Sciencemadness Discussion Board

Nitric Acid Synthesis

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chief - 2-5-2010 at 09:43

... nice (!), only the direct heating by the spiral might be a bit harsh ... :o and your beautiful retort might be history after a while ...

A bath of molten tin might be a good heat-transfer-medium for such a purpose: Tin is known to have quite a low vapor-pressure, and is therefore used in industrial manufacture of float-glass, where liquid glass rests on a hot tin-bath ...
==> Only the tin should be clean, no lead or arsenic or antimony in it ... !

Formatik - 2-5-2010 at 09:51

Quote: Originally posted by Mildronate  
Here you can see my retort, its made from 1liter flash and glass pipe. I use it only for nitric acid.

Here you've poured the powder directly down the snout. Why not get a big funnel, then connect a wide tube to the funnel bottom, then stick that into the snout and slowly pour in the powder? Use a metal rod to swirl around and push the powder down if it gets stuck. That will allow the powder to get down further and not contaminate the nitric acid with potassium. The H2SO4 can be added the same way, even easier. You ought to also have a cooling bath for condensing HNO3.

Mildronate - 2-5-2010 at 09:53

Its made from pyrex glass soviet analog. I think about 5liter retort. Of course i had cooler too, but retort to my mind is best for nitric acid.

Mildronate - 2-5-2010 at 09:55

That was first time with my new retort. There was litlle bit of water in it thats way KNO3 is on its neck.

Mildronate - 2-5-2010 at 09:56

Good idea about funnel thanks

hissingnoise - 2-5-2010 at 11:30

Retorts are very inefficient for HNO3 distillation, but if the receiver is cooled by water from a tap spilling onto it the HNO3 vapours will condense reasonably well.
The standard distillation apparatus is far better suited to HNO3 production.

Mildronate - 2-5-2010 at 11:36

to my mind retort is better than destilation setup with cooler, i had both.

hissingnoise - 2-5-2010 at 11:50

Whoops! I've just noticed the encrustation of salt in the spout - to my mind it looks a lot like carelessness.

Mildronate - 2-5-2010 at 11:53

thats true but its because retort was wet from water :(

hissingnoise - 2-5-2010 at 12:09

Does your retort have to be charged through the spout?
If it does, getting reasonably pure HNO3 from it will be very difficult.

Mildronate - 2-5-2010 at 22:13

of course from spout

kilowatt - 2-5-2010 at 23:56


Heating NH4NO3 has to be done very carefully, as the salt is prone to unstable decomposition, esp. if contaminated; thus synthesis via NH4NO3 is not recommended pathway.

Carefully indeed, but if you meet that requirement it's fine. The temperatures involved here are well below the melting/decomposition temperature of ammonium nitrate (210°C or more) as long as you use a uniform heat source and boiling chips. I did this too and it works very nicely giving near perfect yield. I used fertilizer grade ammonium nitrate and drain cleaner grade sulfuric acid in aqueous solution.

The vapor and reflux inside the column was clear, indicating that no ammonia was being given off from the flask, and the gas scrubber on the vent (which doubled as the condenser cooling water) remained at steady pressure when the distillation had stabilized, indicating that no N2O or other gas was being given off.

Doing an anhydrous distillation under vacuum should be a further improvement.

HPIM1670.JPG - 108kB

[Edited on 3-5-2010 by kilowatt]

Contrabasso - 8-5-2010 at 04:43

A distillation retort should have a separate filling point usually with a ground glass stopper, and also usually at the top when in the distillation position.

The obvious production of brown fumes indicates decomposition on a big scale. Distillation of Nitric Acid requires the use of vacuum to get the boiling temperature below the decomposition temp. Also it is necessary to break the azeotrope to get NA greater than 68%.
At the reduced boiling point under reduced pressure perhaps a hot water heating bath will suffice.

Does anyone have some links or references to reasonable temperatures and distillation vacuums to get white nitric acid. I have ground glass distillation apparatus and and aspirator/filter pump. I can pump iced water through the condenser but do I really need better?

Mildronate - 8-5-2010 at 11:35

You no need links for vacum temperatures there is universal tables (monograms, i dont know is it correct in english). Nitric acid can easy purifiy from NO2 with air or carbamide. There is no azetrope when you use sulfuric acid + nitrate method.

drying ammonia

Formatik - 18-5-2010 at 17:56

Quote: Originally posted by Formatik  
... Drying agent and material. In the bottle above, CaCl2 pellets were used. Other drying agents will work, CaO, Na2SO4, MgSO4, etc. In the industry liquid ammonia is used, so no need for drying.

