SimplyChem16
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Mysterious Brown Gas. Not Bromine.
I had recently performed the "smoke bomb" reaction between Potassium Nitrate, and sugar. After the reaction had completed, a thick paste of
yellowish/white material covered the reaction vessel. I had read this was Potassium Carbonate, so I decided to try to neutralize it simply using
Hydrochloric Acid. Well, much to my surprise, lots of brown looking gas was evolved, and frankly, moved my butt away from that thing as quickly as I
could. Could anybody out there provide an explanation to what happened? 
(Nitrogen Dioxide Perhaps?)
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gdflp
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It is unlikely that much K2CO3 was formed. Mostly it would be potassium nitrite (KNO2) depending on the ratio of sugar to nitrate. When this reacts
with an acid nitrous acid (HNO2) is formed which is unstable and decomposes to water and nitrogen oxides. The brown gas is most likely nitrogen
dioxide.
[Edited on 21-7-2014 by gdflp]
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Zyklon-A
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Yep, your right.
Nitrogen dioxide (or more correctly speaking, dinitrogen tetroxide) is evolved when a nitrite (in this case KNO2) reacts with an acid:
2 KNO2 + 2 HCl (aq) → 2 KCl + 2 HNO2 ↔ 2 HNO2 → NO2 + NO +
H2O
[EDIT] Looks like gdflp beat me to it, anyway.
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I had read this was Potassium Carbonate, so I decided to try to neutralize it simply using Hydrochloric Acid.
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There probably is some K2CO3, but if the KNO3 was in excess, then it would have been partially reduced to
KNO2:
2 KNO3 + H2CO (relative empirical formula for sucrose) → CO2 + H2O + 2
KNO2
Vs. the correct stoichiometry of the oxidation reaction:
2 KNO3 + 2 H2CO (relative empirical formula for sucrose) → 2 CO2 + 2
H2O + K2O
And finally, the CO2 reacts partially with the K2O to produce K2CO3:
CO2 + K2O ↔ K2CO3 . At STP, the reaction goes to completion, but
at the high temperatures of the reaction, it's at equilibrium.
[Edited on 21-7-2014 by Zyklon-A]
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SimplyChem16
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Here's a video, since I have the opportunity to provide you with one
http://tinypic.com/r/55p9js/8
Thanks for the replys!
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Brain&Force
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Most certainly NO2. However, it is a mixture of colorless dinitrogen tetroxide and nitrogen dioxide, which imparts the brownish color.
At the end of the day, simulating atoms doesn't beat working with the real things...
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Zyklon-A
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Are you sure N2O4 is colorless?
Per Absorption of Nitrous Gases:
Which states that at 30°, only ~ 12% N2O4 dissociates into NO2. So, perhaps N2O4 exhibits
color as well?
I guess you're probably right, ~12% is likely enough to produce the color, we see at STP.
[Edited on 21-7-2014 by Zyklon-A]
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Amos
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In any case, SimplyChem, if the smell of nitrogen dioxide isn't enough to keep you away, remember that it is acutely toxic, in case you didn't already
know. Nasty stuff.
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SimplyChem16
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To be honest, I hadn't smelled the "characteristic sharp, biting odor" that comes with the gas. There was a fair amount of wind though
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papaya
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If you could improve the reaction in a way that the end products contain mostly KNO2, then you have a simple way to get nitrites (unless you can buy
them).
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Fantasma4500
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interesting.. nitrites from KNO3 is said to be relatively hard
NaNO3 is preferred at least for charcoal and molten NaNO3
surprisingly pure product if you let all the impurities settle
also NO2 doesnt have a sharp biting odor if you ask me, i'd say its more roundish and thick / choking, ofcourse more choking the more there is in the
air of it
SO2 has a sharp biting odor however -- if you ask me, supposing not 100% of all chemists would agree
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