Tin hedgehog
A zinc pellet turns into a hedgehog!
Reagents
Safety
- Put on protective gloves and eyewear.
- Conduct the experiment on the tray.
- Do not put the cap on the vial.
- Do not allow chemicals to come into contact with the eyes or mouth.
- Keep young children, animals and those not wearing eye protection away from the experimental area.
- Store this experimental set out of reach of children under 12 years of age.
- Clean all equipment after use.
- Make sure that all containers are fully closed and properly stored after use.
- Ensure that all empty containers are disposed of properly.
- Do not use any equipment which has not been supplied with the set or recommended in the instructions for use.
- Do not replace foodstuffs in original container. Dispose of immediately.
- In case of eye contact: Wash out eye with plenty of water, holding eye open if necessary. Seek immediate medical advice.
- If swallowed: Wash out mouth with water, drink some fresh water. Do not induce vomiting. Seek immediate medical advice.
- In case of inhalation: Remove person to fresh air.
- In case of skin contact and burns: Wash affected area with plenty of water for at least 10 minutes.
- In case of doubt, seek medical advice without delay. Take the chemical and its container with you.
- In case of injury always seek medical advice.
- The incorrect use of chemicals can cause injury and damage to health. Only carry out those experiments which are listed in the instructions.
- This experimental set is for use only by children over 12 years.
- Because children’s abilities vary so much, even within age groups, supervising adults should exercise discretion as to which experiments are suitable and safe for them. The instructions should enable supervisors to assess any experiment to establish its suitability for a particular child.
- The supervising adult should discuss the warnings and safety information with the child or children before commencing the experiments. Particular attention should be paid to the safe handling of acids, alkalis and flammable liquids.
- The area surrounding the experiment should be kept clear of any obstructions and away from the storage of food. It should be well lit and ventilated and close to a water supply. A solid table with a heat resistant top should be provided
- Substances in non-reclosable packaging should be used up (completely) during the course of one experiment, i.e. after opening the package.
FAQ and troubleshooting
Try using another bottle nozzle. It should fit snugly in the bottle. And, of course, you can always ask an adult for help.
Yes, of course, you can. But be sure to take a cap from a bottle meant for liquids! Otherwise, you won’t be able to close the bottle tightly enough.
Don't worry! Just continue the experiment.
If this happens, it’s best to start the experiment over.
No, unfortunately, you will not be able to keep the hedgehog long-term. The tin needles are very fragile and thin, and will immediately stick together if you remove the hedgehog from the solution. You can keep your hedgehog in the SnCl2 solution for some time, but not for too long. If you shake the test tube even a little, the needles will stick together. And with time, the solution will become cloudy and a precipitate will form. We recommend taking a picture of the hedgehog while it is beautiful and fresh.
Step-by-step instructions
First, prepare the tin chloride SnCl2 solution.
Now submerge a piece of a more active metal, zinc Zn, in the tin salt solution and see what happens.
Expected result
A zinc pellet transforms into a prickly hedgehog!
Disposal
Please refer to local regulations when disposing of chemicals. Dispose of other solid waste with household garbage. Pour leftover solutions down the sink. Wash with an excess of water.
Scientific description
Metals in their metallic form are made of positively-charged particles 
embedded in a negatively-charged cloud of electrons 
. Particles of some metals like to reside inside such a cloud more than others.
In our experiment, tin Sn 
would rather chill inside a cloud of electrons, whereas zinc Zn 
is relatively more inclined to float on its own as a charged particle (or, as chemists would say, an ion). When we
place a zinc pellet in a solution containing tin ions Sn2+ , the tin ions "pull” the “electron blanket" over 
, turning into metallic tin, and zinc ventures out into the solution 
.
The tin particles do not just settle all over the place randomly; they prefer a
certain way of "sitting" next to each other. Chemists call this crystal structure. This is
why tin forms elegant needles and does not cover the zinc pellet evenly. Other substances, meanwhile, have
different crystal structures. If you take a solution containing, say, copper ions (CuSO4, for one) instead of
tin ions, you won't create a needly hedgehog 
, but rather some completely different beast 
.
Even tin itself can have many crystal structures. At very low temperatures, tin prefers a different way of packaging itself, which greatly affects its properties. Solid pieces of tin turn brittle and crumble easily. This phenomenon is called "tin pest," and it can cause a lot of trouble if you rely on something made of tin when it's freezing cold. Some say that polar explorer Robert Scott learned this the hard way, as his expedition found itself in the middle of the frozen Antarctic desert with no way to get warm: the cans holding their fuel were soldered with tin, which crumbled in the cold and let all their fuel leak away.