Note again about these drying agents. I didn't notice it much in my experiment, but CaCl2 (many soluble calcium salts, solubility of ammonia is higher in Ca(NO3)2 than pure water) will fixate ammonia. In fact, ammonia has the greatest tendency to form complexates with dissolved calcium ions than other alkaline earths (see: Dawson, McCrae, J. Chem. Soc. 1901, 79 [II], 1069). From those listed above, CaO is the best choice for drying ammonia. It is less harsh than KOH or NaOH, and won't ruin glass either. According to a chart in Gas Mixtures by Gary O. Nelson, average efficiency of MgO is close to as good as CaO. BaO is the strongest dehydrant suitable. With powders though, there is the extra need to filter for the ammonia so no dust comes over into the catalyst.

Chainhit222 - 2-6-2010 at 14:35

So yesterday I made some nitric acid. I used KNO3 and H2SO4 and distilled a clear liquid under aspirator vacuum.
The glass was baked in the oven prior to use, the KNO3 was baked in the oven prior to use, and the H2SO4 drain cleaner was boiled on the BBQ till it was fuming, and it was let to cool off to a use able temperature (unstoppered though).
The density of this nitric acid was 1.497 at standard pressure @ 4 degrees Celsius (did not measure room temperature). I assume this to be around 80-85% HNO3.

It was stored in the fridge overnight (at around 4 degrees c) in a ground glass flask with a ground glass stopper and vacuum grease.

Today I decided to re distill it over sulfuric acid to increase the purity. It came over at about 50c. I mixed equal volumes of my HNO3 and fuming h2so4. This time I left the H2SO4 on the grill while it was fuming, and stoppered it with a ground glass stopper while the flask was still hot (maybe 200c), and let it cool to room temperature prior to adding it to the nitric acid. Again, the glassware was baked in the oven prior to use.

I have measured the density of the nitric acid at about room temperature, and it is only 1.477, meaning the nitric acid is less then 90% after I vacuum distilled it from sulfuric acid. I only distilled half the volume of the nitric acid (started with 100ml hno3 and 100ml h2so4 in the boiling flask, and I stopped distillation at 50ml in the reviving flask.

I was under the impression that this distillation should have left me with like 95%+ HNO3. What the hell is going on?

Someone suggested that water vapor might be getting sucked in through the aspirator, but I find that hard to believe, as other members on this board seem to be getting 95+% hno3 using aspirator vacuum.

The KNO3 I am using is pyro grade.

Am I not heating the H2SO4 enough? I heated it to a point where it was spewing thick, choking, unpleasant fumes.
What is the secret to performing this distillation?
And the scale I am using is a MXX-123, which claims to have a uncertainty of 0.663 milligrams... .
The volume is measured using a 10ml graduated cylinder.
what the fuck this shit??! :mad:

[Edited on 2-6-2010 by Chainhit222]

Lambda-Eyde - 2-6-2010 at 14:40

What is the accuracy of the graduated cylinder? That might be your problem.

Edit: You could perhaps titrate it if you think the cylinder is the source of error?

[Edited on 2-6-2010 by Lambda-Eyde]

Chainhit222 - 2-6-2010 at 14:50

How do I find out the accuracy of my graduated cylinder?

It says it on the cylinder, it is +- 0.1ml

I'm suspecting either my scale or the aspirator leaking water, I might try a drying tube next time, unless someone has better advice. And I do not have the equipment to perform a titration.

[Edited on 2-6-2010 by Chainhit222]

[Edited on 2-6-2010 by Chainhit222]

hissingnoise - 2-6-2010 at 15:01

Am I not heating the H2SO4 enough? I heated it to a point where it was spewing thick, choking, unpleasant fumes.

When boiling down dilute H2SO4, a choking steam appears long before the last of the water boils off.
You should continue the boiling until the appearance of the fumes changes from a heavy steam to a much thicker, solid looking white vapour (SO3).
This occurs when the temperature goes over 300*C. . .

Chainhit222 - 2-6-2010 at 15:05

Quote: Originally posted by hissingnoise  
Am I not heating the H2SO4 enough? I heated it to a point where it was spewing thick, choking, unpleasant fumes.

When boiling down dilute H2SO4, a choking steam appears long before the last of the water boils off.
You should continue the boiling until the appearance of the fumes changes from a heavy steam to a much thicker, solid looking white vapour (SO3).
This occurs when the temperature goes over 300*C. . .

its drain cleaner though, it is like 93% to start with. I boiled it yesterday, and today I just heated it till it was fuming. 200c was an estimate, I have no idea how hot it got. Perhaps this was my problem, I'll try again tommorow.

