Sciencemadness Discussion Board

Dry Nitric acid

v4nt3d - 24-1-2016 at 02:54

Hello everyone! I'm kinda new to practical chemistry and I'd like to ask you a question - is it possible to dry nitric acid? From my knowledge, I know that there're a few drying agents, such as anhydrous sulfates, sodium chloride, molecular sieves, silica gel, etc. I made my nitric acid using the Cu/HCl/KNO3 method producing NO2 and then bubbling it into 30% H2O2.
In my opinion, NaCl and sulfates won't work, because they'll dissolve in the weak nitric acid and water. I also don't have molecular sieves, so I'm left with only 1 choice - silica gel. So, is it possible to add powdered silica gel to the nitric acid, wait some time and finally get an azeotropic nitric acid?

Bot0nist - 24-1-2016 at 06:21

Distill with concentrated sulfuric acid and you'll obtain red fuming nitric acid > 95%.

hissingnoise - 24-1-2016 at 06:55

Here's one of several threads on the subject.

http://www.sciencemadness.org/talk/viewthread.php?tid=26106

v4nt3d - 24-1-2016 at 07:49

I don't have access to sulfuric acid nor to glassware.

hissingnoise - 24-1-2016 at 08:15

You'll soon, I'm sure, remedy that situation, once you develop enough interest in chemistry!

Amos - 24-1-2016 at 08:24

Wikipedia states that anhydrous magnesium nirate, which forms di- and hexahydrates, can be used to dry azeotropic nitric acid, but I don't have any reference as to how dry one can make nitric acid using it.

Tsjerk - 24-1-2016 at 10:12

The problem is that you need anhydrous nitric acid to make anhydrous magnesium nitrate.

If you by chance would have anhydrous magnesium nitrate you can calculate how much you would need by assuming it would go the lowest hydrate.

BromicAcid - 24-1-2016 at 10:44

You may be able to use sieves to accomplish something. Most standard drying salts, i.e., magnesium sulfate, are going to simply dissolve due to all the water around. It's not the same as trying to eek the last few % of water out of an organic solvent.

chornedsnorkack - 24-1-2016 at 13:38

Quote: Originally posted by Bot0nist  
Distill with concentrated sulfuric acid and you'll obtain red fuming nitric acid > 95%.


Red. What´s the remaining 5 %? H2O? N2O4? N2O5?

You cannot get a *dry* HNO3 by *drying* - the same is true of H2SO4. There is no way to hit exactly "100 %", because there is a reversible equilibrium:
2HNO3<->H2O+N2O5
Use a good drying agent, like P4O10, and what you get is N2O5, not "dry HNO3".

The logical way to get 100 % HNO3 is by solidification. Crystal growth rejects impurities. The melting point of HNO3 is -41 degrees. Of the eutectics, the first eutectic of HNO3/H2O is at 91 % HNO3 by weight, and melts at -60 degrees. So, if you have fuming nitric acid of 95 %, you could freeze about half of it on cooling from -50 to -60 degree, and reject your water by draining (and then wiping?) -60 degree 91 % nitric acid off your pure nitric acid crystals.
What happens to the eutectic mixtures when the impurity is N2O4? N2O5? H3PO4?

Tsjerk - 24-1-2016 at 14:45

And what would be the difference between the HNO3/N2O5/H2O mixture gained after drying with for example P4O10, and the 100% HNO3 gained with your freezing method?

If you would get to 100% with either of them, they will be exactly the same.

chornedsnorkack - 26-1-2016 at 12:23

Quote: Originally posted by Tsjerk  
And what would be the difference between the HNO3/N2O5/H2O mixture gained after drying with for example P4O10, and the 100% HNO3 gained with your freezing method?

If you would get to 100% with either of them, they will be exactly the same.


No.
First, P4O10 will only get precisely equal amounts of H2O and N2O5 if you happen to use the correct amount of desiccant.
Second, it does nothing to stop irreversible decay to N2O4 and O2
Third, the resulting H3PO4 itself has some solubility.
So: first dry the nitric acid with P4O10 to somewhere near target, like 99 %.
And in the second step, freeze pure HNO3 and remove the last % of water, or N2O5, along with N2O4 and H3PO4 impurities, in the mother liquor.

aga - 26-1-2016 at 12:59

Quote: Originally posted by v4nt3d  
Hello everyone! I'm kinda new to practical chemistry and I'd like to ask you a question - is it possible to dry nitric acid?

