Pot of Gold At The End of the Rainbow

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Here is a possible reason why we can't find that pot of gold! It's hidden! Check out the experiment below that changes copper pennies into silver...and then to gold! (Well, brass, technically...but who's keeping track?)

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Materials:Materials for "Pot of Gold at the End of the Rainbow" Experiment046.JPG

  • Pennies
  • Zinc metal (preferably powder)
  • Sodium hydroxide solution
  • tweezers/tongs
  • container of water
  • source of heat/flame



Step 1 - turning copper pennies to silver

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

The 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.

Step 2 - turning silver pennies to gold, well, er...brass...

  1. Grasp a silver penny with tongs.
  2. Gently heat the penny on the hotplate.
  3. Remove the penny from heat as soon as it changes color.heat
  4. Rinse the gold penny under water to cool it.

How does it work?

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. We recommend using a fume hood or outdoors. Wear protective eye wear and gloves to prevent getting splashed by the sodium hydroxide solution.colors