Nails rusting in salt solution, white crystals

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Offline cvhorie

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Nails rusting in salt solution, white crystals
« on: 03/02/2014 12:23:59 »
My students do a familiar experiment, observing the rusting of iron nails in salt solution in test tubes. The expected reaction products, orange rust, black magnetite, and green/blue ferrous hydroxide (top to bottom), are usually described.
Consistently occasional students report that some white crystals are seen at the bottom of the tube (but I have not seen them).  My only guess is that they are hydrated ferrous chloride precipitate, actually light green but looking white in contrast with the black oxides.
Does anyone know what these crystals are?

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Offline chiralSPO

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Re: Nails rusting in salt solution, white crystals
« Reply #1 on: 03/02/2014 15:49:35 »
If they are using galvanized nails, there should be a fair amount of zinc salts produced. Depending on concentration and pH, you could  have some insoluble, colorless zinc (II) compounds forming crystals...

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Offline Bored chemist

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Re: Nails rusting in salt solution, white crystals
« Reply #2 on: 04/02/2014 21:16:29 »
You ruled out salt because...?
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Offline CliffordK

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Re: Nails rusting in salt solution, white crystals
« Reply #3 on: 04/02/2014 22:49:32 »
How much lab equipment do you have available?

Perhaps isolate some of the crystals, look at the structure under a microscope, and test the melting point. 

Also, as BC mentioned, you can check to see if they are soluble in water.