[Edited on 2-6-2010 by Chainhit222]

hissingnoise - 2-6-2010 at 15:14

H2SO4 holds on to water tenaciously and only when SO3 fumes appear can you say it's ~98%. . .
As it cools it can be expected to absorb some H2O fron the air.
That makes getting the acid to 98% all the more necessary. . .

Jimmymajesty - 8-6-2010 at 12:41

As hissingnoise said, heat the sulphuric till you choke from the fumes, and your mom is yelling at you that you ruin the whole backyard:)

When it smokes intensely condense some of the fumes to a cold glass plate and touch it with some organic, like tissue paper, if the paper char, continue to contentrate it for further 15 minutes or more.

If I were to make 98% H2SO4 from ~90% drain opener, I would vacuum distill 1/3 of the acid and discard it.

For relatively contentrated nitric ~95% you do not need to use 98% sulphuric, baking flask, drying KNO3 etc, just start to distill over the HNO3 from the reaction mixture and discard the first 1/3 of it. or use it for something else that wont require cc nitric.

grndpndr - 8-6-2010 at 17:46

Have I been mistaken all this time despite company posts(info elsewhere) who specialize in reconstituting used H2SO4 that 93.3% is the maximum percentage available by heating alone.
Up to 70% little to no H2SO4 is lost, 85% and above is where the majority of H2SO4 vapor is lost to a maximum conncentration of 93.3% Above which simple heating will not increase.So my belief has been 98% by heating alone is a myth.
So if my drain cleaner S.G. indicates over 95% I consider myself lucky and use as is.The only thing I routinely boil is batt electrolyte for nitrations wher purity may be important.HNO3 for drain cleaner is a better use for a sulfuric acid contaminated with god knows though ive had may successful nitrations with drain cleaner.Beings electrolyte is about n the cleanest
H2SO4 I can lay my hands on its probably better used concentrated to 93% w/o impurities and compensating for the slightly lower concentration if needed in nitrations.Saving the possibly contaminated Drain cleaner for HNO3.
Back to the maximum concentration of H2so4 I believe thats dictated by the "azetrope of sulfuric acid/water system of 93.3%
at 338c" (Concentration of sulfuric acid and Its Application;QVF)
I think any chemist is aware of this the net is full of this easily unnderstood, easily available info.Some disagreement here but it is likely the way the ratios measured molar or % and altitude.
The current stuff(drain cleaner) liquid fire appears quite clean(light motor oil) and is 1.835 SP. Gr. 96%-98%? That I dont try to concentrate by any means.Most likely has impurities but none that have interferred as of yet w/mixed acids/nitric distillations.I usually have no use of anything over 68-70%HNO3
which makes dist easy.Even with my archaic retort light yellow HNO3, good enough-Fulminates/ nitrates the like.W/o air aspiration,urea.
[Edited on 9-6-2010 by grndpndr]

[Edited on 9-6-2010 by grndpndr]

agorot - 22-7-2010 at 19:08

I just posted a video to youtube where I made HNO3. watch it if you'd like. :D comments and criticisms welcome....I think I did the math right.

Contrabasso - 9-8-2010 at 06:18

Really odd values!

I've just assembled a branded quickfit apparatus to distil 35% nitric to get something closer to 65% at atmospheric pressure. Using a heating mantle the distillation temperature rose from 110 - 120C over a period of an hour and the process was stopped.
On cooling to room temp the SG of the distillate is about 1.10 and the SC of the residue is 1.35. Now considering that the original 35% acid had a SG around 1.23 I've definitely concentrated something but why is the residue the high SG product and the distillate the low SG remainder?

I have limited supplies of any sulphuric so I was hoping to reserve it for the final concentration past the azeotrope point.

Magpie - 9-8-2010 at 08:00

Your original acid is below the azeotropic concentration of 68% so the vapor condensed will be rich in water. When the distillate temperature reaches 120.5C your pot concentration is that of the azeotrope. Does this make sense?

See this excellent write-up:

The last page has the phase diagrams for the water/HNO3 system. It's been very helpful to me.

[Edited on 9-8-2010 by Magpie]

[Edited on 9-8-2010 by Magpie]

Contrabasso - 9-8-2010 at 08:40

Yes! Perfect sense, and it makes life easier too. Boil down to azeotrope, then run some conc sulphuric in and distil off the nitric.

