Trying to make some chrome alum ( KCr(SO4)2 ) for crystal growing.
I have a couple of small jars of Cr(III) acetate, and access to some common sulfates ( NH4, K, Mg, Cu) - but not sulfuric acid.
Solubility data dredged up so far: (@20C, g/100g in water)
KCr(SO4)2 : 24
Cr acetate : 67.5
Cr sulfate : 220
K acetate : 286
K sulfate : 13
So i'm looking at this and wondering if simply combining the cr acetate with K sulfate will result, at some point, with KCr(SO4)2 crystalizing out,
leaving the acetates in solution? This isn't something i've ever tried to work out before, and to be honest i'm not really sure how.
Advice appreciated . Alternative route suggestions also appreciated.
I have nitric acid ( lots of it - but no sulfuric *sigh*), so going via nitrates is possible.
[Edited on 3-4-2017 by Twospoons]diddi - 3-4-2017 at 14:19
Sulfuric acid can be purchased at most auto stores as top up for car batteries. It is clean and does not need processing like the drain cleaning
products.Twospoons - 3-4-2017 at 14:29
Ah, this might be simpler:
CuSO4 : 32 g/100g
Cu acetate : 7.2 g/100g
So combining CuSO4 with Cr acetate, I should get copper acetate crytalizing out first, leaving Cr sulfate in solution?
I've looked for battery acid in auto shops, and never found any. Seems to be harder to find in NZ.
[Edited on 3-4-2017 by Twospoons]Dmishin - 4-4-2017 at 02:37
I am pretty sure that mixing chromium acetate with excess of univalent sulfate will let you crystallize alum. Did not tried exactly this process, but
did similar things several times.
I would recommend trying NH4 sulfate, since it is more soluble than K2SO4woelen - 4-4-2017 at 03:25
There may be one issue which spoils things with acetate. The acetate ion is a good coordinating agent and I expect it to be tightly bound to the
chromium ion. The salt actually is an acetato complex of chromium(III).
Adding H2SO4 most likely (slowly) breaks away the acetate from the Cr(3+) ion and makes acetic acid, but I expect that adding CuSO4 to Cr-acetate does
not lead to much useful. I think that most of the acetate will remain attached to the chromium ion.CharlieA - 4-4-2017 at 18:01
I am pretty sure that mixing chromium acetate with excess of univalent sulfate
Please enlighten me...what is univalent sulfate? A sulfate salt of a univalent cation?Fantasma4500 - 5-4-2017 at 10:06
certainly will still be Cr Ac impurities if you just try to crystallize out most, maybe if you form large crystals you can sort out the crystals
supposing both compounds wont cocrystallize
i would suggest --> carbonate / hydroxide, then dissolving that in acid
