Lion850
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Report on making Ammonium pentachloroferrate
In the ongoing quest to make pure red colored salts I found the synthesis of ammonium pentachloroferrate on a crystal growing website:
https://en.crystalls.info/Ammonium_pentachloroferrate(III)
On the crystal site the color is described as red-brown but on atomistry here
http://iron.atomistry.com/pentachlorferrates.html
it is said to be garnet red. Expected reaction is:
2NH4Cl + FeCl3.6H2O = (NH4)2[FeCl5(H2O)] + 5H2O
Procedure:
- 10g NH4Cl dissolved in 20g water in a small beaker.
- 25.2g FeCl3.6H2O dissolved in 30g water in a small beaker.
- Mix hot solutions and fast stirring.
- Solution got darker as reaction progressed, finally being very dark brown-red. After mixing everything the volume was approximately 60ml with no
solids observed.
- Boil down from 60 to just under 40ml, at which point red crystals quickly started to fall out of solution. Photo below.
- Remove stir bar and leave standing to cool down slowly with the hot plate.
- When I returned after some 4 hours it was at room temp and there was an abundance of crystals. The crystals were scratched out and squeezed between
2 filter papers which in turn was between layers of paper towel. This got the crystals reasonably dry. At this point the recovery was 12.7g. See photo
below.
- Left the crystals out in a crucible overnight to see if they naturally dry more. However the next morning they were noticeably more wet and the
weight increased from 12.7 to 13.6g. Afterwards I red on a crystal growing report that this compound is slightly hygroscopic.
- Into desiccator under high vacuum and over NaOH for 24 hours. After 24 hours the seemed quite dry, and the weight reduced from 13.6 to 12.4g.
Final product bottled, see photo below. I await with interest to see how long lasting the color is.
Close-up of the product in the bottle.
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woelen
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This really is interesting. I did not know of this compound. Maybe add a few drops of conc. HCl to the mix before boiling it down? Iron(III) has a
strong tendency to hydrolyse and form insoluble hydroxo-species, which may contaminate the material and make it less red. but more brown. But your
result looks quite good.
Is this material hygroscopic? Ferric chloride is.
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Lion850
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Hi Woelen yes it is slightly hygroscopic. As I mentioned in the post I left it out overnight to see if it would dry naturally but it got slightly
wetter and gained a gram of weight. Thus I had to dry it in a desiccator for 24 hrs.
The compound being slightly hygroscopic was also mentioned by one crystal grower online. He also says the color faded after a week, I will see what
happens to mine!
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MidLifeChemist
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I also repeated this experiment over the weekend. I combined proper ratios of FeCl3 and NH4Cl, and brought the solution to a slight boil. I observed
similar color changes as Lion850 observed.
The water level was going down in the beaker slowly, so I took a short walk. When I returned, the beaker was hot & bone dry, and the assumed
Ammonium Pentachloroferrate was also hot and dry.
In retrospect, this may not have been a bad thing, as I was able to scrape it all out, and I did not have to filter. Mine is a nice red-orange color,
but mine does not seem to be hygroscopic at all. It may have impurities of FeCl3 or NH4Cl but at the moment I'm not too concerned about it.
I'll post some photos tomorrow.
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woelen
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I am afraid that yours contains a lot of oxide/hydroxide. I am quite sure that by overheating this compound you lose HCl besides H2O and you get
oxide/hydroxide contamination. Such material usually is not hygroscopic and that may explain the difference with other observations.
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MidLifeChemist
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Quote: Originally posted by woelen  | | I am afraid that yours contains a lot of oxide/hydroxide. I am quite sure that by overheating this compound you lose HCl besides H2O and you get
oxide/hydroxide contamination. Such material usually is not hygroscopic and that may explain the difference with other observations.
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Thanks for the feedback, much appreciated. Well this is interesting. Since i have more FeCL3 and NH4Cl, I can easily test this by producing more and
not overheating it. Stay tuned!
>> I am quite sure that by overheating this compound you lose HCl
Just to clarify, are you suggesting that all or a good portion of the NH4FeCl5 was broken down?
[Edited on 28-10-2020 by MidLifeChemist]
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woelen
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No, not all of it, but more than you would want.
In general, if you heat hydrated transition metal salts, then they tend to lose acid besides water. With some metal salts the loss of acid is really
severe, so much that only the hydroxide/oxide remains behind:
2 FeCl3.6H2O -->(heating)--> Fe(OH)3 + 3H2O + 3HCl, stronger heating leads to Fe2O3.
With others, there is a little loss:
CuCl2.2H2O -->(heating)--> CuCl2 + 2 H2O (main reaction)
CuCl2.2H2O -->(heating)--> Cu(OH)Cl + HCl + H2O (side reaction, few percents, depending on strength of heating)
You can check for acid loss by adding some of the heated anhydrous compound to water. The material will dissolve again, but if the solution is turbid,
then some oxide/hydroxide is formed. If there is complete loss of the anion and all is converted to oxide/hydroxide, then the material will not
dissolve in water anymore.
The same can also happen with bromides, nitrates, acetates and many other anions. Sulfates and phosphates usually are somewhat less prone to loss of
acid. Probably that is due to the high boiling point of the free acids.
[Edited on 28-10-20 by woelen]
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MidLifeChemist
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I did a second run of the Ammonium Pentachloroferrate synthesis. This time I did not let the beaker boil dry, but I did boil it down to less than half
the original volume. Again, the reaction proceeded exactly as Lion850 described, and a nice amount of (NH4)2FeCl5 crystallized out. I cooled the
solution, and filtered via vacuum filtration with my 110mm buchner funnel and hand pump until the crystals were as dry as possible.
They were a beautiful red-orange color, similar to what Lion850 posted. I spread them onto a watch glass and let them dry even further overnight. they
have lost 15% of their mass in the last 16 hours. The product of the first run was also reddish-orange, but the first run was more orange and this run
is more red. The feel / consistency of the crystals is similar - although the results of my second run look more stunning.
Like I mentioned, after filtration was done, I weighed the crystals, and then weighed them 8 hours and 16 hours later. They have been slowly losing
mass due to further water evaporation as they were not completely dry from the vacuum filtration. I will continue to monitor their weight over the
next 24 hours, but my first impression is that they do not strike me as a particularly hygroscopic compound. I will post further results tomorrow.
I would be interested to find out if there are any other pentachloroferrate compounds to create. If anyone has any ideas let me know, otherwise this
salt mayjust sit in a HDPE bottle - although I'm sure I'll think of some reaction to try.
[Edited on 1-11-2020 by MidLifeChemist]
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Lion850
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Looks good mate! I found it to be very slightly hygroscopic, but it’s been very humid here. Or maybe there is a bit of ferric chloride left in mine.
So far my color has not changed; online one crystal grower reported the color fading after a week.
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Lion850
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Look at this on Atomistry;
http://iron.atomistry.com/pentachlorferrates.html
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MidLifeChemist
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| Quote: Originally posted by Lion850 | | Looks good mate! I found it to be very slightly hygroscopic, but it’s been very humid here. Or maybe there is a bit of ferric chloride left in mine.
So far my color has not changed; online one crystal grower reported the color fading after a week. |
Thanks for the link to Atomistry. Not much info there imho, maybe I'll try reacting it with some different salts / reagents.
Well the weight has been stable over the last 24 hours, and the color hasn't faded at all. Still a really nice red-orange.
Do you have any plans for yours?
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Lion850
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No plans just add to the collection of coloured salts 
I would like to try this with cesium but the only cesium salts I found available locally are very expensive.
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