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Visual fractional distillation demo - thwarted

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JeffEvarts
#1
Dec5-12, 08:37 PM
P: 34
I wanted to do a demo of fractional crystallization that would have a nice visual result. I had intended to make a saturated solution of ferric chloride, nickel chloride, and sodium chloride, put the solution in a very broad shallow petri dish, and allow natural evap to produce concentric colored rings. Each chloride has at least a 2x difference in solubility from the next.

The yellow band (ferric, 60g/100ml) outide the green band (nickel, 300g/100ml) outside the white band (sodium, 650g/ml) - it seemed simple and elegant.

Unfortunately, nickel and ferric chloride are "dangerous", so chemical companies won't ship them to non-business, non-educational addresses. :( I am NOT trying to get around the law here, nor am I soliciting someone to do so.

I'm asking two questions:
1) Would this experiment have worked, or do I misunderstand fractional distillation?
2) Are there safer chemicals that would yield the same results?

Disclaimer: I am a chemistry noob. I used all chlorides because I didn't want cross reactions between the chemicals to spoil the fun, and the carbonates and hydroxides I found weren't sufficiently soluble to make the experiment practical.
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chemisttree
#2
Dec6-12, 12:50 AM
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I don't think you have a misunderstanding about fractional crystallization but it appears your spell check is replacing several instances of the word 'crystallization' with 'distillation'. Because you are using a strongly colored ferric salt, it will stain everything that comes out of solution... even if you manage to produce the concentric rings effect. I don't see how you intend to do that part of it but if you did, you would get brown crystals around brown crystals and brown crystals in the middle.

This sounds like an analog to circular chromatography of colored dyes onto a towel. A mixture of dyes with different rf values is spotted in the center of a towel and solvent carefully added. As the spot spreads, the colors separate out producing a tie-dye effect.

It might work if you grow the crystals on a stick and allow the solution to slowly evaporate. In theory you should get three blobs of different crystals. Neat if you can do it. It will probably work best with a tall, skinny glass like you get with cocktail olives. I've found that phosphoric acid (85% or somewhat more dilute) decolorizes ferric chloride in solution to a nearly colorless light purple. It might just work for a thin solid layer staining a surface. That might be a way to rinse the the Ni and NaCl crystals to decolorize the FeCl3 somewhat.


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