lazaruz
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Brown Iron (II) sulfate solution
I'm trying to understand why my solution of Iron (II) sulfate dissolved in water turns brown.
What I'm attempting is recrystallization of Iron (II) sulfate moss killer to purify it, but I have to deal with a lot of brown sludge forming on the
bottom.
There are nice green crystals forming but it always has this brown on them.
Is this caused by oxidation and is it Iron oxide that is formed?
Is it because I heat the solution too much? It seems to get worse with heat.
Is there any way to prevent this?
I'm very new to this so any help would be greatly appreciated.
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Lefaucheux10
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it is irone oxyde
you can boil it with H2SO4 and metallic iron it will reduce all your stuff in FeSO4
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NEMO-Chemistry
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Iron II Sulphatenear the bottom where it says reactions. HTH
[Edited on 2-9-2016 by NEMO-Chemistry]
No idea why the other link didnt work
[Edited on 2-9-2016 by NEMO-Chemistry]
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Aqua-regia
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Brown color means you have Fe3+ ions. (FeSO4 very sensitive for oxidation. If the deionised water for dissolving it not boiled off befor you do
the dissolving, you get also oxidation.
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lazaruz
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Thank you, that helped me to understand the process a bit more 
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blogfast25
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Quote: Originally posted by lazaruz  | I'm trying to understand why my solution of Iron (II) sulfate dissolved in water turns brown.
What I'm attempting is recrystallization of Iron (II) sulfate moss killer to purify it, but I have to deal with a lot of brown sludge forming on the
bottom.
There are nice green crystals forming but it always has this brown on them.
Is this caused by oxidation and is it Iron oxide that is formed?
Is it because I heat the solution too much? It seems to get worse with heat.
Is there any way to prevent this?
I'm very new to this so any help would be greatly appreciated. |
ALWAYS include some free H2SO4 if you want to recrystallise FeSO4.
The oxidation reaction:
2 Fe2+(aq) + 1/2 O2(g) + H2O(l) === > 2 Fe(OH)2+(aq)
... proceeds much faster in neutral/alkaline conditions than in acid conditions.
[Edited on 2-9-2016 by blogfast25]
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lazaruz
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| Quote: Originally posted by blogfast25 |
ALWAYS include some free H2SO4 if you want to recrystallise FeSO4.
The oxidation reaction:
2 Fe2+(aq) + 1/2 O2(g) + H2O(l) === > 2 Fe(OH)2+(aq)
... proceeds much faster in neutral/alkaline conditions than in acid conditions.
[Edited on 2-9-2016 by blogfast25] |
So without H2SO4 it's not really possible to get a good recrystallization? The thing is, I live in Sweden and we are not allowed
to buy that without a permit.
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blogfast25
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| Quote: Originally posted by lazaruz |
So without H2SO4 it's not really possible to get a good recrystallization? The thing is, I live in Sweden and we are not allowed
to buy that without a permit. |
It's difficult to get a nice, green oxidation-free product, yes.
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zwt
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| Quote: Originally posted by lazaruz | | So without H2SO4 it's not really possible to get a good recrystallization? The thing is, I live in Sweden and we are not allowed
to buy that without a permit. |
You might be able to acidify your iron(II) sulfate through brief electrolysis
at low current density with inert electrodes. This will convert some of the iron(II) sulfate to sulfuric acid, with the iron leaving solution as the
metal (which, if done properly, will adhere to the cathode and be cathodically protected from redissolving). Of course, you'll have to add more
iron(II) sulfate to make up for what is lost.
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lazaruz
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| Quote: Originally posted by zwt | | Quote: Originally posted by lazaruz | | So without H2SO4 it's not really possible to get a good recrystallization? The thing is, I live in Sweden and we are not allowed
to buy that without a permit. |
You might be able to acidify your iron(II) sulfate through brief electrolysis
at low current density with inert electrodes. This will convert some of the iron(II) sulfate to sulfuric acid, with the iron leaving solution as the
metal (which, if done properly, will adhere to the cathode and be cathodically protected from redissolving). Of course, you'll have to add more
iron(II) sulfate to make up for what is lost. |
That sounds like a nice experiment to try, thanks!
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