Contrabasso - 13-8-2010 at 05:20

Does anyone care to tell me what vacuum is their choice for clean distillation of greater than azeotropic nitric? What temperature seem a good cross between clean processing and easy condensation using water?

Will a fridge compressor pull this vacuum or do I need better?

hissingnoise - 13-8-2010 at 05:55

What's wrong with the strength of HNO3 distilled from KNO3/H2SO4 at normal pressure?
Its concentration is sufficient to nitrate pentaerythritol and hexamine, so I can't see where the problem is. . .

Contrabasso - 13-8-2010 at 06:11

I have glass setup doing just that at the moment. All the product is seriously red/brown. I was hoping to make WFNA directly as locally sulphuric is a problem so I don't want to waste the reagents making and discarding the brown NOx.

Also I can buy 35% nitric easily so it should be possible to concentrate it (yes azeotrope I know!). The winchester of Sulphuric was a chance ebay lot, with a long drive to get it. Even stores that sell sulphuric drain cleaner elsewhere in the UK don't have it near me so I'd rather work on hydroponic nitric (35%) which just arrives by van simply for the buying it.

hissingnoise - 13-8-2010 at 06:54

The dissolved oxides can be removed (oxidised) by blowing dry air or better, dry oxygen, through your acid.
The last traces may be slow to disappear and a trace of added urea will finish the job.

uchiacon - 21-9-2010 at 20:08

Hey so I just bought a new aspirator to replace my old one. The old one was metallic, and since I was concentrating nitric acid in the distillation, it really didn't last a long time. I thought that I would be able to trap enough of the acid vapours in a vapour trap, but no such luck. As you can see in the picture, the nice nozzle that used to supply the vacuum is pretty corroded.

I got a 2nd hand glass aspirator, with a bit of what I assume is a leaf in the nozzle chamber. It doesnt effect the vacuum though I dont think. Got it for a great 40NZ or about $28US.
It uses a lot less water than the metal one, and it has enough of a vacuum in the nozzle chamber to make the water boil inside the aspirator, which is at about 12 degrees.

In a sealed setup, it can boil water at 25 degrees, and it might do it at 20 degrees, but I don't really know that as I havent tried to boil it at 20 degrees. I'd assume there is a way you can calculate this into mm/hg or PSI or kPa, but I don't really have a clue. It's about 1/4 of an atmoshphere that my aspirator is pulling right? I think it's a lot better than my metal aspirator, which could only boil water at 35 degrees C, but it takes a bit longer to evacuate the glassware. Seems to pull a better vacuum than the metal one too.

Could someone point me towards a page that has a good rundown on pressure? I've had a look on wiki, but I just end up getting a bit confused, the formula
Pressure = exp(20.389-5132/temp C) gives me a number with 185 zeros behind the decimal point of torr.

What am I doing wrong here?
I used a calculator on the internet, and it said that water will boil at 25C at 23.8torr/mmhg. Is this right?

Chainhit222 - 21-9-2010 at 21:01

Just use the sigma nomograph :

If waters normal bp is 100c, and you are getting it to boil at 25c, then your vacuum is 56mmhg.

[Edited on 22-9-2010 by Chainhit222]

nitric acid

cyanureeves - 22-9-2010 at 05:36

ive seen it done with mere glass coffee pot on B.B.Q. grill. with oil lamp tops used as condensing tubes and another coffee pot at opposite end.the more and wider the tubes the better it condenses. youll be surprised how much heat this glassware can tolerate.teflon tape was wound around the glass tubes and shoved into the mouth of the ( wire was wrapped around the smaller circumferance ends and used as flange rims to hold the glass set up tightly together. never saw the pressure build and push the apparatuses apart nor great amount of red fumes escaping but i do recall an annoying nose irritation upon standing close by.

uchiacon - 26-9-2010 at 00:20

guys, I was just doing a distillation. But after distilling 150mls of 70% HNO3 with 300ml of 99% H2SO4, I got a yield of 20mls, at which point nitric stopped coming over the still head and down the condenser.

The 20mls I did get was 95-96% concentration, burnt a small crater in my hand when a small droplet landed on part of the skin that the glove didnt protect. I didn't quite realize the potency of this acid until that happened lol.

20mls for 150mls isn't good enough for my liking. Can you guys diagnose the problem?

