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Author: Subject: Nitric acid color
barley81
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[*] posted on 18-6-2011 at 11:33
Nitric acid color


I poured about 300mL of colorless 70% ACS nitric acid into a glass bottle w/glass stopper lubricated with a small amount of vaseline. The bottle was clean and dried (rinsed with acetone to speed it up), but a very small amount of white film was on the bottom. Then, I wrapped it in translucent foam, put it in an HDPE plastic bottle with the top cut off (just fit, no extra room) and packed the top with paper toweling. Then I stretched a few layers of paper over the top and taped it shut. The acid was left on my workbench inside, below a small window, for about a week and a half. After, it was taken out and had turned yellow(with a green tinge due to the glass). Is the color because of NO2 from sunlight, trace amounts of oxidized vaseline, or the whatever was in the white film? I'm thinking the acid oxidized a tiny amount of vaseline and was reduced to NO2. Should I degrease the stopper and store in a dark place?
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[*] posted on 21-6-2011 at 09:25


NO2 is a reddish/brown colour. More likely your Nitric acid reacted with something.
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[*] posted on 21-6-2011 at 11:29


It will appear yellow in low concentrations. My nitric acid is stored in a very dark location and over time it has gone from clear to slightly yellow, to a bit orange with a haze above it. While a reaction with vasoline is also likely (nitric acid fumes travel in their containers) this color is normal for nitric acid. Keeping it out of the light will slow how long it takes.



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The WiZard is In
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[*] posted on 21-6-2011 at 12:08


Quote: Originally posted by barley81  
I poured about 300mL of colorless 70% ACS nitric acid into a glass bottle w/glass stopper lubricated with a small amount of vaseline.


Well.... my Conc HNO3 which has been stored out-of-doors
year round for 15+ years — when left in the sun for a hour or
so turns light oxide of nitrogen brown. I still wouldn't drink
bath in it other then that it seems to be chemical usable.


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Fleaker
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[*] posted on 21-6-2011 at 21:05


Once I added RFNA to 70% nitric acid and was left with a brilliant green-blue solution. I wonder if the concentrated acid some how oxidized the weaker acid? Anyone else notice this phenomena?



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[*] posted on 21-6-2011 at 21:18


I also have a clear reagent bottle (I have no amber) with 70% HNO3 that has discoloured over time.My understanding is(I haven't tried it) is aerating the the acid will clear the disolved NOx.



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barley81
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[*] posted on 26-6-2011 at 07:42


I just noticed that the acid has brown NO2 gas above the liquid. I'll let it sit in the dark from now on, maybe it'll clear up. If that doesn't work, I'll try aerating it as suggested. Thank you all for your answers!
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mr.crow
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[*] posted on 26-6-2011 at 08:21


My reagent grade acid is fine sitting in the dark. Comes in a clear bottle.

So I made some RFNA and added it to water to make a 70% solution. Of course it got very hot and decomposed a little. The solution is still piss yellow and has a slight color above the solution.

How do I make the solution clear? Don't think we got a solid answer here.


[Edited on 26-6-2011 by mr.crow]




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[*] posted on 26-6-2011 at 11:36


Quote: Originally posted by mr.crow  


How do I make the solution clear? Don't think we got a solid answer here.


[Edited on 26-6-2011 by mr.crow]

by vacuum distillation
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woelen
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[*] posted on 26-6-2011 at 12:54


Nitric acid discolors anyway, when its concentration is well above 65%. I have a bottle of 70% nitric acid and I store this in the dark. Still, it has a slight yellow color:

http://commons.wikimedia.org/wiki/File:Nitric_acid_70_percen...

[Edited on 26-6-11 by woelen]




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mr.crow
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[*] posted on 26-6-2011 at 15:25


Looks pretty clear to me.

Thanks for all the great pictures on Wikipedia too




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