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Author: Subject: Looking for an ionic solid insoluble in water
kt5000
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[*] posted on 27-1-2015 at 11:41
Looking for an ionic solid insoluble in water


My daughter loves science projects and is obsessed with making crystals. We have made a store-bought crystal kit, monoammonium phosphate if memory serves, and we also made some copper(ii) chloride. The monoammonium phosphate + food coloring was unimpressive and seemed to be hygroscopic, and I was not about to send her away with a jar of copper(ii) chloride :D

I'm looking for an ionic solid that's insoluble in water and relatively non-toxic. Preferably colorful. I'm not sure if it has to be an ionic compound--that's just what I've made crystals from in the past. The solvents I have available are MeOH, EtOH, and acetone. Any ideas?

[Edited on 27-1-2015 by kt5000]
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[*] posted on 27-1-2015 at 11:54


There's more to life than being an ionic solid.
Rust is ionic, solid, and not soluble in water(well, very slightly soluble).

You can crystallise aspirin or naphthalene from alcohol, but there's no way round the fact that they are way more toxic than ammonium phosphate.
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[*] posted on 27-1-2015 at 12:13


This thread may be helpful to you:

http://www.sciencemadness.org/talk/viewthread.php?tid=5529




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kt5000
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[*] posted on 27-1-2015 at 12:37


Quote: Originally posted by unionised  

You can crystallise aspirin or naphthalene from alcohol, but there's no way round the fact that they are way more toxic than ammonium phosphate.


I remember aspirin making thin yellow needle-like crystals. I was hoping for something more like a CuSO<sub>4</sub> or CuCl<sub>2</sub> crystals. Colorful and big enough to look pretty cool.
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[*] posted on 27-1-2015 at 12:59


Sweeping generalisations are always wrong, but there are not many cvoloured organic compounds of low(ish) toxicity that crystallise well.
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kt5000
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[*] posted on 27-1-2015 at 13:16


Damn. I can always buy her some pretty quartz, amethyst, etc. on eBay. My goal, though, is to find a fun way to teach her about solubility and crystal structure.
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[*] posted on 27-1-2015 at 13:40


Buy some alum. Make it chrome alum if you want color. It's not overly poisonous, just don't touch it more than you need to (like any grown crystal of soluble compound, the moisture in skin degrades the appearance)

Sugar is edible, borax is also ideal. For colors you really need to look at transition metal compounds but none of them are exactly health products. Experiments should be taught to be handled carefully and hands washed afterwards either way.




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[*] posted on 27-1-2015 at 13:52


Quote: Originally posted by kt5000  
The monoammonium phosphate + food coloring was unimpressive and seemed to be hygroscopic,


Then you are probably not doing it right. I had good results with that many years ago. Growing nice crystals is never easy.




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[*] posted on 27-1-2015 at 16:48


You want to grow crystals of something that's soluble in water- insoluble things are much harder to grow nice crystals of. Alum works nicely, and I've read that you can extract the dyes from highlighters, and these stick very well to the aluminum ion, s0o they can be used to colour the crystals. Ammonium magnesium sulphate also works well, and you can add small quantities of copper or nickel salts to dope them into being blue or green.



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[*] posted on 27-1-2015 at 16:58


I know this isn't a crystal, but you could precipitate copper carbonate from a copper sulfate solution with baking soda.



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