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Author: Subject: FeCO3 oxidation
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[*] posted on 12-3-2013 at 20:56
FeCO3 oxidation

I just bought some HCl that looks yellowish (may be contaminated with Fe), and made some FeCl2 solution.
I added some NaHCO3 and FeCO3 precipitated. And i let it settle down. After some 15 mins i saw that some of it had vanished and there was some red stuff floating on surface.

I belive it is Fe2(CO3)3 .
Can anyone state the equation for the oxidation of FeCO3 ?

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[*] posted on 13-3-2013 at 08:15

What is probably happening is that the FeCO3 isn't terribly insoluble, and you get a small but finite concentration of Fe2+ in solution. Since this is exposed to oxygen in the air, and you have a basic solution, you get 4 Fe2+ + 8 OH- + O2 + 2 H2O --> 4 Fe(OH)3. Solutions of iron(II) are generally kept acidic to prevent this reaction.

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[*] posted on 13-3-2013 at 09:38

Quote: Originally posted by rstar  
I belive it is Fe2(CO3)3 .
Can anyone state the equation for the oxidation of FeCO3 ?

This has been covered elsewhere. Fe(III) carbonate is unlikely to exist, just like Cr(III) carbonate and Al(III) carbonate don't exist, at least not in watery media.

Your red stuff is ferric oxide hydrate. I've seen wet FeCO3 (insoluble) oxidise in air to ferric oxide hydrate quite quickly several times...

[Edited on 13-3-2013 by blogfast25]

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