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Author: Subject: Iron(II) sulfate monohydrate from eBay - looks suspicious
DrMario
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[*] posted on 16-12-2014 at 23:27


In the morning I found the bottle to contain a clear solution.. and a ton of sh#t at the bottom. This is becoming a chore :(

I'm not even sure how to practically crystalize the Fe(II) sulphate from this 1L of solution.
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[*] posted on 16-12-2014 at 23:42


The reason why I say that it is hardly worth the effort to try to recover clean iron(II) sulfate from oxidized material is as follows:
- Iron(II) ion very easily is oxidized, especially in neutral to alkaline environments, when it is wet. Crystallizing from a solution cleanly only is possible if air is excluded, otherwise it will become covered by a brown crust of basic salt, which contains a mix of iron(II) and iron(III).
- The material is dirt cheap. If you have to use other chemicals besides the ferrous sulfate (e.g. sulphuric acid in order to get a clear solution) then the balance completely goes the wrong way.

With iron(II) chloride the situation is even worse. I once made that in solution and I had a nice blue/mint crystal. I took this out of the liquid, and within seconds the crystal turned yellow/green, it was oxidized almost immediately.

Making Mohr's salt is fairly easy. Just add ammonium sulfate to a solution of ferrous sulfate. Add a few drops of H2SO4 as well. Allow any solid material to settle, decant, and then allow to evaporate slowly. The acid and ammonium ions protect the iron(II) from aerial oxidation.




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[*] posted on 17-12-2014 at 00:42


Interesting thread. I, too, found typical industrial ferrous sulfate to be surprisingly unmanageable when I ordered some to "fortify" my lawn without adding any nitrogen, which is in any typical hardware store fertilizer and makes them grow faster instead of merely greener. I think I finally got a pound or so dissolved in my 25 gallon sprayer by adding a bit of citric acid to help stabilize it, and filtering the larger precipitate that did form with a couple layers of a tshirt. The water was still brownish-orange but didn't clog the Teejet nozzles. I had naively expected it to mostly dissolve like any other salt.

(some of you might remember my story of first trying to buy this at a now defunct feed store in Newark Delaware - merely asking for "can I buy a bag of iron sulfate" - and the hayseed counter sales lady asking "what kind o' drugs you makin'?" An example of people's bizarre paranoia about chemicals and their uses. And no, I didn't look like a drug dealer! Maybe she was a big Breaking Bad fan. Anyhow, they didn't have it...problem was it more of a horse feed store, apparently pure iron sulfate is more something used by cattle farmers. Not many of those in northern Delaware anymore.)
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[*] posted on 17-12-2014 at 06:31


DrMario, the first time I had ever even dealt with ferrous sulfate(which was homemade, by the way) like I said, I managed to change the color back after the inital oxidation, and I also kept a piece of steel wool in there 24/7, as well as a lot of sulfuric acid; kept this way it never went beyond green in an entire week while I was inactive in the lab. Later, I removed the steel wool, added EVEN MORE acid, and was able to let it just crystallize slowly in a container for over a month. The result was a crop of beautiful blue-green crystals underneath a golden-yellow solution, which by then was likely highly concentrated sulfuric acid. I don't know why it was so easy for me; maybe homemade grades are somehow more stable?



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[*] posted on 17-12-2014 at 07:38


Quote: Originally posted by No Tears Only Dreams Now  
DrMario, the first time I had ever even dealt with ferrous sulfate(which was homemade, by the way) like I said, I managed to change the color back after the inital oxidation, and I also kept a piece of steel wool in there 24/7, as well as a lot of sulfuric acid; kept this way it never went beyond green in an entire week while I was inactive in the lab. Later, I removed the steel wool, added EVEN MORE acid, and was able to let it just crystallize slowly in a container for over a month. The result was a crop of beautiful blue-green crystals underneath a golden-yellow solution, which by then was likely highly concentrated sulfuric acid. I don't know why it was so easy for me; maybe homemade grades are somehow more stable?


Very interesting. Could you quantify, at least roughly, the amount of H2SO4 vs. original "ferrous" sulphate?
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[*] posted on 17-12-2014 at 07:53


I think I initially prepared my ferrous sulfate using a 15-20% solution of sulfuric acid, and just periodically added more out of paranoia that I would spoil it after that initial hiccup occurred. This video provides a few helpful tips that I made heavy use of during the process: https://www.youtube.com/watch?v=BhqcPqaL_KQ&index=35&...

