Sciencemadness Discussion Board

Nitric acid via nitrate salt & NaHCO3 or H2CO3

White Yeti - 26-8-2011 at 08:35

Hello everyone.

Pure nitric acid is synthesized when sulfuric acid reacts with a nitrate salt. Trading one acid for another seems ridiculous, so another method involves the use of sodium bisulphate instead of sulfuric acid.

I had an idea that goes even further, in HSO4-, the only atom you're really interested in, is the hydrogen atom because it combines with the nitrate ions to form nitric acid that boils off.

So in theory you could use a bicarbonate salt to generate nitric acid...

NaHCO3+ NaNO3<--->Na2CO3+ HNO3

This is an equilibrium, but if the nitric acid boils off, the reaction continues (slowly) until the reagents are used up.

There's one problem though, bicarbonate decomposes at medium temperatures, so I cannot perform a dry distillation.
If I mix the two chemicals together in water and then heat to 100C+, would I get a distillate of dilute nitric acid?

One more question, can carbonic acid be used instead of a bicarbonate salt? The dissociation constant for carbonic acid is much higher than for bicarbonate. I would have to use a pressure vessel to contain the carbon dioxide and use some kind of "cold finger" to condense water and (hopefully) nitric acid.

I'm aware that pure nitric acid cannot be obtained via these methods (if any at all), but I'm not interested in getting the pure stuff because I will need to dilute it down again for most of my purposes.

Thanks for reading.

not_important - 26-8-2011 at 08:42

The CO2 is more volatile than HNO3, so it will gas off even at low temperatures never mind the Ka values of the propossed reactants. The Ka differences set the equilibrium far to the side of the nitrate salt, so the answer to your question is - basically no.

Very high pressures of CO2 plus concentrated nitrate (Na or K NO3) solutions can do sort of what you want to, but you have to filter off the precipitated bicarbonate under pressure. After that the remaining NaHCO3 in solution will react with some of the HNO3 once the pressure is removed, after which you could concentrate, filter off NaNO3, then distill HNO3 off. Remember the H2O+HNO3 form a high boiling azeotrope, water will distill from dilute HNO3 until the concentration approaches the azeotrope.



White Yeti - 26-8-2011 at 09:01

I knew there was a catch somewhere :\
Filtering off the bicarbonate under pressure sounds like mission impossible. How much pressure do you think is needed to drive the reaction forward? Do I need to cool the mixture? It seems like a failed venture, but I would like to know as much as possible before I drop the idea.
Thanks.

[Edited on 8-26-2011 by White Yeti]

Otter - 26-8-2011 at 15:58

One other method you could use is react aluminum metal with a stoichiometric amount of concentrated HCl if you do have access to it. HCl is easily found at masonry supply stores, I got a gallon of 31.4% HCl for $10. The reaction will of course generate:

Al + 3HCl + 6H2O -> 3Cl- + Al(H2O)6 3+ + 3/2 H2 gas.

Here's the trick:

Since Al3+ has an incredibly high positive charge density for a very tiny ion, it is a VERY strong Lewis acid. This ion will complex with water to form Al(H2O)6 3+.

Because the Al3+ is so tightly bound to the O atoms in water, this will make the water complexed to it VERY acidic. In fact solutions of AlCl3 in water can reach pH values between 0 and 1, it's that strong an acid.

See: http://en.wikipedia.org/wiki/Aluminum_chloride#Reactions_wit...

Once you have a solution of hydrated aluminum and chloride ions, boil it down until it stops spewing HCl gas or at least slows down, THEN you add sodium nitrate:

You will be almost guaranteed that because NaCl is much more stable than HNO3, HNO3 will boil out of the solution, along with a little bit of HCl contamination.

It's worth a shot. :)

unionised - 27-8-2011 at 04:41

It's worth a shot if you want NOCl, Cl2 etc.

Otter - 27-8-2011 at 05:24

Quote: Originally posted by unionised  
It's worth a shot if you want NOCl, Cl2 etc.


You've tried this? :D

[Edited on 27-8-2011 by Otter]

not_important - 27-8-2011 at 07:36

Quote: Originally posted by Otter  
...
Once you have a solution of hydrated aluminum and chloride ions, boil it down until it stops spewing HCl gas or at least slows down, THEN you add sodium nitrate:

You will be almost guaranteed that because NaCl is much more stable than HNO3, HNO3 will boil out of the solution, along with a little bit of HCl contamination.

It's worth a shot. :)



constant-boiling azeotrope at 68% HNO3 boils at 121 °C
constant-boiling azeotrope at 20.2% HCl and 108.6 °C

which will distill off first?

Also:

http://www.sciencemadness.org/talk/viewthread.php?tid=12612

Note that NaCl has a lower solubility than NaNO3 in hot water, so it may ppt out of the solution and then could be removed. But you'll still have ~360 g/L of NaCl in solution.

This all ignores that AlCl3 in water can give chlorohydrates, and that removing HCl from such a solution will leed to the formation of hydrated Al(OH)3 and more chlorohydrates.


Otter - 29-8-2011 at 14:03

Okay, second attempt. :D

Instead of using NaHCO3, use NaHSO4, or sodium bisulfate. It's easily bought as a pH reducer for pools. HSO4- is a strong acid.

Just put together NaHSO4 and NaNO3 in water, and boil it, and condense the vapors. Since nitric acid is on the borderline between "strong" and "weak", the following should happen:

HSO4- + NO3- -> HNO3 + SO4 2-.

You'll get a block of sodium sulfate left, the nitrate having converted to nitric acid. This'll *probably* go better than my original suggestion. :D

White Yeti - 2-9-2011 at 15:11

Your first idea seemed very plausible, but it makes more sense to use aluminium in slight excess. That way, you would be sure that there is no extra HCl left. Since nitric acid doesn't attack aluminium, you could even have it in large excess.

But there is a gaping hole in your theory. Nitric acid will react with aluminium chloride to yield aluminium nitrate and nitrosyl chloride. The Raging Nurd has a video on how to make aluminium nitrate and he mentions that very reaction.

Would acetic acid work for making nitric acid? If you think about it, reacting aceitic acid with calcium nitrate would yield nitric acid and calcium acetate that precipitates out. Filtering out the calcium acetate and boiling off the nitric acid continually would drive the equilibrium to completion.
Any thoughts?

Random - 2-9-2011 at 21:57

Quote: Originally posted by White Yeti  
Your first idea seemed very plausible, but it makes more sense to use aluminium in slight excess. That way, you would be sure that there is no extra HCl left. Since nitric acid doesn't attack aluminium, you could even have it in large excess.

But there is a gaping hole in your theory. Nitric acid will react with aluminium chloride to yield aluminium nitrate and nitrosyl chloride. The Raging Nurd has a video on how to make aluminium nitrate and he mentions that very reaction.

Would acetic acid work for making nitric acid? If you think about it, reacting aceitic acid with calcium nitrate would yield nitric acid and calcium acetate that precipitates out. Filtering out the calcium acetate and boiling off the nitric acid continually would drive the equilibrium to completion.
Any thoughts?


CO2 doesn't react with Ca(NO3)2 because it isn't stronger acid than nitric, so it wont work. Neither should acetic acid work because calcium acetate is soluble as I saw.