How does the tin hedgehog form?
The zinc metal (Zn) reacts with the tin(II) chloride (SnCl2) present in the solution. The following reaction occurs:
SnCl2 + Zn → Sn + ZnCl2
During the reaction the tin precipitates from the solution as beautiful crystals. The tin crystals grow on a surface of the zinc pellet. That’s how the tin hedgehog appears.
Why do tin needles appear?
We have already worked out where the tin comes from during the experiment. It is taken out of the tin chloride solution (SnCl2) and replaced by the zinc.
But why does tin precipitate on the zinc pellet as fancy needles?
The reaction between SnCl2 and Zn takes place near to the surface of the zinc pellet. Tin, which is a product of this reaction, grows as needle-like crystalline structures. This process is called crystallization.
Every metal possesses a set of unique chemical and physical properties, such as a specific structure for its crystals. Crystals of tin are strong and relatively elastic, and the speed of crystal growth in one direction is faster than the speed of crystal growth in other directions, which results in the appearance of long needles.
Can you grow hedgehogs from other metal salts?
Let's remind ourselves what happens in this experiment. Zinc reduces the tin in the SnCl2 solution to form metallic tin, which crystallizes from the solution as metallic needles.
If we want to replace SnCl2 with another salt, there are some requirements that need to be met, such as:
-
the salt should be readily soluble and stable in water
-
the metal from the metal salt should react readily with zinc to oxidize it to form Zn2+ (the metal from the salt is reduced to its uncharged, metal form)
-
the metal should be able to form solid crystalline structures
-
the metal from the salt should not react with oxygen from the air once in its metal form (if the metal needles are oxidized, they would be destroyed).
Although it is not too hard to find an appropriate metal salt, a hedgehog may not appear. The crystals of each metal have unique properties, and tin forms good needles.
Follow up
What happens if I dilute the SnCl2 solution before making the hedgehog?
Repeat the experiment, but dilute the tin chloride solution two-fold first; you can use ordinary drinking water for this. Filtered water is best, or mineral water that does not contain any additives. Do not use soda water.
When we dilute the salt solution, we increase its volume, but because the overall number of salt molecules remains the same the solution becomes less concentrated. This decrease in tin chloride concentration results in longer tin needles, which makes the hedgehog look awesome, but the needles grow much slower. If the solution is diluted more than four-fold, the hedgehog forms much too slowly.
Do not forget to take a photo of your hedgehog!
That’s interesting!
Can I keep the hedgehog?
Unfortunately there is no way to keep the hedgehog. Tin needles are thin and fragile, which immediately collapse when you take the hedgehog out from the solution. The tin needles will collapse even if you leave the bottle cap open and evaporate the solution slowly; the needles break down under their own weight. It is possible to keep the hedgehog in the solution, although not for long periods of time. A gentle shake of the hedgehog in solution will crush the needles. In addition, the aqueous tin(II) chloride (SnCl2) solution is quite unstable in air; the solution soon turns cloudy and a precipitate forms. Tin needles also lose their bright silver shine. We recommend that you take a photo of your hedgehog soon after it has formed and before it degrades.
Tin disease: how can a metal be “sick”?
To call the metal that precipitates in our experiment tin is not entirely correct. Tin can be present in two different forms, called “modifications”; white tin and grey tin. White tin is a soft and flexible solid and has a silver color. It is white tin that forms as the needles of our hedgehog. White tin exists at temperatures higher than 13.2оС (–8.24oF), and it was a popular material in the 19th century and was used for buttons on military uniforms, flasks, plates and other housewares, and children's tin toy soldiers.
However, if you cool tin below 13.2оС (–8.24oF), it will gradually become a fragile, crumbly, grey substance, known as grey tin. When tin is put into a deep freeze (≈ –30оС / –22oF) it collapses to form a grey powder. Interestingly, if you place a piece of grey tin in contact with a piece of white tin, the white tin becomes “infected” and turns into grey tin. This phenomenon is known as tin disease.
There are a number of interesting, often sad, stories connected with tin disease.
Tin disease may have been a key factor in the famous and courageous explorer Robert Scott's tragic fate. His expedition to the South Pole was his last. Explorers typically used liquid fuel contained in metal containers/barrels that were sealed with tin plugs. The average temperature in the Antarctic is −60оС (–76oF) in winter and just −25– −45оС (–13– –49oF) in summer. The white tin may have turned into crumbly grey tin and resulted in loss of essential fuel.
