Sciencemadness Discussion Board
Not logged in [Login ]
Go To Bottom

Printable Version  
Author: Subject: Mysterious compound
Foeskes
Hazard to Others
***




Posts: 156
Registered: 25-2-2017
Member Is Offline

Mood: No Mood

[*] posted on 8-9-2017 at 16:27
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]
View user's profile View All Posts By User
ave369
Eastern European Lady of Mad Science
*****




Posts: 568
Registered: 8-7-2015
Location: Another goddamn town in Russia
Member Is Offline

Mood: No Mood

[*] posted on 9-9-2017 at 00:18


Is thiocyanic acid deep red? Or is it just iron contamination in sulfuric acid?



Smells like ammonia....
View user's profile View All Posts By User
Foeskes
Hazard to Others
***




Posts: 156
Registered: 25-2-2017
Member Is Offline

Mood: No Mood

[*] posted on 9-9-2017 at 01:25


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.
View user's profile View All Posts By User
nezza
National Hazard
****




Posts: 324
Registered: 17-4-2011
Location: UK
Member Is Offline

Mood: phosphorescent

[*] posted on 9-9-2017 at 03:36


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.
View user's profile View All Posts By User
j_sum1
Administrator
********




Posts: 5690
Registered: 4-10-2014
Location: Unmoved
Member Is Online

Mood: juggling juggling juggling

[*] posted on 9-9-2017 at 04:02


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]
View user's profile View All Posts By User
Foeskes
Hazard to Others
***




Posts: 156
Registered: 25-2-2017
Member Is Offline

Mood: No Mood

[*] posted on 9-9-2017 at 04:21


Ok, I reacted it with NaOH. The reaction definitely produced ammonia.
Any more test for thiocyanate?
View user's profile View All Posts By User
j_sum1
Administrator
********




Posts: 5690
Registered: 4-10-2014
Location: Unmoved
Member Is Online

Mood: juggling juggling juggling

[*] posted on 9-9-2017 at 05:10


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]
View user's profile View All Posts By User
nezza
National Hazard
****




Posts: 324
Registered: 17-4-2011
Location: UK
Member Is Offline

Mood: phosphorescent

[*] posted on 13-9-2017 at 23:46


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.



Cobalt Thiocyanate.jpg - 183kB

[Edited on 14-9-2017 by nezza]




If you're not part of the solution, you're part of the precipitate.
View user's profile View All Posts By User
woelen
Super Administrator
*********




Posts: 7744
Registered: 20-8-2005
Location: Netherlands
Member Is Offline

Mood: interested

[*] posted on 14-9-2017 at 10:19


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.




The art of wondering makes life worth living...
Want to wonder? Look at https://woelen.homescience.net
View user's profile Visit user's homepage View All Posts By User

  Go To Top