iron wool to rust?
Iron needs air and water together for rusting. Salt speeds up
the rusting process.
2. How could you stop the iron from going rusty?
You would exclude water or air or both. This can be done by
covering the metal with paint, oil, plastic or another metal.
You could also keep the air dry by using silica gel (calcium
chloride).
What causes rusting?
ACTIVITY:
1. What is meant by the following terms:
CORROSION:
Reaction of metals with oxygen and water
in which they dissolve away.
RUSTING:
The corrosion of iron.
GALVANISED:
Iron covered with zinc.
2. What are the three reactants needed for corrosion?
Iron, water & air.
What causes rusting?
ACTIVITY:
3. Some clothes stands are coated with a white plastic. When
this plastic ages and cracks there is rust. Why is this?
Cracks in the plastic allow air and water to react with the iron
inside.
Rusting: Fresh v’s Salt Water
AIM: To determine which reaction is faster – rusting in fresh
water or rusting in salt water.
METHOD:
1. Pour some fresh water into a petri dish 1 and some salt
water into petri dish 2.
2. Place a small piece of steel wool (the same size) into both
petri dishes.
3. Cover the steel wool by placing a beaker upside down.
4. Mark the water level on the beaker.
5. Observe what occurs over several days.
Rusting: Fresh v’s Salt Water
RESULTS:
Condition
Fresh
water
Salt water
Day 1
Day 2
Day 3
Day 4
Day 5