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Author Topic: NO2 produced during synthesis of Nitric acid.  (Read 4422 times)

Offline SorryDnoodle

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NO2 produced during synthesis of Nitric acid.
« on: 11/11/2014 12:52:16 »
Hi, I am going to be synthesizing and then writing a report about nitric acid, comparing making it by stuff you can buy in a store and a labb and I cannot find a good answer for why NO2 is produced.

I am using a nitrate salt (KNO3) mixed with H2SO4 and then distilling of the HNO3
H2SO4 + 2 KNO3 => K2SO4 + 2 HNO3
This is the simple equation.
I know that HNO3 can react with H2SO4 to make NO2+ but does this go out of solution and out as a gas?

I am a bit bewildered about all this so your help would be appreciated.
Thank you.


 

Online chiralSPO

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Re: NO2 produced during synthesis of Nitric acid.
« Reply #1 on: 11/11/2014 13:27:51 »
Concentrated nitric acid can react with trace impurities to produce NO2 (even just a bit of dust that got into your glassware, or a residue of organic matter that was dissolved in whatever you used to wash your glassware.) I don't know what type of glass you are using, but it may contain trace amounts of oxidizeable metals (Fe2+ or Cr3+). Most concentrated nitric acid contains some dissolved NO2 or N2O4 (that's why it is yellow/orange/red.)

How much NO2 are you observing? Also, what concentration of sulfuric acid are you using? Is it colorless or yellow/brown?
« Last Edit: 11/11/2014 16:03:52 by chiralSPO »
 

Offline SorryDnoodle

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Re: NO2 produced during synthesis of Nitric acid.
« Reply #2 on: 12/11/2014 22:26:24 »
I have not done the "Homemade" version of this experiment yet, the point of the experiment is to observe the difference from the end product (Nitric acid) by using lab grade products and on the other hand using things I can gather for myself ( Store, online etc..)

I used lab grade 18 molar sulfuric acid - and is colorless - and lab grade Potassium nitrate, the glassware is most likely the source of the contamination, the lab I am working in is good, but it lacks a good cleaning setup, simple water and dish soap.

But I am wondering: May small amounts of the HNO3 breakdown to also release NO2? I was discussing it with my teacher and we both thought that it may be possible, and while looking for an answer online after making this post I found that a person on youtube called Nurdrage had done the exact same thing and attributed the NO2 due to the breakdown of HNO3

The amount of NO2 procured is no large amount, but it is very noticeable with it's color.

Thank you for the reply ChiralSPO!
 

Online chiralSPO

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Re: NO2 produced during synthesis of Nitric acid.
« Reply #3 on: 13/11/2014 01:04:54 »
I suppose it could be possible for the HNO3 to "break down" to NO2, but that's formally a reduction, which means something must be getting oxidized in the process. I have never heard of nitric acid disproportionating (reducing/oxidizing itself), but I suppose that at a high enough temperature there could just be a homolytic fragmentation of the form HNO3 --> HO• + •NO2. That said, HO• is extremely reactive, and would oxidize almost anything it came into contact with, so that formalism just kicks the can down the road...

For most applications NO2 contamination shouldn't matter, but if it were a real problem, you should be able to remove the impurity by bubbling nitrogen gas through the produced nitric acid (with a glass bubbler--NEVER put plastic in contact with nitric acid unless you have verified that it is a compatible type, and most plastics are not!)
 

Offline SorryDnoodle

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Re: NO2 produced during synthesis of Nitric acid.
« Reply #4 on: 13/11/2014 16:13:42 »
Thanks, I may try that N2 bubbling thing!

Any suggestions of producing the gas chemically?
 

Online chiralSPO

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Re: NO2 produced during synthesis of Nitric acid.
« Reply #5 on: 13/11/2014 19:26:17 »
producing which gas?
 

Offline Bored chemist

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Re: NO2 produced during synthesis of Nitric acid.
« Reply #6 on: 13/11/2014 21:35:07 »
Decomposition of nitric acid to give NO2 is perfectly plausible, especially in the presence of H2SO4 to act as a dehydrating agent.
2 HNO3 --> H2O + N2O5
2  N2O5 --> 4 NO2 + O2
 

Offline SorryDnoodle

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Re: NO2 produced during synthesis of Nitric acid.
« Reply #7 on: 15/11/2014 22:14:26 »
producing which gas?

Nitrogen to bubble out the NO2
(N2)
Decomposition of nitric acid to give NO2 is perfectly plausible, especially in the presence of H2SO4 to act as a dehydrating agent.
2 HNO3 --> H2O + N2O5
2  N2O5 --> 4 NO2 + O2


Thank you sir, helps a lot!
 

Online chiralSPO

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Re: NO2 produced during synthesis of Nitric acid.
« Reply #8 on: 18/11/2014 19:42:31 »
producing which gas?

Nitrogen to bubble out the NO2
(N2)


hmm... I wouldn't recommend many reactions for producing nitrogen gas, I was assuming that in a lab setting you might have access to compressed or liquid nitrogen, which could easily be bubbled through the nitric acid in a controlled fashion (you really don't want to splash concentrated nitric acid around). It's possible CO2 could be used instead, if that is easier.

Honestly, unless you're trying to do some spectroscopy or mechanistic work or something sensitive like that, I would just use the nitric acid as it is. Almost every bottle of concentrated nitric acid I have used has a slight yellow tint to it from the NO2, and the stuff without is much more expensive.
 

Offline SorryDnoodle

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Re: NO2 produced during synthesis of Nitric acid.
« Reply #9 on: 21/11/2014 21:44:19 »
Quote
I was assuming that in a lab setting you might have access to compressed or liquid nitrogen

Unfortunately no, the lab I am in have nothing like this, it is fairly basic.
I suppose I will just leave as is.

Thanks for all the replies and help!
 

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Re: NO2 produced during synthesis of Nitric acid.
« Reply #9 on: 21/11/2014 21:44:19 »

 

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