NexusDNA
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Ferricyanide stuff
Hello! I have some potassium ferricyanide lying about. Are there any twinkly experiments/syntheses you recommend? I've already done "printing" with
prussian blue.
On another note, i wanted to reduce some of the ferricyanide to ferrocyanide. I know that latter is oxidized by chlorine gas to ferricyanide, so I
have two questions:
1. How does the reaction with chlorine take place without changing the Fe-CN bonds?
2. How could I reverse it to make ferrocyanide?
Thanks! 
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woelen
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1) The reaction is a simple electron transfer reaction. There is no need for structural change. The electron will pass from the ferrous core through
one of the CN(-) ligands and rearrangement of charge makes it a ferricyanide ion.
2) Many reductors are capable of transforming it to ferrocyanide (e.g. SO2, metal powders), but isolating the ferrocyanide will not be easy. I would
try it with SO2. Bubble the SO2 through a solution of K3Fe(CN)6. It will be oxidized to H2SO4. The liquid will become acidic. In this way you
introduce a minimum of foreign ions from which the material has to be separated.
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sasan
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Last night I tried to make some potassium nitroprusside::
5 KCN + 2 FeSO4 + KNO2 + H2O ==>potassium nitroprsside+ 2Fe(OH)2 + 2K2SO4
I dont know if it is right or not,this method is from iron.atomistry.com
Nitroprusside is reddish orange but after filtaration the precipitates I got a dark greenish blue precipitate(comparing to the color of iron
hydroxides) and a light yellowish solution.is this potassium nitroprusside solution or pottassium ferrocyanide?? The ferrocyanide color is light
yellow.but ntroprusside is reddish orange.please post your suggestions.
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bismuthate
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Add it to copper (II) solution to get a red precipitate. Also woelen, wouldn't H2SO4 react with ferrocyanide and in a dangerous way at that?
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blogfast25
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Quote: Originally posted by bismuthate  | | Add it to copper (II) solution to get a red precipitate. Also woelen, wouldn't H2SO4 react with ferrocyanide and in a dangerous way at that?
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If you're hinting at hydrogen cyanide, it would require high concentrations of acid to liberate that gas from ferro/ferricyanides because these are
very strong complexes (very high complexation constant). For instance ferricyanide (more correctly hexacyano ferrate (III)) does not show typical
reactions of the ferric ion: add some ammonia to the solution and no ferric hydroxide precipitates. Going by the extraordinary insolubility of ferric
hydroxide that's a remarkable testament to the complex's strength.
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NexusDNA
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Thanks for the replies. So the suggestion is to do it with a substance that will transfer electrons to the iron without polluting the solution with
ions.
With SO2, the stoichiometry will be 1:2 SO2 to K3Fe(CN)6, right? Should I do it with a slight excess of SO2? H2O2 will help? I'll try it in small
scale when I have a generator.
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blogfast25
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How will it help?
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Brain&Force
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I'm just spitballing here, but would potassium sulfite work as a reducer?
At the end of the day, simulating atoms doesn't beat working with the real things...
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woelen
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@NexusDNA: I would use excess of SO2. The amount which is not used can easily be driven off by heating the solution for a while.
@Brain&Force: Potassium sulfite as a reductor may work as well. You should indeed use potassium sulfite and not sodium sulfite in order to avoid
the introduction of new ions, from which the wanted K4Fe(CN)6 must be separated. Sulfite ion is less reactive than SO2, so you should try this
reaction before mixing large amounts of chemicals, but I can imagine that it will work, especially if helped a little bit by heating the solution. You
can see whether it works or not by fading of the color of the solution of K3Fe(CN)6 from deep yellow to pale yellow.
With K2SO3 you get just the right amount of potassium ions in the solution. The solution will become weakly acidic. Again, use a slight excess of
K2SO3. K2SO3 may be hard to get. In that case, use K2S2O5 (potassium metabisulfite), which is easy to find in brewery and wine making shops.
[Edited on 26-5-14 by woelen]
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NexusDNA
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I really don't remember how I got to this conclusion. I guess alcohol doesn't help calculating redox. 
As I don't have access to potassium metabisulfite, I'll be using the sodium analogue + HCl as a SO2 generator. It should work just fine!
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The Volatile Chemist
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Does anyone know of any interesting reactions with hexacyanoferrate (II) and (III)? I have way too much of both, but I've already produced a lot of
hexacyanoferrate salts, anything else I can do with them?
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gdflp
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If your interested in a synthesis, sodium nitroprusside is an interesting compound. There are two routes, one with nitric acid and sodium carbonate,
the other uses barium chloride, sodium chloride(If using potassium salt), sodium nitrite, and carbon dioxide. Personally I prefer the first one, much
easier and bubbling CO2 through the mixture for hours is a pain.
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NexusDNA
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| Quote: Originally posted by The Volatile Chemist | | Does anyone know of any interesting reactions with hexacyanoferrate (II) and (III)? I have way too much of both, but I've already produced a lot of
hexacyanoferrate salts, anything else I can do with them? |
As I already commented, "printing" with prussian blue is nice and relatively safe. You'll only need a Fe(III) salt, oxalic acid and K3Fe(CN)6.
[Fe(C2O4)3]3- →hv→ [Fe(C2O4)2]2- + 2 CO2
This reaction only happens in the presence of light, so if you use a negative you can "print" the photo onto paper or even a shirt (I have yet to try
this last one). This paper shows some of the idea: http://firstyear.chem.usyd.edu.au/LabManual/E02.pdf
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The Volatile Chemist
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Thanks 
I'd already tried it, but I enjoy the reaction.
It's so messy though...
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