Mars2atk - 9-11-2005 at 06:20
Hi, i've got an assignment due and i have no idea where to even start. We need to come up with a way to separate a solid mixture of Nickel
carbonate and Magnesium carbonate. They basically have to be separated into a pile of solid Nickel carbonate and another of Magnesium carbonate.
Thanks in advance!
Eclectic - 9-11-2005 at 06:36
Check solubilty in aqueous ammonia.
Mars2atk - 9-11-2005 at 07:13
Would that give me a solution of Ni and Mg ions and a precipitate of Ammonium carbonate?
Mars2atk - 9-11-2005 at 08:00
Actually, would nickel carbonate dissolve in a concentrated base? Bacause i'm pretty sure that magnesium carbonate won't, so it nickel did
then i'm halfway there.
Eclectic - 9-11-2005 at 08:31
Nickel ammonium carbonate may be soluble.
Mars2atk - 9-11-2005 at 08:40
yeah ive found out that Nickel carbonate is soluble in ammonia whereas magnesium carbonate isn't. I'm just stuck as to how the actual
reaction is supposed to be written.
Mars2atk - 9-11-2005 at 09:32
Ok so i think i may have just figured out how to separate them, i just need help in confirming whether its correct and the actual written reaction.
Add ammonia to the mix, the nickel carbonate dissolve and i can filter the Mg carbonate out. Then if i heat the solution, the ammonium carbonate
should decomp to for ammonia and carbon dioxide which will just bubble off and leave me with a aqueous solution of water and Ni ions. So if i add
aqueous sodium carbonate, nickel will precipitate back out as nickel carbonate.
Does that sound right?
Eclectic - 9-11-2005 at 10:21
Except than maybe all you have to do is boil off the ammonia and heat residue to dryness. Experiment.
Nickel ions are not going to stay dissolved in water by themselves. Either the carbonate or possibly the hydroxide will precipitate
[Edited on 9-11-2005 by Eclectic]
chemoleo - 9-11-2005 at 12:44
Aren't you just forming the Ni complex ion, which dissolves when it's i.e. Ni(NH3)6CO3 (you have to check with analogous examples how many
NH3's are complexed by Ni2+).
After this, you have to remove the complexed ammonia however. I am not sure that if you boil the Ni solution to dryness (after MgCO3 was filtered
off), the complexed NH3 will evaporate as well. Rather, you are likely to get decomposition products, from NiCO3 to NiO to Ni hydroxy carbonates, and
so on.
Are you allowed to use any other chemicals? In that case it's simple of course.
Also, did you check if Mg-bicarbonate is soluble? If so, you could bubble the solution with CO2, bring the MgCO3 into solution, filter the NiCO3, and
boil to dryness. But using CO2 is another chemical I suppose.
12AX7 - 9-11-2005 at 13:48
Yeah you could dissolve a little in club soda (plain carbonated water, concentrated carbonic acid I suppose you could say), I don't know how much
though.
I remember reading about this technique (Mg bicarb solution) being used to preserve acid-process paper, to neutralize residual acid to keep it from
decaying further.
Ammonia sounds like the best solution. If nickel ammonium carbonate (as opposed to nickel tetramine carbonate) is the soluble compound, you'll
want to use ammonium carbonate. Otherwise, ammonia solution would be the way to go.
Tim
Mars2atk - 9-11-2005 at 21:41
I'm just getting a little confused here. So if i dissolve the mix in ammonia, i'd be able to filter the MgCO3 out. That part i get, but the
Ni would form a complex Ni ammonium carbonate ion that will most likely just boil off, or would the NiCO3 actually form but just decomp in heat
anyway?
I'm allowed to use any chemicals i want, i just chose ammonia because i knew that MgCO3 wouldnt dissolve in it but NiCO3 would.
Mars2atk - 10-11-2005 at 06:11
Ok, so ive just found out that After being dissolved in ammonia, even after boiling til dryness, i'll be left with a NiO solid, i need to get
that back into NiCO3, unless someone has other ideas on how to separate them?
chemoleo - 10-11-2005 at 06:46
Well you are nearly there.
If you get to dissolve the NiCO3 with ammonia, you are left with MgCO3. The Nickel tetra(hexa?)amine carbonate is then boiled to dryness, and heated
under a flame in a crucible until only NiO or NiCO3 is left (high heat in order to make sure no NH3 is left). This is dissolved in HCl, heating will
be most likely necessary. Possibly H2SO4 will be better as it's less volatile.
Then, precipitate the NiSO4 by addition of Na2CO3, to form NiCO3 (precip) and Na2SO4.
Expenditure of chemicals: NH3, Na2CO3.
Mars2atk - 10-11-2005 at 07:42
Thank you everyone for all the help, i might just pass this assignment in the end.