Sciencemadness Discussion Board

Crystallization of Iron(II) sulfate

Alchemic - 23-3-2016 at 05:22

Hi!
I have a mixed solution of Sodium Sulfate and Iron sulfate.

It to would be nice to separate them and to crystalize just an Iron sulfate.
I had a look at solubility and unfortunattely it is very close for both instances.

Is there any ideas how to crystalise just an Iron sulfate?

Hegi - 23-3-2016 at 06:26

Quote: Originally posted by Alchemic  
Hi!
I have a mixed solution of Sodium Sulfate and Iron sulfate.

It to would be nice to separate them and to crystalize just an Iron sulfate.
I had a look at solubility and unfortunattely it is very close for both instances.

Is there any ideas how to crystalise just an Iron sulfate?


OK. I would try........ Add an excess of sodium hydroxide solution to your mixture. The precipitate of Iron(II) hydroxide will form. Filter it off as quickly as you can and wash it with huge amount of water to get a rid of sodium sulfate and hydroxide. Transfer the precipitate to the beaker and add sulfuric acid to dissolve it (in excess and also some iron nails to reduce oxidized iron atoms). Should work.

annaandherdad - 23-3-2016 at 06:43

For fractional crystallization, you need to pay attention to the fraction of each substance present, in addition to the solubilities. For example, in sea water the calcium sulfate crystallizes first (low solubility, low concentration), then sodium chloride (moderate solubility, less than that of some other ingredients, but present at 90% mass fraction). Then at a later point you get magnesium chloride and other things, that you can separate mechanically because the crystal structures are so different. But to get pure compounds requires multiple crystallizations and it involves some loss.

So, in your case, what are the percentages of sodium sulfate and iron II sulfate? Also note that the crystals of each are of different colors, and it might be possible to separate them mechanically.

Alchemic - 23-3-2016 at 10:10

Quote: Originally posted by Hegi  
Quote: Originally posted by Alchemic  
Hi!
I have a mixed solution of Sodium Sulfate and Iron sulfate.

It to would be nice to separate them and to crystalize just an Iron sulfate.
I had a look at solubility and unfortunattely it is very close for both instances.

Is there any ideas how to crystalise just an Iron sulfate?


OK. I would try........ Add an excess of sodium hydroxide solution to your mixture. The precipitate of Iron(II) hydroxide will form. Filter it off as quickly as you can and wash it with huge amount of water to get a rid of sodium sulfate and hydroxide. Transfer the precipitate to the beaker and add sulfuric acid to dissolve it (in excess and also some iron nails to reduce oxidized iron atoms). Should work.

Thanks for the "recipie" but makes not too much sense - it would be same thing if to discard the whole solution and to start etching rusty nails.... it would save at least one reagent (base) and less acid will be used

DraconicAcid - 23-3-2016 at 10:37

Fractional crystallization assumes that a mixed salt such as Na2Fe(SO4)2 doesn't form. That might not be a good assumption.

annaandherdad - 23-3-2016 at 12:34

Yes, that's true, and I certainly don't know if it does, but if you just evaporate some and find crystals of two different colors, it probably means that you have separated sodium and ferrous sulfates.

Hegi - 25-3-2016 at 10:42

Quote: Originally posted by Alchemic  
Quote: Originally posted by Hegi  
Quote: Originally posted by Alchemic  
Hi!
I have a mixed solution of Sodium Sulfate and Iron sulfate.

It to would be nice to separate them and to crystalize just an Iron sulfate.
I had a look at solubility and unfortunattely it is very close for both instances.

Is there any ideas how to crystalise just an Iron sulfate?


OK. I would try........ Add an excess of sodium hydroxide solution to your mixture. The precipitate of Iron(II) hydroxide will form. Filter it off as quickly as you can and wash it with huge amount of water to get a rid of sodium sulfate and hydroxide. Transfer the precipitate to the beaker and add sulfuric acid to dissolve it (in excess and also some iron nails to reduce oxidized iron atoms). Should work.

Thanks for the "recipie" but makes not too much sense - it would be same thing if to discard the whole solution and to start etching rusty nails.... it would save at least one reagent (base) and less acid will be used


You asked for the method ;) But anyway, you are right, discard it and make a new or buy one.

pesco - 30-3-2016 at 10:35

Quote: Originally posted by Alchemic  
Hi!
I have a mixed solution of Sodium Sulfate and Iron sulfate.

It to would be nice to separate them and to crystalize just an Iron sulfate.
I had a look at solubility and unfortunattely it is very close for both instances.

Is there any ideas how to crystalise just an Iron sulfate?


Direct separation is impossible, but you can get something out of it anyway.

Boil the mixture.
To oxidize iron(II) sulphate to iron(III) sulphate add some H2SO4 (you'll recover it later) and H2O2. If you don't want to use peroxide aerating hot solution should work as well.
Insoluble jarosite will drop according to reaction :

Na2SO4 + 3 Fe2(SO4)3 +12 H2O = 2 NaFe3(SO4)2(OH)6 + 6 H2SO4

Make sure there is enough sodium sulphate in the mixture or not all Iron would drop.

Once that done, filter off jarosite and you have mix of very useful chemicals -> Na2SO4 and H2SO4.
Once separated the later you can use to dissolve some rusty nails.


Some losses are present in form of jarosite, but better that than discarding the whole mess.


Regards

[Edited on 30-3-2016 by pesco]

[Edited on 30-3-2016 by pesco]

[Edited on 30-3-2016 by pesco]

crystal grower - 30-3-2016 at 11:55

Do not forget na2so4 in acidic enviroment ----> NaHSO4. :D.

pesco - 30-3-2016 at 12:14

Well pointed out grower.