NexusDNA
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Potassium Ferricyanide crystals
Hello everyone!
This is my first post, though I've been taking a look at the forum for quite a bit, and I must say that I'm really impressed with all the top notch
info you have been discussing. So, as an amateur inexperienced highschool chemistry/electronics/science enthusiast, this forum is really exhilarating!
I have started gathering glassware and unharmful reagents, and also making some easy projects. Recently i've grown blue copper sulfate crystals and
yeah, they were really better than i expected! So i did a bit of research and found that red crystals could be grown out of potassium ferricyanide.
All right, i bought the ferricyanide from a chemistry supplier close to my location and all went fine. Thing is, when I first opened the bottle i
noticed a very strong smell, and closed it up right away. I may be wrong, but, shouldn't it be odorless? I'm afraid it could be HCN! Well, i'm not
dead by now anyway, haha. It has closed up ever since.
The bottle said it contained 99% of potassium ferricyanide and 1% chlorate (maybe this is the cause?). I'd like some advice from you please.
Thanks!
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Random
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Can you describe the strong smell?
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NexusDNA
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Well, I'd say it was heavy and a bit bitter, but not acid.
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Random
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Not being an expert in this I would wait for another member since cyanide is nothing to take lightly. As people often describe, HCN would have fruity
almondish odor. Bitter but not acidic could be maybe a description for it too since not everyone smells it the same.
Really, just wait for few other opinions to be on the safe side.
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hyfalcon
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Since oral LD50 values for HCN are 3-4mg per kg of body weight, I doubt you can get a lethal dose from some vapors coming out of a jar of potassium
ferricyanide.
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Random
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Quote: Originally posted by hyfalcon  | | Since oral LD50 values for HCN are 3-4mg per kg of body weight, I doubt you can get a lethal dose from some vapors coming out of a jar of potassium
ferricyanide. |
It's still a considerable amount especially if he has a lower bodyweight. Better question is, if the gas is HCN, there may be cyanide impurity.
I wonder if there are test strips for it, like lead strips for H2S.
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NexusDNA
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A test strip would be ideal. I also noticed that most of the content inside the bottle formed a big chunk, not sure if somehow related. What would
cause the ferricyanide to decompose to HCN? Overheating? I doubt cyanide impurity would pass purity tests, as it is a major concern to heath and
ferricyanide it is not a controlled reagent.
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Random
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Here it says alkaline picrate test strip can be used. You probably don't have it on hand though..
http://www.ajol.info/index.php/br/article/view/56582
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Galinstan
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The clumping in the bottle is probably due to the fact that chlorate is hygroscopic and therefore will absorb water from the air and cause the powders
to clump so probably has nothing to do with the smell, unless there's something in there that reacts with the water to form a mild acid and somehow
create free HCN although ferricyanide is quite stable, Puzzling 
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hyfalcon
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Possibly some Chloric acid formation from the chlorate and moisture it's picked up could possibly form the HCN. I still don't think it would be in a
concentration to be worried about. I don't know what the solubility curve in reference to temperature is on the ferricyanide, but you should be able
to separate the KClO3 by dissolving in a minimum of water and the cooling it down close to 00C. The KClO3 should
drop out at that point.
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TheChemiKid
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| Quote: Originally posted by Random | | Not being an expert in this I would wait for another member since cyanide is nothing to take lightly. As people often describe, HCN would have fruity
almondish odor. |
Yes, according to wikipedia, HCN has an aroma of "Oil of bitter almond". Also, what temperature environment were you in when this happened. If it was
above 26°C, then all of the HCN would be a gas. If it was below, it would have a very saturated vapor phase. If it was in a lab freezer, not much
would have come off.
When the police come
\( * O * )/ ̿̿ ̿̿ ̿'̿'̵͇̿̿з=༼ ▀̿̿Ĺ̯̿̿▀̿ ̿ ༽
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Boffis
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@NexusDNA
I suggest you simply dissolved the salt in the minium of water at about 70 C, heat to c 90 C, filter hot with a Buchner set-up and cool. If you want
the re-crystallised product in a nice granular powder then stir the cooling solution periodically. If you just leave it to cool you will get nice big
red crystals.
One interesting point about chlorate contamination in ferricyanide is that they react in the presence of a little acid to give "black Prussiate of
Potash", a little insoluble blue precipitate and cyanuric acid if carried out in aqueous solution. The formation of the latter compound is interesting
as I suspect that it probably forms from liberated cyanogen chloride via polymerisation and hydrolysis. I have carried out this reaction in the past
and have a write-up on my computer somewhere.
The significance of this reaction is that a moist mixture might react to generate free cyanogen chloride which has a pungent penetrating smell and is
very lachrymatory even at low concentrations. The addition of a very small amount of alkali to the solution when re-crystallising it will completely
prevent this reaction. Since cyanogen chloride reacts with cyanide (I am not sure about complex cyanides though) to generate dicyanogen NC-CN it may
be this that you can smell, it is poisonous too but not as lachrymatory (causes tiers). Black Prussiate of Potash is I seem to recall potassium
aquopentacyanoferrate(III) and is discussed in one of the books in the forum library -Cyanogen compounds by H E Williams.
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woelen
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Red prussiate of potash (potassium ferricyanide) should be totally odorless. I have this chemical from two different sellers and both samples are fine
red/brown crystals without odor.
I also am surprised to read that the chemical contains 1% of potassium chlorate. Why would one ever want to add that to the chemical? Is this some OTC
product, intended for some particular use, or is it meant to be a general lab reagent? The 1% chlorate totally spoils the material for many
experiments. Chlorate is quite reactive, especially at low pH and would modifiy the outcome of many experiments with this potassium ferricyanide.
Ferrocyanide and ferricyanide are only marginally toxic and they find many applications in hobbies like photography and even food preparation. The
cyanide ion is connected to the iron core very tightly! I added these chemicals to strong acids like 30% H2SO4 and even under such conditions you
hardly get any HCN. You really need to heat the material in combination with strong acids to get HCN. A nice experiment is to make the free acid
H4Fe(CN)6. This demonstrates how well the cyanide ligands are attached to the iron core.
[Edited on 25-11-13 by woelen]
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NexusDNA
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I see! @Boffis thanks for the thorough explanation, I'll try to check the book. Problably adding a weak base will work then!
@woelen, it's intended to be be used as a reagent. I too, was puzzled by the chlorate impurity. I wonder what was the process for producing it, maybe
using chlorine as a catalyst?
By the way, is there a way to remove the chlorate without reacting the other compound?
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Boffis
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By the way, is there a way to remove the chlorate without reacting the other compound?
Yes recrystallize it from water is the best.
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NexusDNA
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Alright I'll try it. Thanks for the help!
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