How the tin hedgehog forms?
Metal zinc (Zn) reacts with tin (II) chloride (SnCl2) presented in the solution. The following reaction occurs:
SnCl2 + Zn → Sn + ZnCl2
Tin precipitates from the solution as beautiful crystalline structures. Tin crystals grow directly on a surface of zinc pellet. That’s how the tin hedgehog appears.
Why do tin needles appear?
We have already found out where the tin comes from during our experiment. It is forced out of the tin chloride solution (SnCl2) by zinc.
But why does tin precipitate on the zinc pellet as such fancy needles?
The reaction between SnCl2 and Zn takes place nearby the zinc pellet surface. Tin which is a product of this reaction grows as needle-like crystalline structures. This process is called crystallization.
Each metal we know from the periodic table of elements, possesses a set of unique chemical and physical properties including specific structure of crystals. The peculiarity of tin is that its crystals are strong and elastic enough. Moreover they have significantly different speed of growth in various directions, which results in the appearance of long needles.
Can we obtain a hedgehog, using some other salt, but not SnCl2?
Let us refresh our memory about what happens in this experiment. Zinc reduces SnCl2 to metal tin which crystallize from the solution to form metallic needles.
If we want to replace SnCl2 with another salt, we should understand first, which requirements it has to meet. Here is a short-list of them:
the salt should be well-soluble in water and quite stable as well;
the atom of metal from this salt should react readily with zinc and oxidize it to Zn+2 (the metal itself should be reduced to an elementary substance);
metal should be capable to form solid crystalline structures;
the yielding metal should not react with oxygen from air (otherwise it would oxidize, destructing needles).
It is not too hard to find an appropriate salt. However a hedgehog would not appear. Each metal has unique properties of crystals. And only the tin is capable to form needles.