Silver Crystal Tree Chemistry Demonstration

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Silver Tree Chemistry Experiment
The silver tree chemistry experiment uses a redox reaction to grow silver crystals on a copper holiday tree.
Silver often forms dendrites, which resemble metal crystal trees. (Rob Lavinsky / iRocks.com)
Silver often forms dendrites, which resemble metal crystal trees. (Rob Lavinsky / iRocks.com)

In this simple chemistry demonstration or crystal project you’ll grow a silver crystal tree. This is a variation of the classic method of growing silver crystals on a copper wire.

Silver Crystal Tree Materials

You only need two materials for this project:

  • Copper tree – Sheet of copper that has been cut into a tree shape or a tree made from copper wire
  • 0.1 M Silver nitrate solution

There are a few different ways to make the tree shape. One of the easiest is spiraling copper wire over a paper or cardboard cone to make a simple tree form.  Another method is wrapping thin copper wires around a thicker wire, leaving the ends of the thin wires out as branches. Another method uses tin snips to cut a tree shape out of a thin copper sheet.

Be careful to use uncoated copper. Because copper oxidizes in air, it is often treated or coated. If your copper has a coating, it’s not the end of the world. Dipping it into dilute hydrochloric acid (muriatic acid) and rinsing it in water removes most coatings and exposes the copper metal.

Grow a Silver Crystal Tree

All you is place the copper tree into the silver nitrate solution. Silver is reduced on the copper, forming silver crystals. Crystals begin forming immediately and should be visible within an hour. Meanwhile, the solution increases in concentration of copper(II) ions and develops a blue-green color.

You can allow the silver crystal tree to sit in an undisturbed location for a day or two for peak crystal growth. When you are finished growing the silver crystals, carefully remove the tree from the solution and use it as a decoration. Silver is a noble metal, so it resists tarnish.

How It Works

A single displacement reaction is responsible for crystal formation:

2 AgNO3 + Cu → Cu(NO3)2 + 2 Ag

2 Ag+ + Cu → Cu2+ + 2 Ag

The silver nitrate in water dissociates into silver and nitrate ions. The silver and copper “trade places” so that silver metal takes the place of some copper, while some copper goes into solution. The copper ions change the color of the liquid, making it blue. This is also an example of a redox reaction written as its net ionic equation.

Silver is very far down the metal reactivity series. What this means is copper isn’t the only metal that works for this project. For example, silver also replaces mercury. If you happen to have mercury sitting around, you can place a bead into a container of silver nitrate and see the same effect.

Dendritic Silver Crystals

Silver crystals form dendrites, which look like ferns, branches, or trees (depending who you ask). Another simple project is to place a copper wire in silver nitrate solution and view crystal growth using a magnifying glass or microscope. The intricate structure of the metal crystals develops as you watch!

Here’s an example of the reaction on a piece of copper:

Is silver nitrate too expensive? Another redox reaction coats copper onto zinc and makes copper holiday ornaments. There are other metal crystals you can grow, too.

References

  • Lide, David R., ed. (2009). CRC Handbook of Chemistry and Physics (90th ed.). Boca Raton, Florida: CRC Press. ISBN 978-1-4200-9084-0.
  • Todd, Robert H.; Allen, Dell K.; Alting, Leo (1994). “Surface Coating”. Manufacturing Processes Reference Guide. Industrial Press. ISBN 0-8311-3049-0.