In Earth's atmosphere the air is made up of many different gases. The most common are nitrogen (78%), oxygen (21%), other gases (<1%), and water vapor in varying amounts. Some of  the other gases that have a big effect are carbon dioxide and sulfur dioxide that come from burning of fossil fuels. These gases in the air can and often do combine chemically with metals in Earth such as iron, aluminum, copper, tin, silver and gold to form new compounds that look much different than their parent material. In the chemical reaction with iron nails the iron combines with the oxygen gas and the water vapor to form iron oxides which is also called rust. Sulfur dioxide can combine with water vapor to form acid rain, which has become a worldwide problem.

Silver plates and other silver objects can react with the oxygen in the air to form tarnish. Other chemical compounds are used to remove tarnish and help to restore silver back to its original shiny state. Corrosion control is big business.

Now it's time for you to try and oxidize a penny!

Materials:

• One penny
• Container (e.g. beaker or glass)
• Paper towel
• Graduated cylinder
• Water
• Vinegar
• Watch, clock, or stopwatch

Procedure:

1. Place the penny into the container.
2. Measure 50 ml. of water using a graduated cylinder.
3. Pour the water over the penny.
4. Leave penny immersed in water for 15 minutes
5. Remove the penny from the water and place on paper towel (do not dry off!)
6. Leave the penny to dry for at least 12 hours.
7. Place the penny back into the container.
8. Measure 50 ml. of vinegar using a graduated cylinder.
9. Pour vinegar over the penny and leave immersed for at least 25 minutes.
10. Observe the penny and compare observations based on time while it is under the vinegar.
11. Remove the penny from the vinegar and carefully dry off using paper towel.

Safety concerns: Be sure to follow all glassware, and chemical safety rules that are specified by your teacher in all general laboratory experiences. As with all science lab activities, the most important safety rule is to follow all teacher directions.

Anaylsis:

1. What changes occurred to the penny while it was under the water at the beginning?
2. How did the penny change while it was drying?
3. Why do you think that water was used in this experiment?
4. What changes did you observe while the penny was under the vinegar?
   • How long did it take to see changes to the penny while it was under the vinegar?
5. How did the penny you dried off at the end of the second part of the experiment compare to how it looked when you covered it with vinegar?
6. What purpose did the vinegar serve in the experiment?