bleckster
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Dehydrating sodium carbonate
Hi there,
I bought some anhydrous sodium carbonate from someone on eBay and I suspect it might not be anhydrous. Can it be dried in the oven the same way epsom
salts can?
Appreciate any help.
PS. I have confirmed that it is indeed sodium carbonate. A saturated solution gives a ph of 11 and adding HCl to it precipitated sodium chloride.
[Edited on 14-11-2013 by bleckster]
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Crowfjord
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Mood: Ever so slowly crystallizing...
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Drying in an oven is fine. And it should fizz vigorously when acid is added (carbon dioxide evolved). Seems like that would be more apparent (and
indicative of carbonate) than salt precipitation...
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barley81
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Maybe try heating a small sample in a flame-dried crucible and measuring the decrease in mass? Then you'll avoid the trouble of drying the whole lot
in the oven.
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bleckster
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Duh, you know what, I should have looked for its decomposition temperature (400°C) and that would have answered this very basic question for me.
I forgot to mention that when I did the hydrogen chloride test it did evolve carbon dioxide. I did that test because I saw it on a site somewhere as
one of the ways to test for sodium carbonate. That, along with the pH test, seemed pretty logical to me. I don't know how definitive it is. Maybe
someone else knows a few more tests that would clinch it? I'm always interested to know what I don't know. :-)
Here is something interesting--in http://www.fao.org/ag/agn/jecfa-additives/specs/Monograph1/A... it says this:
For all forms, heat the sample first at about 70°, then gradually raise the temperature and finally dry at 250-300° to constant weight.
Why do you suppose you have to heat it to 70 first, as opposed to just blasting it at 250?
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bleckster
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Also, I believe I mentioned that I made a saturated solution when doing the pH test. 2 grams dissolved in about 10 mL of water, so that fits nicely
with sodium carbonate's solubility (215g/L @ 20C).
The sodium bicarbonate needed more than twice that much water (I didn't measure the amount, just added water drop wise until everything dissolved--I
was using arm & hammer so I knew what that was for sure).
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