4/26/2010
Learning Objectives
Rusting
Rusting is everywhere.
• Describe the conditions in which rusting
occurs.
• Describe the methods of rust prevention.
What is Rust?
• Rust is a reddish-brown solid substance
that forms on the surface of a metal.
• Chemical name of rust: hydrated iron (III)
oxide
Learning through investigation
Woon Kit conducted an experiment to
investigate the conditions needed for rusting. He
placed iron nails in 3 test tubes with different
substances and left them in the test tubes for 1
week.
A
B
C
Test tube A: Boiled water
Test tube B: Anhydrous Calcium Chloride (this
absorbs moisture in the air)
Test tube C: Water
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• After 1 week, Woon Kit observed the iron
nails.
• Refer to the 3 samples of iron nails (A, B, C).
Test tube
A
B
Appearance
of iron nails
Iron
Iron nail
nail
remains
remains shiny
shiny
Reddishbrown solid
formed on
the iron nail
Did rusting
occur?
No
Yes
No
C
• In which test tubes did rusting occur?
Test tube C
Word equation for rusting:
• What substances are necessary for
rusting to occur?
Water and Air are necessary for rusting
to occur, specifically iron reacts with
the oxygen in the air.
Iron + oxygen + water  hydrated iron (III) oxide
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Rust Prevention
3 general methods of rust prevention:
The equation for rusting is
4Fe + 3O2 + 2xH2O
2Fe2O3.xH2O
1. using a protective layer
2. Using a sacrificial metal
3. Using alloys
All these methods create a barrier around
the metal, thus, keeping the metal away
from water and oxygen.
WHY?
Food cans are examples of iron plated
with a thin layer of tin in order to prevent
rusting. However, it is noticed that when
tin plate is scratched or broken, rusting
occurs even more rapidly.
Using your knowledge of the reactivity
series of metals, explain why this is so.
ANSWER
Tin is less reactive than iron. When both
tin and iron are exposed to air and water,
iron will more readily react with oxygen to
form rust, as compared to tin corroding in
air.
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