ChemTalk

Copper crystals in a beautiful pattern

Copper crystals tree pattern

Some people are familiar with the process of growing crystals of copper sulfate, or even copper acetate. However, very few people know that you can make beautiful metallic copper crystals through a simple oxidation-reduction reaction with zinc. This is easily done on a piece of filter paper in a petri-dish.

Procedure for beautiful copper crystals

  1. Prepare a solution of copper sulfate pentahydrate. You won’t need much. I usually dissolve 7.5 grams of copper sulfate in 50ml of distilled water.
  2. Cut a piece of filter paper so it just fits inside a petri dish
  3. Place a dry filter paper into the petri dish
  4. Pour a small amount of copper sulfate solution into the petri dish, soaking the filter paper.
  5. After a few seconds, pour out the solution, so you are left with a wet piece of filter paper.
  6. Place a tiny piece of zinc metal, or a small amount of zinc powder, in the middle of the filter paper.
  7. Wait until the metallic copper forms around the zinc. You should see some within minutes.

Tips and tricks

  • If you don’t get the beautiful tree / fractal pattern like shown in our photo, try soaking the filter paper with more or less copper sulfate
  • Copper sulfate is toxic, keep the solution away from eating and living areas, and use proper PPE (gloves and goggles)
  • Copper sulfate can be purchased at hardware stores as Rooto root killer. It is once of the most useful compounds for chemistry experiments.
  • It’s normal for it to take a little while for all of the CuSO4 to dissolve
  • The copper crystals will be very small, use a magnifying glass to see them better.
  • Give the crystals an hour or two to form.

Explanation of the chemistry

The copper is being reduced from copper (II) ions to elemental copper, by zinc which is possibly the most useful reducing agent you can have. The zinc is oxidized from elemental zinc to the zinc (II) ion. The sulfate ion acts as a spectator ion.

Net ionic reaction: Cu+2 + Zn(s) -> Cu(s) + Zn+2

This reaction occurs spontaneously because zinc is higher than copper in the activity series of metals. You will find memorizing the order of the activity series helpful in mastering chemistry.

Large amounts of elemental copper can be more easily formed from a copper sulfate solution via a different method, which we will explore in a different article. Like gallium, elemental copper is non-toxic.

Additional Experiments

Make copper powder from aluminum foil
Make beautiful tin crystals