I use an aspirator to pull a vacuum in the setup I use. I have a 40cm liebig condenser that I use. The nitric acid I was distilling was boiling and coming over at around 70 degrees, and then it stopped boiling and then nitric acid seemed to stop evaporating, but I think 100mls of nitric acid has left the original nitric/sulfuric acid mix. Has this 100mls of acid or water just been sucked out by the aspirator? I think my joints are pretty tight, and I used 1 wrap of teflon tape to make them more airtight.

I didn't cool the condensated acid with ice, just water that was about 16 degrees.

Here's a vid I made a while back with a similar setup, except the aspirator was bigger than the small glass one I have now.

How should I go about reducing the amount of acid lost to the aspirator?

I also have a big 25L container of 70% nitric which I bought for $3/L, and I was hoping to use this up by concentrating it with the big 15L container I have of 99% sulfuric which I got at $2.75/L ;) ..... but would it just be better to distill nitric from scratch and have it concentrated that way? If it did it under vacuum, would it achieve a nice 90%+ conc of nitric?

[Edited on 04-07-09 by uchiacon]

Contrabasso - 26-9-2010 at 00:49

OK you should have 105ml but be satisfied at 100!

Firstly moderate the vacuum! While working at low pressure reduces the decomposition it also makes condensing the product much more difficult. If you want to use the aspirator then moderate the vacuum by adding a small air bleed into the vac line. Also cooling the condenser water may help. Where was the vapour condensing down the centre tube. It's best if the top quarter is vapour but the rest is condensing liquid, If the pressure is too low then the liquid in the receiver flask will evaporate too -Use an ice bath there too!

uchiacon - 27-9-2010 at 22:24

ok, well I did my second distillation today.

Instead of 20mls 95%, I got 90mls 96%.

Instead of using a 2:1 sulfuric/nitric acid mix, I used a 1:1 acid mix of 200mls each. I used 70% nitric and 99% sulfuric acids.

This time I cooled the receiving flask with ice and water. My 60cm liebig condenser had a decent amount of 14 C water going through it.

The acid mix began boiling at 45C, and it was still boiling with large bumps infrequently as I went to turn it off and remove the vacuum. At this point, the temperature had risen to 60 degrees C.

I did not notice a large amount of nitric acid in my aspirator vacuum tube, but there was maybe a few mls. It was flattened out because of the vacuum inside it.,

I'm still not satisfied with this yield, should I have let it boil longer? Should I reduce the vacuum?

Any help will be appreciated... thanks

Contrabasso - 28-9-2010 at 08:57

At 45c with a 14C condenser you are challenging distillation. You could well use cooler water (it will come with winter!) or better try to get the main boil at round 60c by moderating the vacuum.

Recycling H2SO4

experimenter - 7-11-2010 at 01:16

Hello everyone,

Reading some of your very informal posts, I was thinking of how one can recycle the sulfuric acid used in nitric acid production.

My idea is to use NH4NO3 + conc. sulfuric acid in excess to produce the nitric by distillation (as normal) and then heat the ammonium sulfate + conc. sulfuric acid residue (at ~290 degrees). By that way, one can release ammonia and sulfuric acid by decomposition of ammonium sulfate; the sulfuric acid stays in the flask.

What do you think, is it worth trying?

hissingnoise - 7-11-2010 at 03:16

Ammonium sulphate does dissociate at high temperature but its components, rather than separating, recombine on cooling - and so it is hard to take seriously the patent you cited . . .
Na and K nitrates with H2SO4 give more concentrated HNO3 than NH4NO3/H2SO4 and are preferred for this reason!

experimenter - 7-11-2010 at 05:33

Thanks for input.
As I see it in the patent, the ammonium sulfate is decomposed inside concentrated sulfuric acid. So, the sulfuric acid from the decomposition, is mixed with the existing acid while ammonia boils off, thus effectively separating those two substances (at least, this is how it is supposed to work).

hissingnoise - 7-11-2010 at 06:21

The reaction mentioned does occur to some degree but at a rate far too slow for practical purposes.
Also, hot, conc. H2SO4 is a potent oxidiser which can attack NH4, forming N2, H2O and SO2.
NH4NO3 and (NH4)2SO4 in aqueous solution @>100*C evolve traces of NH3.
(NH4)2SO4 is reduced to the bisulphate and the nitrate becomes increasingly acidic but at an almost immeasurably slow rate.
BTW, the patent itself contains a peppering of misspellings, making it a bit unusual . . .

experimenter - 7-11-2010 at 08:23


The reaction mentioned does occur to some degree but at a rate far too slow for practical purposes.

