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LearnedAmateur
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When I get around to ordering some more, I’ll try and grow a crystal out of it to see if there’s much colour through a repeating lattice.
Shouldn’t be difficult considering it’s barely hygroscopic, definitely won’t form a solution when left to air (we all know how bad LDPE bags are
for keeping moisture out).
I guess it’s like with colourless solids, they’re clear when crystalline and white when powdered, lots of interfaces for light to reflect off, so
weak colours are likely intensified in the latter case. Can’t find any images of a macroscopic NaNO2 crystal so it’s up for experimentation.
In chemistry, sometimes the solution is the problem.
It’s been a while, but I’m not dead! Updated 7/1/2020. Shout out to Aga, we got along well.
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aga
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Sounds like a Challenge !
Reminds me: made some potassium rhodizonate some time ago, so best stick it in some vinegar and see how contaminated my NaNO2 is, thence to
photos in solution and crystals.
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Magpie
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I made KNO2 by reducing the nitrate with lead. I also bought some lab grade from Post Apple Scientific. Both hav a slight yellow cast.
The single most important condition for a successful synthesis is good mixing - Nicodem
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TheMrbunGee
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My NaNO2 is slightly yellow, but not even close to that yellow as OP KNO2, those are impurities. May be N oxides or some kind of tars from charcoal.
When I played with self made low quality black powder - yellow/brown residue was always left after burning it. It might be because of S, but charcoal
might also be blamed.
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woelen
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I have NaNO2 from two sources. One of them is reagent grade. Both are pale yellow, it is a true yellow color and not brownish.
I also have KNO2. This also is yellow, but this has a faint brownish cast.
Color (like whiteness) does not tell everything. Your NaNO2 or KNO2 can be very impure, e.g. it can contain a lot of NaNO3 or KNO3.
With NaNO2 it is important to assess its purity. You can do that by titration with KMnO4. KMnO4 is quickly reduced to Mn(2+) by nitrite ion at low pH.
Best way to do this is make a dilute solution of KMnO4 in very cold dilute H2SO4 (e.g. 2% H2SO4) of known concentration of KMnO4. Dissolve a well
measured weight of your nitrite in a well measured volume of water and drip this in the solution of KMnO4 while stirring strongly. Continue until the
color of the MnO4(-) ion just disappears.
Do not work the other way around. If you add your acidic KMnO4-solution to the solution of NaNO2 or KNO2 then you'll lose bubbles of NOx and this will
make your titration very inaccurate.
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RawWork
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Add sodium hydroxide until color dissappears, this means contaminant is some nonmetal like N (it's compounds). If it doesn't, then contaminant is some
metal (transition or rare earth, their compounds).
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hissingnoise
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Indeed, since both alkali nitrites are hygroscopic there may be some hydrolysis releasing traces of NO2.
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LearnedAmateur
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I don’t think NaNO2 hydrolyses, not from what I’ve heard. The mechanism behind its ‘conversion’ is through HNO2, nitrous acid, which is weak
enough to be liberated by just about any household acid. It’s quite unstable above 0-5C, decomposing via 2 HNO2 -> H2O + NO2 + NO, at least
that’s what makes sense to me. In fact, it would technically be a dehydration reaction, wouldn’t it?
Edit: actually I’d say you’re partly right there, since you’ve got some NO2 and SO3 floating around in the atmosphere from pollution, they
could make their way into the nitrite, forming acidic vapours with atmospheric moisture.
[Edited on 20-3-2018 by LearnedAmateur]
In chemistry, sometimes the solution is the problem.
It’s been a while, but I’m not dead! Updated 7/1/2020. Shout out to Aga, we got along well.
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