And now I'm off to prepare a solution of ferrous sulfate by displacing copper with iron!




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[*] posted on 17-12-2014 at 08:46


Quote: Originally posted by No Tears Only Dreams Now  
This video provides a few helpful tips that I made heavy use of during the process: https://www.youtube.com/watch?v=BhqcPqaL_KQ&index=35&...


Okay, that's it! Ferrous sulphate (and perhaps ferrous anything) is too much trouble.
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[*] posted on 17-12-2014 at 10:56


At my wit's end. :mad::mad::mad::mad::mad::mad:

I filtered the content of the bottle into a 2L beaker. I obtained a perfectly transparent green liquid, which I proceeded to heat to near boiling point on a hotplate. After about an hour of heating... the liquid is opaque with beige crap deposited on the bottom!

This is bullsh#t.

[Edited on 18-12-2014 by DrMario]
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[*] posted on 17-12-2014 at 11:15


Quote: Originally posted by DrMario  
At my wit's end. :mad::mad::mad::mad::mad::mad:

I filtrated the content of the bottle into a 2L beaker. I obtained a perfectly transparent green liquid, which I proceeded to heat to near boiling point on a hotplate. After about an hour of heating... the liquid is opaque with beige crap deposited on the bottom!


That will continue to happen if it's exposed to air. 4 Fe2+ + O2 + 2 H2O --> 4 Fe(OH)2+.

[Edited on 17-12-2014 by DraconicAcid]




Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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[*] posted on 17-12-2014 at 11:25


Quote: Originally posted by DraconicAcid  
Quote: Originally posted by DrMario  
At my wit's end. :mad::mad::mad::mad::mad::mad:

I filtrated the content of the bottle into a 2L beaker. I obtained a perfectly transparent green liquid, which I proceeded to heat to near boiling point on a hotplate. After about an hour of heating... the liquid is opaque with beige crap deposited on the bottom!


That will continue to happen if it's exposed to air. 4 Fe2+ + O2 + 2 H2O --> 4 Fe(OH)2+.

[Edited on 17-12-2014 by DraconicAcid]


I thought a sufficiently acidic environment should prevent this from happening.
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[*] posted on 17-12-2014 at 11:32


Quote: Originally posted by DrMario  
I thought a sufficiently acidic environment should prevent this from happening.


It happens faster under basic conditions, but it will still happen in acidic ones. Keep the air out.

Oh, and you didn't filtrate the solution- you filtered it. The solution you got afterwards was the filtrate.




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[*] posted on 17-12-2014 at 12:33


This just doesn't make any sense! Do you recall when earlier I said I was going to make some ferrous sulfate solution by displacing the copper from copper sulfate?

I put an excess of steel wool into some copper sulfate solution, added just a bit of HCl to get the reaction started, and was left with a very light green solution. At this point the solution really shouldn't be more than a tiny bit below pH 7. So I boiled that solution down to about 1/3 of the original volume, during which no color change occurred except a concentration of the green color. An hour in my freezer, and I got a nice little crop of fluffy FeSO4 crystals; EVERYTHING was exposed to the air during this time; there wasn't even a lid on the container in the freezer. I don't understand how one person can have such a negative experience with this compound when mine is perfectly content to remain unoxidized.

EDIT: I attached a picture; this stuff shows no signs at all of oxidation, IMO. I wish the crystals were a little more well-formed, though.

[Edited on 12-17-2014 by No Tears Only Dreams Now]

IMG_1199.JPG - 2MB




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[*] posted on 17-12-2014 at 12:41


Quote: Originally posted by DrMario  
At my wit's end. :mad::mad::mad::mad::mad::mad:

I filtrated the content of the bottle into a 2L beaker. I obtained a perfectly transparent green liquid, which I proceeded to heat to near boiling point on a hotplate. After about an hour of heating... the liquid is opaque with beige crap deposited on the bottom!

I know exactly how you feel. I did this too, but after noting the filtered solution was beige-ish, I went to take it off my hotplate, having decided to give up, and dropped the 50mL beaker on the hotplate, shattering it and spilling a lot of almost boiling liquid on the ground and on the hotplate.




