papaya
National Hazard
Posts: 615
Registered: 4-4-2013
Member Is Offline
Mood: reactive
|
|
Strange KMnO4 reaction ?
Hello folks, just a quick question that puzzles me.
Recently I was doing a sodium zincate(Na2Zn[OH]4) synthesis from ZnO and NaOH pellets (both are of unknown purity, brought from
some lab) and all went well leaving completely clear water solution on heating. I added NaOH gradually to ZnO/water suspension on heating and stirring
after everything dissolves to prevent too much hydroxide usage. After I got a clear solution I added a single crystal of KMnO4 to this
about 30ml of solution, it sunk and started to dissolve leaving pink colored tails if you are familiar. Don't ask me why I needed some manganese there
- I'm trying to make ZnS/Mn phosphore, that's an other story.
Now what went WRONG is this: instead of getting pink solution I got a bluish-grey one - perhaps something is reducing permanganate to manganate ? But
isn't manganate green ? It was reacting quickly because pink tails which permanganate leaves were fading quickly on stirring. In the end I got 30ml of
solution almost blue and this just from a single of KMnO4 !
As far as I know zinc normally doesn't have oxidation states higher than +2, which is already the zincate! Now, what is the reducing agent then ? Also
what blue color manganese compound/oxidation state is possible ?
Thanks, you can try to replicate, interesting to know.
|
|
|
Ozone
International Hazard
Posts: 1269
Registered: 28-7-2005
Location: Good Olde USA
Member Is Offline
Mood: Integrated
|
|
Mn(V) is blue.
O3
-Anyone who never made a mistake never tried anything new.
--Albert Einstein
|
|
|
papaya
National Hazard
Posts: 615
Registered: 4-4-2013
Member Is Offline
Mood: reactive
|
|
Hm, interesting, but how ?
|
|
|
ave369
Eastern European Lady of Mad Science
Posts: 596
Registered: 8-7-2015
Location: No Location
Member Is Offline
Mood: No Mood
|
|
Sodium zincate, as a salt of a strong base and a very weak acid, is strongly basic. Strongly basic conditions stabilize the manganate and
hypomanganate ions (VI and V respectively), and permanganate gets reduced to manganate and hypomanganate. Usually you get manganate, but sometimes, in
very basic solutions, hypomanganate is achievable as well.
OH- is usually the reducing agent, it is oxidized to O<sub>2</sub>. But if ZnO is of unknown purity as you say, any goddamn thing can be
in there and act as a reducer.
Smells like ammonia....
|
|
|
papaya
National Hazard
Posts: 615
Registered: 4-4-2013
Member Is Offline
Mood: reactive
|
|
Thanks for the response, I hoped that "goddamn" thing you mentioned might be quite known among this audience 
What I mean is the most "popular" friend of zinc - cadmium ? arsenic ?? What if water gets oxidized to oxygen, while zincate is a catalyst ? If
someone could replicate...
|
|
|
ave369
Eastern European Lady of Mad Science
Posts: 596
Registered: 8-7-2015
Location: No Location
Member Is Offline
Mood: No Mood
|
|
Is this ZnO some form of consumer product? If so, it couldn't be arsenic or cadmium, this kind of toxic crap is almost never released to the public.
Smells like ammonia....
|
|
|
woelen
Super Administrator
Posts: 8014
Registered: 20-8-2005
Location: Netherlands
Member Is Offline
Mood: interested
|
|
At very high pH, permanganate does not need any reductor to be converted to manganate. Just as a test, take some NaOH and dissolve in water, make a
fairly concentrated solution. Add a single crystal of KMnO4. Your solution will turn green/blue. This green/blue color is the color of manganate(VI).
I doubt you get manganate(V). That stuff is purely blue, having no green hue. It is very unstable and quickly decomposes to manganase(IV). Have a look
at this web page:
http://woelen.homescience.net/science/chem/solutions/mn.html
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