Yes.
Quote: Originally posted by v4nt3d  
I don't have access to sulfuric acid nor to glassware.

Then you cannot :-

a) Dry Nitric Acid
b) Use dry Nitric acid.

Do some other amateur chemistry that requires no Glass first.

If you list the reagents available to you then people here can give Useful suggestions about what is possible in your circumstances.

AJKOER - 26-1-2016 at 14:27

My look at the chemistry suggests adding NO2 as was noted in a prior thread on this topic referenced above. To quote:
Quote: Originally posted by AndersHoveland  
If one has 90% conc. nitric acid, and wants to concentrate it further, it can first be saturated with nitrogen dioxide and then a dry stream of ozone passed through. This can bring the concentration up to anhydrous, or even further. This route is most practical for already high concentrations, where one only needs to raise the concentration by a little more.


In place of O3, which may not be available, I would try O2.

[Edit] My take on how the action of ozone on HNO3 saturated with NO2 is proceeding based on some radical reactions. Source: "Simultaneous Multi-Pollutants Removal in Flue Gas by Ozone", pages 50 to 51, by Zhihua Wang, at https://books.google.com/books?id=qKoxBQAAQBAJ&pg=PA51&a... :

R9 O3 + .NO2 = O2 + .NO3

Then:

R115 .NO2 + .NO3 = N2O5

N2O5 + H2O = 2 HNO3

where the final reaction removes water and concentrates the Nitric acid.

[Edited on 27-1-2016 by AJKOER]

chornedsnorkack - 28-1-2016 at 12:04

Quote: Originally posted by AJKOER  
My look at the chemistry suggests adding NO2 as was noted in a prior thread on this topic referenced above. To quote:

Quote: Originally posted by AndersHoveland  
If one has 90% conc. nitric acid, and wants to concentrate it further, it can first be saturated with nitrogen dioxide and then a dry stream of ozone passed through. This can bring the concentration up to anhydrous, or even further. This route is most practical for already high concentrations, where one only needs to raise the concentration by a little more.


In place of O3, which may not be available, I would try O2.

The matter is that the reaction
4NO2+O2+2H2O<->4HNO3 is an equilibrium one. With equilibrium at a rather lower concentration than 100 %. What you need is to force the reaction to the right, away from equilibrium.

chemrox - 28-1-2016 at 17:32

why would anyone without glassware want red fuming nitiric? Are you going to use a metal bowl to trinitrate glycerol? Oh and by the way you need H2SO4 for that one as well.

Marvin - 29-1-2016 at 08:24

This thread seems to have fallen apart somewhat with people taking things other people have said and throwing them in the OPs face. What he was asking to make was azeotropic nitric.

When I was a teenager, nitric acid and nitric oxides seemed easy things to play with because they were accessible. So did acrolein. I was mostly working from old textbooks from the 40's that didn't talk much about safety. I started to question my experiments about the time I got chemically induced pneumonia.

Be wary of short sighted experiments. Chemistry will bite you.

NO2 is insidiously toxic. It damages you without telling you.

Fluorite - 4-2-2021 at 13:32

Sodium pyrosulfate? Can I use it to dry nitric acid?

zed - 12-3-2021 at 19:56

What grade of Nitric Acid do you need? What purpose must it be able to accomplish?

itsallgoodjames - 15-3-2021 at 07:45

Quote: Originally posted by v4nt3d  
I don't have access to sulfuric acid nor to glassware.


Then you shouldn't be working with 90%+ nitric acid

Hey Buddy - 16-3-2021 at 13:54

This technically is "dry"

Attachment: Melamine h2so4 mel hno3.PDF (2.1MB)
This file has been downloaded 371 times

zed - 21-3-2021 at 17:54

Boy, I don't like the looks of that Nitrated molecule.

It looks suspiciously like it might oxidize you off of the face of the planet.