Ferric Ammonium Citrate (green) solubility

Discussion in 'Alternative Processes' started by Anon Ymous, Jun 16, 2017.

  1. Anon Ymous

    Anon Ymous Member

    Messages:
    1,923
    Joined:
    Feb 7, 2008
    Location:
    Greece
    Shooter:
    35mm
    Groups:
    Hello...

    As the title says, I'd like to know just how soluble it is, not just "very soluble in water". You see, I have a probably 50% w/v solution and I'd like to crystallise the salt. Refrigerating it for 8 hours didn't do the trick. Now, perhaps I should concentrate it more, or add a crystal in it, to act as a nucleation site. Anyway, any help would be welcome.

    Thanks in advance.
     
  2. bernard_L

    bernard_L Member

    Messages:
    553
    Joined:
    Feb 17, 2008
    Shooter:
    35mm
    You need to get rid of the water.
    • Leave in an open tray, and wait... a certain time
    • Boil the solution. Risky: might alter the sought-after molecule.
    • Pump to a moderate vacuum the air above the solution, maybe with moderate heat. Water molecules will be pumped away, and, if the vacuum is good enough, the solution might boil at room temperature.
    Hopefully a Real Chemist will chime in.
     
  3. pdeeh

    pdeeh Member

    Messages:
    4,647
    Joined:
    Jun 8, 2012
    Location:
    UK
    Shooter:
    Multi Format
  4. OP
    OP
    Anon Ymous

    Anon Ymous Member

    Messages:
    1,923
    Joined:
    Feb 7, 2008
    Location:
    Greece
    Shooter:
    35mm
    Groups:
    Oops, somehow I missed it. 120% is way too much compared to 50%. :pouty:

    Well, it seems evaporation is inevitable. Option 1 is boring. Option 3 is not really an option as I don't have a vacuum pump. It would be awesome though, as it would enable boiling at much lower temperatures. I might buy an aspirator pump one day, these are useful if you do things like that. So, that leaves option 2 only. Actually, I reached the 50% w/v point with light boiling. It's a little tedious, because if the solution is left to boil unattended, it has the tendency to stay calm and suddenly splash a lot. You either need to add some boiling chips, or continuously stir with a rod. Oh well...
     
  5. pdeeh

    pdeeh Member

    Messages:
    4,647
    Joined:
    Jun 8, 2012
    Location:
    UK
    Shooter:
    Multi Format
    Google is now so intent on giving you answers to questions *it* thinks you have asked and then putting ads in front of you to suit those answers, it has become increasingly hard to get the answers to questions you *actually* ask.

    TIP: On the google results page, click "Tools", which should show a submenu including the option "All Results".
    "All Results" has a drop down menu offering the option "Verbatim" - select this.
    Then google will show results of all and only what you have entered as the query, instead of it's (often useless) interpretation of your query.

    TIP FOR BROWSER GEEKS: You can set your search results to be always "Verbatim" by adding "&tbs:li=1" to end of your search string
    (i'm not going to provide a tutorial on how to setup your browser search engine preferences to do that, no :smile:)
     
  6. OP
    OP
    Anon Ymous

    Anon Ymous Member

    Messages:
    1,923
    Joined:
    Feb 7, 2008
    Location:
    Greece
    Shooter:
    35mm
    Groups:
    Indeed, it is! Sometimes the results are so hopelessly irrelevant that it gets annoying. I remember searching for development times across the web for a specific film in Perceptol. I got very few relevant results and far too many completely irrelevant ones where "Rodinal" was the highlighted keyword! :mad:

    And this tip makes things sane again, many thanks, I had missed it.
     
  7. Ian Leake

    Ian Leake Subscriber

    Messages:
    1,473
    Joined:
    Mar 25, 2005
    Location:
    Switzerland
    Shooter:
    8x10 Format
    Warming gently will greatly speed up evaporation
     
  8. OP
    OP
    Anon Ymous

    Anon Ymous Member

    Messages:
    1,923
    Joined:
    Feb 7, 2008
    Location:
    Greece
    Shooter:
    35mm
    Groups:
    I've already evaporated much of the excess water. The solution is now a thick syrup, but it's hard to estimate the volume (and concentration), as it would result in great loss of product. I've put it in the fridge, but I'm not very sure I'll get any crystals.
     
  9. nmp

    nmp Member

    Messages:
    259
    Joined:
    Jan 20, 2005
    Shooter:
    35mm
    I think this might work for you. Find a non-solvent for FAC that is miscible in water, like alcohols, acetone etc. Add to precipitate. Do a test with a small amount to make sure and get an idea of how much to add. Precipitates can be re-dissolved in water to the required concentration for re-crystallization. Or you can add the non-solvent to the point of precipitation and let it recrystallize in the refrigerator.
     
  10. OP
    OP
    Anon Ymous

    Anon Ymous Member

    Messages:
    1,923
    Joined:
    Feb 7, 2008
    Location:
    Greece
    Shooter:
    35mm
    Groups:
    I've tried to get some precipitate from the syrup (a tiny bit of it) using 95% ethanol. It didn't even seen to thin the syrup. :sad:
     
  11. Ian Leake

    Ian Leake Subscriber

    Messages:
    1,473
    Joined:
    Mar 25, 2005
    Location:
    Switzerland
    Shooter:
    8x10 Format
    If you've still got a 'syrup' then evaporation isn't completed.

