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 planet’s atmosphere

2. Rust The Silent Killer

3. Why does rust happen? Iron, like most metals, is a strong reducing agent Earth’s atmosphere is 21% O 2, 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 Fe (s) 2 H 2 O (l) Particle O 2(g) Oxidation: Fe (s)  Fe 2+ + 2 e - Reduction: O 2(g) + 2H 2 O + 4e -  4 OH -

5. The Rust Galvanic Cell Fe (s) 2 H 2 O (l) Particle O 2(g) Oxidation: Fe (s)  Fe 2+ + 2 e - Reduction: O 2(g) + 2H 2 O + 4e -  4 OH - 2 e - Fe 2+

6. The Rust Galvanic Cell Fe (s) Particle Oxidation: Fe (s)  Fe 2+ + 2 e - Reduction: O 2(g) + 2H 2 O + 4e -  4 OH - Fe 2+ 4 OH- 2 Fe (s) + O 2(g) + 2H 2 O  2 Fe 2+ + 4 OH -

7. The Rust Galvanic Cell Fe (s) Particle 2 Fe 2+ 4 OH-

8. The Rust Galvanic Cell Fe (s) Particle 2 Fe(OH) 2 2 Fe 2+ + 4 OH -  2Fe(OH) 2

9. The Rust Galvanic Cell Fe (s) Particle 4 Fe(OH) 2 4 e - O 2(g) 2 H 2 O (l) 4 Fe(OH) 2 + O 2(g) + 2 H 2 O (l)  4 Fe(OH) 3

10. The Rust Galvanic Cell Fe (s) Particle 4 Fe(OH) 2 4 Fe(OH) 2 + O 2(g) + 2 H 2 O (l)  4 Fe(OH) 3 4 OH -

11. The Rust Galvanic Cell Fe (s) Particle 4 Fe(OH) 3 4 Fe(OH) 2 + O 2(g) + 2 H 2 O (l)  4 Fe(OH) 3

12. The Rust Galvanic Cell Fe (s) 4 Fe 2 O 3 · 3 H 2 O 4 Fe(OH) 2 + O 2(g) + 2 H 2 O (l)  4 Fe(OH) 3 Fe(OH) 3  Fe 2 O 3 ·3 H 2 O

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? Fe 2 O 3 + 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 earth’s, but all of that oxygen is now tied up in Fe 2 O 3. Question: why hasn’t 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?