Yes, the possible low speed of the reaction is my major concern also. Also, probably there will be some contamination in the acid from the various decomposition products.

experimenter - 7-11-2010 at 09:43


Na and K nitrates with H2SO4 give more concentrated HNO3 than NH4NO3/H2SO4 and are preferred for this reason!

Can ammonium nitrate give azeotropic (68%) HNO3? I plan to dissolve the required NH4NO3 in hot H2SO4/water solution. Also, in order to avoid decomposition of NH4NO3, I plan to distill the acid in vacuum.

hissingnoise - 7-11-2010 at 09:54

NaNO3 gives good yields of HNO3 @ normal pressure!
The NaHSO4 you're left with is more useful than (NH4)2SO4 . . .

experimenter - 7-11-2010 at 12:04


The NaHSO4 you're left with is more useful than (NH4)2SO4 . . .

Why? Can I make sulfuric acid from that?

hissingnoise - 7-11-2010 at 12:50

Well yes, as it happens, you can - if you have the determination . . .

Rosco Bodine - 7-11-2010 at 14:21

Some of the strategy known as UTFSE would have led to knowledge that it is the bisulfate of ammonia NH4HSO4, not the normal sulfate of ammonia (NH4)2SO4, which is the byproduct of HNO3 synthesis using NH4NO3 + H2SO4. Heating the ammonium bisulfate results in dehydration to ammonium pyrosulfate.

To get a normal sulfate byproduct from the reation of a nitrate and H2SO4, a nitrate must be selected which does not form an acid sulfate. Aluminum nitrate is one example. Such a reaction leads to a twice greater yield of HNO3, per mole of H2SO4, since both of the acid hydrogens of the H2SO4 are then used to form HNO3, rather than the usual one acid hydrogen which remains with an acid sulfate byproduct.

experimenter - 7-11-2010 at 23:52

Thanks for correcting me.
What is pyrosulfate? Is it the same as ammonium persulfate, (NH4)2S2O8? In wikipedia it says that it decomposes at 120 °C. In what substances does it decompose?

hissingnoise - 8-11-2010 at 03:34

Thanks for correcting me.

And me!
I was under the impression that NH4HSO4 in H2SO4 readily converted to the normal sulphate @~60*C and that the corresponding reaction with NaHSO4 was slow @ >125*C!
Oh well . . .
Anyway, persulphates are salts of peroxydisulphuric acid H2S2O8.
Ammonium persulphate decomposition produces a range of products which includes ozone and NO2.
Sodium pyrosulphate (Na2S2O7) thermally decomposes to Na2SO4 + SO3.

[Edited on 8-11-2010 by hissingnoise]

experimenter - 8-11-2010 at 07:56

Ammonium pyrosulfate: (NH4)2S2O7 (ref pyrosulfate)
Ammonium persulfate: (NH4)2S2O8 (ref

Anyway, I don't think I need to mess with them. I will just try to decompose the salt that remains after the distillation inside sulfuric acid and see what happens.

I already have done the NH4NO3 + sulfuric acid distillation (which by the way seems to run smoothly even without vacuum) and left with the icy, stone-like salt. It melts easily.

hissingnoise - 8-11-2010 at 08:14

I will just try to decompose the salt that remains after the distillation inside sulfuric acid and see what happens.

Well, good luck with that . . .

experimenter - 8-11-2010 at 10:39


Well, good luck with that . . .


Just tried it, it doesn't work. I couldn't detect any ammonia evolving either by nose or by ph paper before the decomposition of the sulfuric acid.

hissingnoise - 8-11-2010 at 10:56

See! Seeee! I told you it wouldn't work, didn't I; Didn't I? Oh but would you listen? Would you???
No! You had to go and be an experimenter. :):D;):P

experimenter - 8-11-2010 at 11:19

Hehe, yeea! :D
I'm an experimenter, can't help it... :P

hissingnoise - 8-11-2010 at 12:56

One should discard all advice out-of-hand without, however, giving the impression the decision was taken lightly . . .

Zinc - 22-11-2010 at 11:26

Does anyone know how much water should be added to a AN/H2SO4 mix so that azeotropic HNO3 can be distilled from the mix instead of the conc. HNO3?

I think perhaps if the amount of AN/H2SO4 is what is required to produce 100 g of HNO3, 32g of water should be added?