    Typically you would heat the solution in an oven until all the solvent (in this case water) has evaporated. That will leave just the solute (in this case ammonium ferric citrate).

    Ammonium ferric citrate is hygroscopic, which means it easily absorbs water from the atmosphere. You may find that at room temperatures the waters never fully evaporates.

    Why are you putting this in a fridge? I've not measured humidity inside a fridge, but I expect it's quite high, which would make it a bad place to separate a hygroscopic substance.
     
  12. nmp

    nmp Member

    Messages:
    259
    Joined:
    Jan 20, 2005
    Shooter:
    35mm
    May be it requires a large excess of the alcohol. I wonder if you can put this alcohol(add as mush as you can)/water/FAC solution in the freezer. If the freezing point of water is suppressed enough, it will not freeze, but FAC may.
     
  13. OP
    OP
    Anon Ymous

    Anon Ymous Member

    Messages:
    1,923
    Joined:
    Feb 7, 2008
    Location:
    Greece
    Shooter:
    35mm
    Groups:
    It didn't start as a powder, or crystals, I synthesized fact last night and need to somehow precipitate it out of solution. Synthesis was quite easy, but crystalisation seems quite hard. It now sits in the freezer and there might be some crystals at some point, but I don't really hold my breath.
     
  14. nmp

    nmp Member

    Messages:
    259
    Joined:
    Jan 20, 2005
    Shooter:
    35mm
    what was your synthetic route, if you don't mind telling: Ferric chloride + KOH to Fe(OH)3 plus citric + ammonia to FAC? If so, if I am not missing something, you would end up with 100% FAC solution (provided the hydroxide was cleaned up good.) Why can't you simply use this solution for your alt process, rather than trying to obtain in the crystalline form.

    Just curious....
     
  15. OP
    OP
    Anon Ymous

    Anon Ymous Member

    Messages:
    1,923
    Joined:
    Feb 7, 2008
    Location:
    Greece
    Shooter:
    35mm
    Groups:
    The synthetic route was almost as you said. The two differences were the use of Sodium Carbonate instead of KOH and Ammonium Bicarbonate instead of ammonia. The Fe(OH)3 was washed, but there must have been some Na2CO3 left in there, because it fizzed a tiny bit after adding the citric acid. Anyway, in the end I got a nice, clear, dark green solution, containing about 35g of FAC. Now, AFAIK, such solutions don't have a long storage life and things will grow in there, hence my preference for crystals as a product.
     
  16. nmp

    nmp Member

    Messages:
    259
    Joined:
    Jan 20, 2005
    Shooter:
    35mm
    Got it. Wonderful. Hope you are successful. Purification of the product is the underappreciated skill in chemistry. FAC is relatively cheap, I had been thinking about making ferric oxalate which is significantly more expensive, but from the perspective of synthesis pretty similar. Wonder why.
     
  17. OP
    OP
    Anon Ymous

    Anon Ymous Member

    Messages:
    1,923
    Joined:
    Feb 7, 2008
    Location:
    Greece
    Shooter:
    35mm
    Groups:
    Yes, it's fairly cheap and readily available, but where's the fun in just buying stuff? :D

    Meanwhile, I found the relevant patent US2644828, which mentions that crystallisation of FAC is quite difficult (or was back in the 1940s) and the usual product was either scales, or granules and came after evaporation to dryness. Addition order of the reagents is supposed to be critical, among other factors, and obtaining crystals from the thick, syrupy solutions takes place after several days in an "ice chest", after being helped by either adding some crystals, or scratching the bottom of the glass container. Obviously, these are nucleation sites, without which things would be far slower, if they'd happen at all.
     
  18. Herzeleid

    Herzeleid Member

    Messages:
    243
    Joined:
    Oct 31, 2008
    Location:
    Ankara/Turkey
    Shooter:
    Multi Format
    Groups:
    You can try to make primitive DIY desiccator to dry the syrupy FAC.
    I also made FAC just to see if I can make it, but I left it in solution. I expected the crystallization would be problematic.
    I dried ammonium ferric oxalate and ferric oxalate with ease using simple DIY desiccator.
    I would use sodium hydroxide to dry out the chemicals, It is quite easy to obtain. Leave it for a week sometimes a few days is enough.


    Regards
    Serdar
     
  19. OP
    OP
    Anon Ymous

    Anon Ymous Member

    Messages:
    1,923
    Joined:
    Feb 7, 2008
    Location:
    Greece
    Shooter:
    35mm
    Groups:
    Serdar, the DIY desiccator approach is something that I've considered, I already have about 1kg of NaOH. Actually, I've even watched this video in the past. :smile: But as you also did, I'll probably thin my FAC syrup to a reasonable concentration, store it in the fridge and use it as is. After a bit more searching in the forum, it seems that any mould formed can be filtered out and the rest of the solution can be used without any problems. It is also good to know that this DIY desiccator helped drying oxalate salts. Anyway, now I need to somehow make some digital negatives in order to make my first cyanotypes...

    Many thanks for the tips.