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Author: Subject: Iron II Sulfate Ammonia Complexes
crestind
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[*] posted on 7-4-2015 at 17:01
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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[*] posted on 7-4-2015 at 17:14


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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[*] posted on 7-4-2015 at 17:43


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.


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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[*] posted on 7-4-2015 at 20:03


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.


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:

Quote:

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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