crestind
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Iron II Sulfate Ammonia Complexes
Got a few questions about Iron II Sulfate that hopefully some pros here might be able to offer some insights.
I start with Iron II Chloride (I made it by mixing steel wool and pool hydrochloric acid). I evaporate the solution to dryness, mix with some 50%
Sulfuric acid, and then I get Iron II Sulfate.
Now I know that if an oxidizing agent such as H2O2 or Nitric Acid is added to the mix, the Iron II Sulfate will be oxidized into Iron III Sulfate. But
does a solution of HCl, Iron II Sulfate, and Sulfuric Acid alone also result in a reaction into the ferric when heated strongly? Same question also
for Iron II Sulfate + Sulfuric and high heat.
The second part of my question was regarding getting Iron II Sulfate dissolved into pure sulfuric acid. I saw online that this chemical is listed as
being only marginally soluble in sulfuric.
However, I noticed that ammonium sulfate is soluble in pure sulfuric (I've mixed the two before). Now does this mean that Ammonium Iron Sulfate would
also be soluble in sulfuric acid? As I understand it, Ammonium Iron Sulfate is basically a metal ammine complex, so the ammonia ion actually brings
the iron into solution, with the sulfate being the other ion.
Some links I was looking over to try and understand this...
http://en.wikipedia.org/wiki/Ammonium_iron%28II%29_sulfate
http://en.wikipedia.org/wiki/Metal_ammine_complex
http://en.wikipedia.org/wiki/Double_salt
In a somewhat similar experiment, silver chloride is typically insoluble in pure sulfuric acid. However, I noticed if the sulfuric acid is saturated
with ammonium sulfate, a lot of the silver actually goes into solution, in much the same way that ammonia hydroxide would dissolve silver chloride.
Thank you for any insights you can provide.
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Amos
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Yes, when heated strongly, left in the air, or in low pH, iron(II) sulfate and chloride readily oxidize to the respective iron(III) salt. No, ammonium
iron(II) sulfate is not a metal ammine complex. Ammine complexes have ammonia(NH3) ligands connected to the metal atom; Ammonium iron(II) sulfate is
merely a typical ionic double salt, containing both Fe2+ and NH4+ ions in its lattice in crystalline form, and dissociating in solution to give
sulfate, ammonium, and iron(II) ions. The most obvious way to tell the difference is that the formula of Mohr's salt (ammonium iron(II) sulfate, is
(NH4)2Fe(SO4)2·6H2O, while a metal ammine complex, such as tetraammine copper(II) sulfate, has the
formula Cu(NH3)4SO4. It's the difference between NH4 and NH3 in the formula.
I'll let someone else give some info on the solubilities.
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blogfast25
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Quote: Originally posted by Amos  | | Yes, when heated strongly, left in the air, or in low pH, iron(II) sulfate and chloride readily oxidize to the respective iron(III) salt.
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Not without extra HCl or H2SO4 and even then it's a totally impractical way of producing Fe(III) sulphate or chloride. With air alone messy
hydroxysulphates/hydroxychlorides and ferric hydroxide form. Oxidation of Fe(II) salts in presence of their resp. acids and using oxidisers like
nitric acid or hydrogen peroxide is the most practical route for hobbyists.
Fe(III) sulphate and ammonium sulphate also form a double salt: ferric ammonium alum.
[Edited on 8-4-2015 by blogfast25]
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Amos
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The question being asked in the first place:
| Quote: |
Now I know that if an oxidizing agent such as H2O2 or Nitric Acid is added to the mix, the Iron II Sulfate will be oxidized into Iron III Sulfate. But
does a solution of HCl, Iron II Sulfate, and Sulfuric Acid alone also result in a reaction into the ferric when heated strongly? Same question also
for Iron II Sulfate + Sulfuric and high heat.
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I was under the impression that the original poster was more concerned about potential impurities or things going wrong, rather than looking for
practical routes to fF(III) salts, which hasn't been mentioned anywhere so far. Though yes, the Fe(III) compounds formed are fraught with impurities.
Many of the members here would beg to differ on very specific conditions being necessary for oxidation of Fe(II); For some it still seems to occur in
even the most ideal of storage conditions. And then there's this, from the iron(II) sulfate article on wikipedia:
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Upon exposure to air, it oxidizes to form a corrosive brown-yellow coating of basic ferric sulfate, which is an adduct of ferric oxide and ferric
sulfate:
12 FeSO4 + 3 O2 → 4 Fe2(SO4)3 + 2 Fe2O3
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