Background

Corrosion is a redox reaction in which a free metal is oxidized, or “corroded,’ by some oxidizing agent. In nature, the oxidizing agent is frequently atmospheric oxygen dissolved in water. Perhaps the most familiar example of corrosion is the rusting of iron. In this reaction, free iron, Fe, is oxidized to Fe²⁺ and Fe³⁺ ions. In the reduction half-reaction, oxygen O₂ reacts with water to form OH^- ions.

The rusting of iron usually is considered to be a destructive change, and considerable time and money are expended to prevent it. One method, which you will observe in this experiment, makes use of a “sacrificial“ metal. When iron is placed in contact with a more active metal (one that is more easily oxidized), the more active metal will be corroded instead of the iron. Metals situated above iron (Fe) on the Activity Series can function as sacrificial metals. 

Materials

• Seven iron finishing nails, one is bent (this has been done for you)
• Copper wire
• Magnesium ribbon
• Fine sandpaper
• Plastic wrap
• Paper plate
• Water
• Erlenmeyer flask
• Table salt
• Petroleum jelly
• Q-tip
• Scoopula
• Paper towels
• Activity Series Reference Table

Safety

• Always wear safety goggles when handling chemicals in the lab.
• Wash your hands thoroughly before leaving the lab.
• Follow the teacher’s instructions for cleanup of materials and disposal of chemicals.
• Wear gloves or use tweezers to safely handle rusty nails.

Discussion Prompts

In your lab group, work together to discuss and answer the following questions:

1. The purpose of this lab is to see how nails will react (corrode or not corrode) in varied environments. Discuss and record how the use of galvanized nails will affect some of those environments; how these nails can affect the purpose of the lab?
2. The background information states that you will observe the use of a sacrificial metal. The two metals that will be used to coat the iron nails are copper and magnesium. Discuss and record which of the two metals should rust when brought together; one iron nail will be coated with copper; the other will be coated with magnesium. Justify your answer based on your research of sacrificial metals and Activity Series Reference Table.
   
   What are some possible examples where the use of a sacrificial metal is important?
   
3. Go to the data table. Read the description of how the nails will be manipulated. This corresponds to the procedures. In your group, use the discussion prompts to predict what will happen to the nails. Record your discussions about what you think will happen to the various nails. Make your predictions, “RUST” OR “NO RUST”; be sure to justify your answers. Your explanation can reference the Activity Series, the presence of oxygen, any preventative measures, etc. Complete these predictions in the data table below.
4. The following discussion prompts are related to a specific step in the lab procedures (below):
   1. Procedure 2: Why do you think we’re using sandpaper on the nails?
   2. Procedure 3: What is the purpose of the wet paper towel? What does it represent?
   3. Procedures 5 and 6: How can the Activity Series help you with this question: Which one of the two would be considered the sacrificial metal? 
   4. Procedure 7: How can coating a metal with something help/prevent the corrosion process?
   5. Procedure 8: What does adding salt do to the corrosion process? How would electrolytic properties play a role in the metal rusting? How would this affect the transfer of electrons?
   6. Procedures 9, 10 and 11: What’s the difference between nail #6 and nail #7?

Procedures

1. Label the bottom of your paper plate with the names of your group members.
2. Use the sandpaper to polish seven nails. Wipe them clean with a paper towel.
3. Place two wet paper towels on the dish (use a pipette to wet paper towels).
4. Nail 1: bend into a U shape (This has been done for you.)
5. Nail 2: wrap one end with copper wire.
6. Nail 3: wrap one end with a strip of magnesium.
7. Nail 4: cover the entire nail with a thin coat of petroleum jelly.
8. Nail 5: moisten with water and sprinkle with table salt.
9. Nail 6: leave untreated.
10. Nail 7: leave untreated.
11. Place nails 1-6 on the wet paper towel. Make sure the nails do not touch. Cover them with a piece of plastic wrap. Place Nail 7 (the control nail) on top of the plastic wrap. 
12. Predict whether the iron nail will or will not corrode/rust.
13. Observations will occur in several days.

Data Table

Complete the data table below. Be sure to justify your answer when predicting whether you think your nail will rust or not. Your nails will be left out several days at which point we will make observations. Only predictions should be recorded on day 1. The observations will continue in a week. 

Analysis Questions

1. As stated in the background information, iron metal, Fe⁰, is oxidized to Fe²⁺ and Fe³⁺ ions. Write the half-oxidation reactions for each of the metal ions formed. 
2. Ionic compounds are considered electrolytes, a solution in which electrons are easily flowing. How does this knowledge help you predict what will happen to the nail that’s been coated in salt that will be contained in a moist environment?
3. What do you expect to happen at the bent nail? Using your prior knowledge of rates of reactions, how does the “bend” act as a catalyst? Explain.
4. Why would you buy galvanized nails? Would you need these on work done on the interior or exterior of a home? Explain.

Error

Were there any unexpected outcomes on the surface of the nails?  If so, explain why this may have happened.

Post Lab Observations/Questions                       

These will be answered after you have seen the results above, in several days.

*Record the Date:

1. Complete the observation portion of the lab. Describe, in detail, what happened to each nail. Write the word ‘nothing’ if nothing happened.
2. Review your predictions and the results. Using your knowledge of REDOX reactions and the Activity Series, explain any of the predictions that were incorrect. 
3. Using your knowledge of sacrificial metals based on the reactivity of metals, explain what happened to:
   1. iron coated with copper
   2. iron coated with magnesium

Conclusion

Based on what you have learned from this lab, how did the properties of the ocean increase the damage caused to cars/buildings/transportation/bridges and electrical systems after a damaging hurricane, such as Superstorm Sandy? Is there anything that could have been done to prevent the damage? What changes have been made to prepare in the event another hurricane occurs?

Advancing Questions (optional)

1. When a ship sinks to the bottom of the ocean, the ship and everything on it is exposed to the harsh elements of the sea. The shipwreck slowly starts to fall apart. Shipwrecks of Spanish galleons are no different. Many of the Spanish galleons contained different types of coins. Silver coins discovered on shipwrecks look like they might be just junk, as they are often black and corroded. However, gold coins still retain their gold finish. Why would a gold coin withstand the elements of the sea better than a silver coin?
2. In the environmentally sensitive coastal waters of Alaska lies The Trans-Alaska Pipeline System (TAPS) which includes the trans-Alaska crude-oil pipeline, 11 pump stations, several hundred miles of feeder pipelines, and the Valdez Marine Terminal. TAPS is one of the world's largest pipeline systems that is facing corrosion, threatening its structural integrity and forcing an expensive and unprecedented crash program of repairs. More information is available at  Parts of Alaska Pipeline Face Corrosion Threat. Based on what you’ve learned today about corrosion, what do you suggest can be done to control/prevent the corrosion of this very important structure?
3. Explain how a passive layer develops on steel. 
4. Why do some companies choose to passivate more frequently than others?