Rosco Bodine - 22-11-2010 at 19:14

Distilling azeotropic nitric from H2SO4 + NH4NO3 or other nitrates, is a good process for making use of cheap battery electrolyte as the contributor of needed water, to reduce the requirement for use exclusively of concentrated H2SO4, thereafter diluted with H2O. To find the theoretical minimum requirement of water
for producing the 68% HNO3 azeotrope, first multiply the theoretical grams of pure HNO3 expected from a given mixture by the reciprocal of 0.68, ( which is 1.47 ) subtracting the weight of the expected weight of pure HNO3 from the product to give the minimum required H2O.

For example:

For a balanced reaction equation expected to produce 100 grams pure HNO3
100 X 1.47 = 147 = (total weight of 68% azeotrope produced) - 100 (total weight of pure HNO3 contained in the 147 grams of azeotrope) = 47 grams (total H2O contained in the 147 grams of azeotrope)

In reality a bit in excess of the theoretical requirement of H2O will actually be needed and a bit in excess of the theoretical requirement of H2SO4 also,
with respect to theory based upon nitrate, and the initial distillate of HNO3
will be more concentrated than the azeotrope, but the distillate will gradually rise in temperature towards the azeotrope which will be the largest fraction.

Funkerman23 - 5-3-2012 at 17:14

Only thing that is missing from this thread is the kitchen sink..Still..If Nitric acid will react with platinum and gold( albeit very very slowly) then at what rate will it attack borosilicate glass?

[Edited on 6-3-2012 by Funkerman23]

Bot0nist - 5-3-2012 at 19:14

From a practical standpoint, nothing observed. I have stored RFNA in boro for quite some time, and never had problems at all. My distillation gear used in its synthesis is also good as new.

CaliusOptimus - 22-1-2013 at 02:19

Just wanted to share my recent experience with RFNA purification:

500mL RFNA distilled from 98% tech H2SO4 and oven-dried KNO3 was placed into 1000mL RBF. Gas dispersion tube in one neck, condenser (-10c) on another. Condenser was connected to a gas adapter>NaOH wash bottle>outside. Tech grade compressed O2 was fed through dispersion tube for 8 hours while the RBF was warmed to 50C. I didn't notice any loss of color from the starting acid, in fact I'd say it got darker.

Next day I hooked a fish tank pump to the gas dispersion tube, with a 12" long 3/4" ID CaCl2 drying tube spliced in the line. In a matter of ~8 hours the acid went from dark red to water white. I've come to the conclusion that my acid was too anhydrous to run pure O2 and expect results. I figure that whatever water made it past the CaCl2 tube must have been enough to facilitate the reaction.

I won't be wasting any more O2, and I may not even dry the nitrate again. Both things have seemed to draw out the process with no real benefit.... but I should probably titrate my HNO3 before I say any more.

[Edited on 22-1-2013 by CaliusOptimus]

Cheap and Effective Nitric Acid Distillation Apparatus

Hennig Brand - 30-6-2014 at 12:03

Here is a very simple little glass still I made a year or so ago from common flasks without ground glass joints. The most important part of the apparatus is the Teflon bushing, which can be easily made on a lathe from Teflon round stock of an appropriate diameter. Two approximately eight dollar flasks were used and a piece of glass tubing obtained for free. A piece of Teflon round stock was purchased for $30 which provided enough material for 4 bushings. The center hole of the bushing was bored out slightly oversized and the outside diameter of the section which would slide into the flask was made slightly undersized. This allowed the glass tubing and outer diameter of the bushing to have many wraps of Teflon tape applied so as to give some of the elasticity that would normally be present if a rubber stopper was used and provide a better seal. Experiments showed that the bushing still tended to rise slightly, once the flask got hot, allowing vapor to escape. This was easily solved by applying a few wraps of black electricians tape, to the top of the flask and bushing, which completely solved the problem. The first picture of the apparatus in use is from early spring when temperatures where near freezing and with slow distillation air cooling was adequate. The second picture is from a hot day this summer and the receiving flask was placed in an ice bath. I have ideas for how one of those little $10-12 centrifugal table top fountain pumps could be used to pump the water, or iced water up, over the round bottom flask receiver if extra condensing power was needed.

A steel file may be needed to score the tubing if it needs to be made shorter. A propane torch is needed to heat the tubing so that it can be bent and then annealed.

Teflon Bushing Top View.jpg - 298kB Teflon Bushing Bottom View.jpg - 325kB HNO3 Distillation Cold Day in Spring.jpg - 227kB HNO3 Distillation Hot Day in Summer.jpg - 267kB

BTW, I do have a ground glass distillation apparatus, but just for fun and skill development I wanted to build this one.