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[*] posted on 17-12-2014 at 20:26


Quote: Originally posted by No Tears Only Dreams Now  
This just doesn't make any sense! Do you recall when earlier I said I was going to make some ferrous sulfate solution by displacing the copper from copper sulfate?

I put an excess of steel wool into some copper sulfate solution, added just a bit of HCl to get the reaction started, and was left with a very light green solution. At this point the solution really shouldn't be more than a tiny bit below pH 7. So I boiled that solution down to about 1/3 of the original volume, during which no color change occurred except a concentration of the green color. An hour in my freezer, and I got a nice little crop of fluffy FeSO4 crystals; EVERYTHING was exposed to the air during this time; there wasn't even a lid on the container in the freezer. I don't understand how one person can have such a negative experience with this compound when mine is perfectly content to remain unoxidized.

I know exactly what you mean! One thing though is that it does seem like it oxidizes much more rapidly when it is wet. From my experience with iron(II) sulfate, you need to dry it as quickly as possible once you get your crystals. After that, letting them sit open to the air is no problem. I've had some open to the air for months with no signs of oxidation whatsoever. Solutions of it however will go brown within hours. The silver lining though, is that if you let a solution evaporate, while the solution does get oxidized, large, well-formed crystals of iron(II) sulfate will crystallize on the bottom of the container. Then you can remove the crystals, rinse them with water to clean them (they clean up very nicely) and then once no more will crystallize, filter the solution, separating the iron(III) sulfate and oxide. The oxide can then be dried, and the sulfate crystallized, and you have three decently pure compounds from one vessel. I think I will make a YouTube video of this procedure at some point.



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[*] posted on 17-12-2014 at 22:49


Quote: Originally posted by DraconicAcid  
Quote: Originally posted by DrMario  
I thought a sufficiently acidic environment should prevent this from happening.


It happens faster under basic conditions, but it will still happen in acidic ones. Keep the air out.

Oh, and you didn't filtrate the solution- you filtered it. The solution you got afterwards was the filtrate.


I guess it's the trappings of my Italian being my second mother tongue - it interferes with English sometimes.
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[*] posted on 17-12-2014 at 23:10


I have one nagging question that has been bothering me since the first time I read the advice to add H2SO4: wouldn't an excess of sulphuric acid, added to a solution that contains a mixture of Fe(II) and Fe(III) sulphate effectively "push" the ratio towards higher Fe(III) sulphate content?
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[*] posted on 13-1-2015 at 12:06


And here it is, ferrous sulfate crystals:





It was easier than I thought... once I actually tried cooling the solution of iron(II) sulfate and H2SO4.
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[*] posted on 13-1-2015 at 12:20


They look really pretty, hopefully they stay similar to that.



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[*] posted on 13-1-2015 at 13:06


It's about time! I should be preparing quite a bit soon by the copper sulfate/steel wool method, if mine goes disastrously for once, I'll know which thread to come to...



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[*] posted on 13-1-2015 at 15:31


Quote: Originally posted by The Volatile Chemist  
They look really pretty, hopefully they stay similar to that.


The truth is, I prepared this batch three weeks ago. It was really very cold outside, so I used that instead of the fridge :)
The crystals in the bottle look more-or-less the same, but I don't vouch that I managed to remove all the H2SO4 from them, so the acid might be protecting the ferrous sulfate from oxidizing to ferric sulfate.

Maybe I'll take a photo of the bottle a couple of weeks from now and we can all compare the colour. A yellowing would indicate oxidation.
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[*] posted on 14-1-2015 at 09:12


Quote: Originally posted by DrMario  
Quote: Originally posted by The Volatile Chemist  
They look really pretty, hopefully they stay similar to that.


The truth is, I prepared this batch three weeks ago. It was really very cold outside, so I used that instead of the fridge :)
The crystals in the bottle look more-or-less the same, but I don't vouch that I managed to remove all the H2SO4 from them, so the acid might be protecting the ferrous sulfate from oxidizing to ferric sulfate.

Maybe I'll take a photo of the bottle a couple of weeks from now and we can all compare the colour. A yellowing would indicate oxidation.

A bottle I ordered about 3 months ago has really oxidized, I'm kinds annoyed. I guess storing it in a little bit of residual H2SO4 would help.




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