Tin Hedgehog Experiment

5th September 2018

Chemistry

The tin hedgehog experiment is a simple piece of chemistry that involves tin crystals growing on a zinc pellet, transforming it into the likeness of our favourite spiky animal.

Chemistry has had an astounding impact on the modern world. Thanks to chemistry, we enjoy things like penicillin, soap and even the screen you’re reading this on. Chemistry is also good for a lot of experiments, like how to make a hedgehog out of tin! This is achieved by a single displacement reaction and it can be performed in two different ways.

  1. Grow a Tin Hedgehog Using Zinc

When a zinc pellet is left in a solution of tin (II) chloride (SnCl2), thin metal crystals begin to appear on the pellet surface. These spiky crystals accumulate over time and transform the round piece of zinc into what appears to be a tin hedgehog.

Materials Used

  • 5M solution of tin (II) chloride: different concentrations can be used, but it is important to note that these will affect the reaction time.
  • Zinc pellet: because it is round, the pellet will force the tin crystals to collect in a circular shape, creating the appearance of a hedgehog.
  • A vial, test-tube or clinical flask: your chosen container must have a larger diameter than the zinc pellet so that there is enough room for the crystals to gather and grow.

The Method

  • Fill your container half-way with tin (II) chloride
  • Place a zinc pellet into the solution
  • After 15 minutes, crystals will begin forming around the pellet
  • After 1 hour, crystal formation will be at its peak
  • This will result in a small tin hedgehog sitting at the bottom of your container

The tin hedgehog won’t stay around forever. Over time, the structure will collapse due to the weight of the metal crystals accumulated on the surface. Any movement of the container or structure will also lead to a collapse because of the fragility of the crystals.

A hedgehog in the woods

A tin hedgehog is an experiment that involves reacting tin (II) chloride with a zinc pellet. The result is a round ball covered in a thin, metal crystals.

The Tin Hedgehog Reaction

When these two substances are combined, a classic metal displacement reaction occurs. This is common in many interactions between metals, such as when copper sulphate and silver nitrate react to form a crystalline, tree-like structure. The equation for the tin hedgehog reaction is:

SnCl2 (aq) + Zn (s) → Sn (s) + ZnCl2 (aq)

The products of the tin hedgehog reaction are tin metal (Sn) and zinc chloride (ZnCl2). Because zinc is more reactive than tin, it is able to displace the tin metal by giving electrons to the tin chloride.

When the tin metal is freed, its atoms stack on top of each other as it begins to precipitate and deposit itself onto the surface of the zinc pellet. This creates the spiky metal crystals of the tin hedgehog.

Safety Precautions

  • Tin (II) chloride: this substance is an irritant and so it is important to ensure that your eyes and skin are always protected when handling this compound.
  • Zinc chloride: when tin (II) chloride and zinc react, zinc chloride is produced. This is very harmful to aquatic organisms and should not be poured down the sink or drain.

Always refer to MSDS guidelines for information on how to correctly dispose of substances. You should also always wear PPE (Personal Protective Equipment) when handling chemicals.

A tin hedgehog, which is made by reacting tin chloride with zinc

Image source: https://melscience.com/en/experiments/tin-hedgehog/

  1. Grow a Hedgehog Using Iron

The same experiment can be carried out using a piece of iron instead of a zinc pellet. If you want the tin hedgehog effect, a round piece of iron would have to be used. But if you’re purely interested in the crystal growth, an iron nail or wire is just as effective.

Materials Used

  • 1M solution of tin (II) chloride
  • Iron wire, nail or round chunk
  • Appropriate container e.g. a vial or test tube

The Method and Reaction

  • Fill your test tube with enough tin (II) chloride to cover the piece of iron
  • Suspend or place your piece of iron in the container
  • After 1 hour, crystals will begin forming
  • Leave it overnight to witness optimum crystal formation

As with the zinc pellet, iron is more reactive than tin and is, therefore, able to displace the tin metal from the tin chloride. The products of this reaction are tin metal and iron chloride (FeCl2). The equation for this is as follows:

SnCl2 (aq) + Fe (s) → Sn (s) + FeCl2 (aq)

The process then mimics the zinc pellet reaction, with the tin metal depositing itself onto the iron surface in the formation of thin crystals. While it may not result in the shape of a hedgehog, depending on the piece of iron used, the spiky exterior will still be there!

A fake hedgehog on display with conkers and autumn leaves

There are many different types of metal displacement reactions for you to try your hand at. These types of reactions do more than just grow beautiful crystal structures; they are also staples in thermite welding, steel making, extracting metals and even relief from acid indigestion!

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