What if there was a chemical reaction that:

1
What if there was a chemical reaction that

• Turned vehicles and buildings into dust
• Caused billions of dollars worth of damage per
  year
• Was virtually unstoppable
• Had the potential to destroy an entire planets
  atmosphere

2
Rust

• The Silent Killer

3
Why does rust happen?

• Iron, like most metals, is a strong reducing
  agent
• Earths atmosphere is 21 O2, which is a powerful
  oxidizing agent
• Galvanic cells are easy to set up, and can be as
  simple as a drop of water

4
The Rust Galvanic Cell
Oxidation Fe(s) ? Fe2 2 e-
Reduction O2(g) 2H2O 4e- ? 4 OH-
O2(g)
2 H2O(l)
Fe(s)
5
The Rust Galvanic Cell
Oxidation Fe(s) ? Fe2 2 e-
Reduction O2(g) 2H2O 4e- ? 4 OH-
O2(g)
Particle
2 H2O(l)
Fe(s)
6
The Rust Galvanic Cell
Oxidation Fe(s) ? Fe2 2 e-
Reduction O2(g) 2H2O 4e- ? 4 OH-
2 Fe(s) O2(g) 2H2O ? 2 Fe2 4 OH-
Particle
4 OH-
Fe2
Fe(s)
7
The Rust Galvanic Cell
Particle
4 OH-
2 Fe2
Fe(s)
8
The Rust Galvanic Cell
2 Fe2 4 OH- ? 2Fe(OH)2
Particle
2 Fe(OH)2
Fe(s)
9
The Rust Galvanic Cell
4 Fe(OH)2 O2(g) 2 H2O(l) ? 4 Fe(OH)3
O2(g)
Particle
4 Fe(OH)2
2 H2O(l)
Fe(s)
10
The Rust Galvanic Cell
4 Fe(OH)2 O2(g) 2 H2O(l) ? 4 Fe(OH)3
4 OH-
Particle
4 Fe(OH)2
Fe(s)
11
The Rust Galvanic Cell
4 Fe(OH)2 O2(g) 2 H2O(l) ? 4 Fe(OH)3
Particle
4 Fe(OH)3
Fe(s)
12
The Rust Galvanic Cell
4 Fe(OH)2 O2(g) 2 H2O(l) ? 4 Fe(OH)3
Fe(OH)3 ? Fe2O33 H2O
4 Fe2O3 3 H2O
Fe(s)
13
Questions

• How did the water become an electrolyte?
• What was the anode?
• What was the cathode?
• Would this happen for other metals? Which ones?
  How would it be different?
• Corrosion costs billions of dollars a year in
  damage as boats, cars, trains, building, etc. all
  gradually turn to dust. What can we do to
  prevent rusting from causing so much damage?

14
Rust Prevention Protective layer

• Adding a protective layer of paint, plastic, or
  glass prevents the iron from coming in contact
  with the electrolyte
• What happens if the protective layer develops a
  scratch?

15
Rust Prevention Galvanizing

• If you coat iron in a thin layer of zinc, it is
  called galvanization. The layer both protects
  the iron and will act as the anode if a scratch
  develops
• What happens when all the zinc is oxidized?

Fe2O3 3 Zn ? 3 ZnO 2 Fe
16
Rust Prevention Sacrificial Anode

• Some ships and gas pipelines are protected by
  putting a block of zinc, aluminum, or magnesium
  on them. The more reactive metal is oxidized and
  the iron stays intact.
• Who pays to replace the sacrificial anode every
  year?

17
Rust on Mars

• The surface of mars is completely covered in
  rust. Scientists think that Mars might once have
  had an atmosphere like earths, but all of that
  oxygen is now tied up in Fe2O3.
• Question why hasnt this happened on Earth?

18
Practice Questions

• In 2000, Transport Canada recalled thousands of
  cars with corroded engine mounts in Nova Scotia,
  New Brunswick, and PEI. Why was corrosion such a
  problem in these provinces?
• A small scratch in a car door can quickly develop
  into a major rust spot. Why does this happen?
• Does acid rain promote or prevent corrosion?
  Explain?