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Author: Subject: Is drawing chalk pure enough?
Wolfram
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[*] posted on 31-10-2003 at 09:12
Is drawing chalk pure enough?


Is drawing chalk pure enough to use as CaCO3 in sythesis.
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Mumbles
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[*] posted on 31-10-2003 at 09:42


It depends on what the use of the CaCO<sub>3</sub> is in the reaction mechanism. Chances are it wont be though. Plain white chalk will be the most pure out of all the chalks. It will still be contaminated with Calcium Hydroxide, and Magnesium Oxide/hydroxide/carbonate.

It can be purified to some degree. Dissolve in an acid to make a soluble salt(ie HCl). Filter to remove any impurities, then add a solution of a different carbonate salt. Sodium Carbonate and Potassium Carbonate are very cheap and readily available. This will give a precipitate with nearly all Calcium and Magnesium Carbonate. If the carbonate ion is needed this would probably work.

If you need the calcium ion, you're better off to go buy some Calcium Chloride ice melter or Dri-rite. Just dissolve in water and add the carbonate solution like mentioned before. If using ice melter me sure its just CaCl<sub>2</sub>, and don't worry if it doesn't all dissolve, thats just the CaCO<sub>3</sub> coating.

[Edit] fixed some grammar and spelling.

[Edited on 10-31-2003 by Mumbles]

[Edited on 10-31-2003 by Mumbles]
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[*] posted on 31-10-2003 at 11:25
CaSO4


Where I come from drawing chalk is pure CaSO4, not carbonate.

Pure 'chalk' as in chalk cliffs etc. are CaCO3, but to my knowledge, drawing chalk is always CaSO4.

And it is confirmed at least in Oxford's Dictionary of Chemistry under the entry for calcium sulphate.
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[*] posted on 9-11-2003 at 05:33


I agree with PrimoPyro that drawing chalk is calcium sulphate.

If you want calcium carbonate for synthesis, buy "precipitated chalk" from a brewing/winemaking supplier.




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[*] posted on 9-11-2003 at 15:43


Depending on what you want it for you might be able to get away with using garden lime (crushed limestone) which is a lot cheaper).
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[*] posted on 9-11-2003 at 18:35


Garden lime is Ca(OH)<sub>2</sub> mainly. There is 10% Mg(OH)<sub>2</sub> in what is available here. I'm sure theres carbonate and oxide in there too. It would work if you needed the OH<sup>-</sup> ion probably. If the Calcium ion was a catalyst it would probably work too. I know garden lime can be used to make glycerine from oil, and the AN/Urea method to Guanidine Nitrate. There are definatly other things, but nothing that comes to mind.
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[*] posted on 11-11-2003 at 11:01


The garden lime I have is the carbonate.
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[*] posted on 11-11-2003 at 11:11


Quote:
Originally posted by Mumbles
Garden lime is Ca(OH)2 mainly.


Quote:
Originally posted by unionised
The garden lime I have is the carbonate.


Lime is a general term for several calcium compounds. I've seen it used for calcium oxide, calcium hydroxide and calcium carbonate.




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