Foeskes
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Mysterious compound
Last week, I went to my local school supply store (they sell lots of chemicals there) and bought ammonium dichromate, the bottle looks like it has
been there for many years. After I got home and opened it, I found out that it isn't ammonium dichromate but a clear solid crystal that looks like
sodium thio sulfate when I poured it out a bit of liquid came too, so it's probably hygroscopic. It's a somewhat strong reducing agent reacting with
permanganate to form manganese dioxide and reducing hypochlorite with a exothermic reaction. However unlike thiosulfate it reacts with dilute sulfuric
acid to form a deep red compound (kinda like permanganate mixed with MnO2) with no gas produced it doesn't seem to be exothermic either.
What might this possibly be?
EDIT: it's likely thiocyanate, it reacts with iron(III) sulfate forming a blood red solution. Its dissolution is endothermic.
[Edited on 9-9-2017 by Foeskes]
[Edited on 9-9-2017 by Foeskes]
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ave369
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Is thiocyanic acid deep red? Or is it just iron contamination in sulfuric acid?
Smells like ammonia....
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Foeskes
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I'm starting to think its not it, since cobalt(II) is SUPPOST to make a blue compound but I got a deep red compound. The red also seems to have low
solubility in water.
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nezza
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It sounds like potassium thiocyanate. It is quite hygroscopic and old bottles will have liquid in them unless extremely well sealed.
If you're not part of the solution, you're part of the precipitate.
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j_sum1
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I would have thought ammonium thiosulfate was more likely -- at least a more likely mislabel.
You could test with NaOH to see if it is an ammonium salt. Maybe do a flame test if that comes up negative.
[Edited on 9-9-2017 by j_sum1]
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Foeskes
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Ok, I reacted it with NaOH. The reaction definitely produced ammonia.
Any more test for thiocyanate?
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j_sum1
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Well the rust-blood complex with Fe3+ is as far as I know unique. Nothing else reacts with ferric in that way.
Is it possible that your Co is impure and the normal colour is masked?
Edit
I note that Co(SCN)2 is a bright red colour. A (very) quick search gave me nothing on the complex. I think this means the puzzle is solved.
[Edited on 9-9-2017 by j_sum1]
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nezza
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Mix some of the solution 50:50 with acetone. Adding cobalt(II) to this solution should give a bright blue complex. Be aware that any iron(III)
contamination may mask the colour. Iron(III) can be removed by the addition of fluoride. Here is a picture of the cobalt(II) thiocyanate complex in
50% acetone.
[Edited on 14-9-2017 by nezza]
If you're not part of the solution, you're part of the precipitate.
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woelen
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If you have access to nitrite, then you can check for thiocyanate as follows:
Dissolve some of the mystery solid in 10% H2SO4 (not HCl)
If it is a thiocyanate, then the solution remains colorless if the H2SO4 does not contain any iron(III).
Add a little amount of solid NaNO2 or a ml or so of highly concentrated NaNO2-solution.
If you have thiocyanate, then a deep red solution is obtained, which slowly decomposes, giving bubbles of gas and a white fume.
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