It’s easy to grow copper metal crystals using a bit of electrochemistry. These are very pure metal crystals that range in shape from delicate fern-like forms to chunky geometric crystals. Here are three methods. One uses electricity for electrolysis, while the other two rely on the metal activity series for single replacement reactions.
About Copper Sulfate
Each method uses a copper sulfate solution. You can buy copper sulfate already in aqueous solution as an algae treatment for swimming pools and ponds. Just check the label and make certain the only ingredients are copper sulfate (CuSO4) and water. However, a better option, especially if you are growing large crystals, is solid copper sulfate. This is sold either as copper sulfate or as copper sulfate pentahydrate. It consists of blue granules or crystals and is available in home supply stores as a stump remover or root killer. Again, check the label for the ingredients. Copper(II) sulfate pentahydrate is available online, too, mainly for growing crystals.
Grow Delicate Copper Metal Crystals
This first method is the quickest method of growing copper crystals. The resulting crystals are delicate and resemble ferns or Lichtenberg figures.
- Copper sulfate
- Small piece of zinc or iron
- Petri dish or other shallow dish
- Filter paper or coffee filter
Zinc is the metal coating on galvanized nails. Iron is readily available as a pure metal, too. You don’t need a large piece of metal (metals shavings are fine). The premise is that zinc or iron has the same 2+ oxidation state as copper in copper sulfate, but these metals are higher on the metal activity series. So, a single replacement reaction occurs where the zinc or iron enters solution, replacing copper, which precipitates out of solution and crystallizes.
The net ionic reaction is as follows:
Cu2+(aq) + Zn(s) → Zn2+(aq) + Cu(s)
- Place the dry filter paper into the bottom of the dish. If necessary, trim it so it just fits.
- Dissolve copper sulfate in a small amount of water. A good starting point is 7.5 grams of copper sulfate in 50 milliliters of water. You want enough water that it can cover the bottom of your dish and soak the filter paper. Add enough copper sulfate to give a deep blue color. But, you do not need a saturated solution (or you’ll get copper sulfate crystals).
- Pour enough of this solution onto the filter paper so it completely soaks it. Allow a few seconds so the solution permeates the paper and then pour off the excess liquid.
- Place a tiny bit of zinc or iron onto the damp filter paper. The copper crystals trace their way outward from this metal. These crystals develop within an hour or two. They are delicate, so you may want to view them using a magnifying glass.
How to Grow Copper Metals Crystals Simulating Native Crystals
Copper exists in native form, meaning it occurs as a pure element in nature and not just in compounds. This next method of growing copper metal crystals simulates the formation of copper crystals in the environment. The principle is exactly the same as in the first method. While you can use either iron or zinc, iron more closely resembles the natural process because it is an abundant element in the Earth’s crust.
- Copper(II) sulfate pentahydrate
- Large test tube, graduated cylinder, or similar clear, narrow container
- Cotton balls or cotton pads
- Iron nails (or other objects)
- Non-iodized salt (NaCl)
- Pour 2-3 centimeters of copper sulfate into the bottom of the test tube.
- Add enough tap water to just cover the copper sulfate.
- Soak a cotton ball or cotton pad in water and gently press it onto the top of the copper sulfate
- Pour 1-2 centimeters of water on top of the cotton layer.
- Add enough water to just cover the salt layer.
- Push a second piece of damp cotton onto the salt layer.
- Place iron nails on top of the cotton.
- Add water so that it cover or at least partly covers the nails.
- Cap the tube and observe its contents each day. By the end of a week, the bottom of the test tube contains a blue-green copper oxide layer, sizeable copper metal crystals, and a translucent, nearly colorless liquid.
How to Grow Large Copper Metal Crystals Using Electricity
For big copper crystals, drive electrolysis using a power supply. It takes quite a while for large crystal formation (weeks or longer), so a battery just is not enough, but you want low voltage and especially low current.
- Container (borosilicate glass works well)
- Copper(II) sulfate pentahydrate
- Non-iodized salt (optional: You can add a bit if you like and see if you like the effect.)
- Copper for the anode and cathode
- Power supply (set to 1 to 5 volts and aim for less than 10 mA of current)
The anode is the source of the copper for the crystals, so it becomes depleted over time. So, choose a thick wire or perhaps a sheet of copper. The crystals form on the cathode. Usually, this is a copper wire, but you may want to add wiggles to support the weight of the crystals.
The crystal appearance depends on the current, the copper sulfate concentration, whether or not chloride (as from non-iodized salt) is present, and the distance between the anode and cathode. You want the anode and cathode as far apart from each other as possible in the container and not touching the side or bottom of the container walls.
- Make a copper sulfate solution. A good starting point is 100 grams of copper sulfate in 1 liter of water. If you like, add a bit of sodium chloride as a source of chloride ions. This tends to make the crystals less spindly and fragile and more blocky.
- Hang the anode and cathode in the container.
- Pour in the copper sulfate.
- Connect the anode to the (+) terminal of the power supply and the cathode to the (-) of the power supply.
Preserving Copper Crystals
When you are satisfied with your copper crystals, disconnect the power and remove the crystals from the copper sulfate solution. Gently rinse them with water and let them dry. Copper oxidizes and darkens in air. If you dislike this color, store copper crystals under oil or kerosene or seal them with polyurethane or resin.
If you chose not to seal the copper, you can brighten dark metal by spraying it with vinegar and rinsing it with water.
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- Hammond, C.R. (2004). Handbook of Chemistry and Physics (81st ed.). CRC press. ISBN 978-0-8493-0485-9.
- Petrucci, Ralph H.; Harwood, William S.; Herring, F. Geoffrey (2002). General Chemistry – Principles and Modern Applications (8th ed.). Prentice Hall. ISBN 0-13-014329-4.
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