Gold and Silver Pennies Fun Chemistry Project

All you need are a couple of common chemicals to turn your normal copper-colored pennies (or other mainly-copper object) from copper to silver and then to gold. No, the coins won't really be silver or gold. The actual metal involved is zinc. This project is easy to do. While I don't recommend it for very young kids, I'd consider it appropriate for kids ages third grade and older, with adult supervision.

Materials Needed for this Project

• clean pennies
• zinc metal (preferably powder)
• sodium hydroxide or sodium hydroxide solution
• tweezers or tongs
• container of water
• source of heat/flame

Note: Supposedly you can substitute galvanized nails for the zinc and Drano™ for the sodium hydroxide, but I was unable to get this project to work using nails and drain cleaner.

How to Make Silver Pennies

1. Pour a spoonful of zinc (1-2 grams) into a small beaker or evaporating dish containing water.
2. Add a small quantity of sodium hydroxide.
3. Alternatively, you could add zinc to a 3M NaOH solution.
4. Heat the mixture to near-boiling, then remove it from heat.
5. Add clean pennies to the solution, spacing them so that they are not touching each other.
6. Wait 5-10 minutes for them to turn silver, then use tongs to remove the pennies from the solution.
7. Rinse the pennies in water, then set them on a towel to dry.
8. You can examine the pennies once you have rinsed them.

This chemical reaction plates the copper in the penny with zinc. This is called galvanization. The zinc reacts with the hot sodium hydroxide solution to form soluble sodium zincate, Na₂ZnO₂, which is converted to metallic zinc when it touches the surface of the penny.

How to Make the Silver Pennies turn Gold

1. Grasp a silver penny with tongs.
2. Gently heat the penny in the outer (cool) part of a burner flame or with a lighter or candle (or even set it on a hotplate).
3. Remove the penny from heat as soon as it changes color.
4. Rinse the gold penny under water to cool it.

Heating the penny fuses the zinc and copper to form an alloy called brass. Brass is a homogeneous metal that varies from 60-82% Cu and from 18-40% Zn. Brass has a relatively low melting point, so the coating can be destroyed by heating the penny for too long.

Safety Information

Please use proper safety precautions. Sodium hydroxide is caustic. I recommend conducting this project under a fume hood or outdoors. Wear gloves and protective eyewear to prevent getting splashed by the sodium hydroxide solution.

source : http://chemistry.about.com