Tin Hedgehog Experiment
Grow Tin Metal Crystals
Metal crystals are intricate and beautiful. They are also surprisingly easy to grow. In this experiment, learn how to grow tin crystals that display a spiky appearance that make them look like a metal hedgehog.
Tin Hedgehog Materials
0.5 M tin (II) chloride solution (SnCl2)
test tube or vial that is larger in diameter than the zinc
The rounded hedgehog shape forms around a pellet of zinc, but you can substitute any chunk of zinc metal. Since the reaction occurs at the surface of the metal, you may also use a galvanized (zinc coated) object in place of the zinc pellet.
Grow a Tin Hedgehog
Pour tin chloride solution into a vial. Don’t fill it up all the way because you need room for the zinc.
Add the zinc pellet. Set the vial somewhere stable, so it won’t get bumped or jarred.
Watch the delicate tin crystals grow! You’ll see the beginning of a spiky hedgehog shape in the first 15 minutes, with good crystal formation within an hour. Be sure to take pictures or video of the crystals for later, since the tin hedgehog won’t last. Eventually, the weight of the fragile crystals or movement of the container will collapse the structure. The bright metallic shine of the crystals will dull over time, plus the solution will turn cloudy.
Chemistry of the Reaction
In this experiment, tin (II) chloride (SnCl2) reacts with zinc metal (Zn) to form tin metal (Sn) and zinc chloride (ZnCl2) via a substitution or single displacement reaction:
SnCl2 + Zn → Sn + ZnCl2
Zinc acts as a reducing agent, giving electrons to the tin chloride so that the tin is free to precipitate. The reaction begins at the surface of the zinc metal. As the tin metal is produced, atoms stack on top of each other in a characteristic form or allotrope of the element. The fern-like shape of the zinc crystals is a characteristic of that metal, so while other types of metal crystals may be grown using this technique, they won’t display the same appearance.
Grow a Tin Hedgehog Using an Iron Nail
Another way to grow tin crystals is using zinc chloride solution and iron. Unless you use a round chunk of iron, you won’t get a “hedgehog”, but you can get the crystal growth, just the same.
iron wire or nail
0.1 M tin chloride
Note: You don’t need to make up a new tin chloride solution. If you have solution from the reaction with zinc, you can use that. The concentration mainly affects how quickly the crystals grow.
Suspend the iron wire or nail in a test tube containing tin chloride.
After about an hour, crystals will start to form. You can examine these with a magnifying glass or by removing the wire and looking at the crystals under a microscope.
Allow the iron to remain in the solution overnight for more/larger crystals.
Once again, this is a simple displacement chemical reaction:
Sn2+ + Fe → Sn + Fe2+
Safety and Disposal
As always, it’s good practice to wear safety goggles and gloves when performing chemistry experiments.
When you have finished the experiment, you can rinse the chemicals down the drain with water.
Use a magnifying lens to compare tin crystals grown on the zinc and iron surfaces.
You may wish to experiment with how changing the concentration of the zinc chloride solution or temperature of the solution affects the crystal growth rate and appearance.
Try to grow other metal crystals using this technique. Keep in mind the resulting crystals might not resemble a hedgehog. To choose a subject, find a metal salt that is soluble in water, does not oxidize too quickly in air, yet can react with zinc or iron (or other metal) to form crystals. The metal needs to be more reactive than tin or the substitution won’t proceed. It’s also a good idea to consider the toxicity of the metal, for personal safety and chemical disposal. You can consult the solubility rules to select good candidates for further experimentation.