I probably should have another stopper, a two hole, in the round bottom receiving flask. A smaller diameter piece of glass tubing could extent out of it increasing the cold surface area and acting as an air cooled reflux condenser. This would help reduce the amount of escaping nitric acid vapor as well as probably reduce the amount of absorption of moisture by the nitric acid.

[Edited on 30-6-2014 by Hennig Brand]

PHILOU Zrealone - 1-7-2014 at 08:24

Same can be done with a glass alembic or a glass retort...back to alchemistry :D

It cost about 8-15€ to get one (250-500 ml) with a glass roded stopper for easier filling.

Hennig Brand - 1-7-2014 at 09:36

Simple is often better. ;)

I always wanted one of those, and actually spent some time looking in the past, but never found one for a good deal here in Canada. I think it would cost me closer to $100 by the time I had one of those little glass retorts in my hands and there would be shipping time as well. I think what I have built is actually better (for me) in many respects, however, with the first being that it can be easily built by just about anyone with commonly available materials. The Teflon will likely have to be ordered, but it is still readily available. It is a very trivial matter to make the Teflon bushing on a lathe, or have someone do it who has access to a lathe. The boiling flask is 1L and it cost $8. With the exception of the glass tubing the apparatus is quite robust and if the tubing breaks it is a trivial matter to replace it. Not much could be done if one of those old fashioned retorts got a crack, or something, unless you are good with glass or know someone who is.

Also, the glass delivery tube could easily be turned into a Liebig condenser (tube in tube) if that was desired. The water jacket could be made of just about anything you wanted (plastic plumbing pipe, etc), because it would not be exposed to nitric acid and nitric oxides only cooling water.

Just realized the following thread may have been a more appropriate place to post what I did.

I was thinking too, it really is a lot of fun and can provide a lot of satisfaction to make your own equipment. Many people, who haven't developed those skills, would find it very difficult to make their own equipment, if for some reason the commercial supplies were no longer accessible to them.

[Edited on 2-7-2014 by Hennig Brand]

Refinery - 31-7-2014 at 11:06

Can one make nitric acid from a nitrate salt and formic acid? In theory, formic acid and (ammonium) nitrate could form ammonium formate and nitric acid, but is the reaction balance high enough to proceed? Whether this process works or not, one must remember that ammonium formate and formamide will form hydrogen cyanide if heated too strongly, so a water bath or other medium should be used, or gasses led away safely.

I have made nitric acid with sulfuric acid and ammonium nitrate many times with normal glass distilling setup. Nitrates are somewhat available, but the purification is a little itchy process, because there are lots of soluble impurities which must be saturated out and there will always be losses. Farming grade nitrates are a lot more sensible, but I can get only customer stuff which is very diluted, way under 50% in weight AN. Sulfates wont matter with sulfuric acid method, but with other methods they do.

I have also been looking this way to convert ammonium nitrate into nitric acid without sulfuric acid. I discussed about this in another topic, but shortly explained, one should get calcium hydroxide and ammonium nitrate and mix equimolar amounts in water and heat strongly up to boil, and ammonia gas is formed which is recovered in cold water. The solution now contains calcium nitrate, calcium hydroxide, and filtering is not quite necessary for the next step, if there is excess CaOH, let it be there. Nonetheless they both are very insoluble to water. In this phase the purity of AN is very important. If it contains potassium or sodium sulfate, there will be reaction with calcium nitrate and this sulfate, forming very insoluble calcium sulfate(gypsum!) and corresponding nitrate. Yes, one can filter this out too, but in the next step it will be a big danger.

One must now boil off the water from the calcium nitrate. If it contains CaOH, it doesn't matter, because now the Ca(NO3)2 is put into steel pot and heated to over 650C, and now it will start to release lots of NO2 gas. This gas forms HNO3 with contact on water. The yield suffers at least 1/3 because part of the nitrogen is turned into monoxide and it is probably lost. If in this heating phase the nitrate contains ammonium, potassium or sodium nitrate, serious danger will come upon the chemist, because calcium nitrate decomposes controllably but K, Na and especially AN will form major risk. The nitric acid formed can be concentrated up to 68% by distilling, and further concentrated as high as WFNA with conc. sulfuric acid(which can be reactivated by boiling off the water). All is left in the reactor is calcium oxide, and if any CaOH is left in there, it will just decompose into water and calcium oxide as well, so purification is not needed in the Ca(NO3)2 conversion phase.

Pro is that all one needs is slaked lime and some purified AN, con is that it needs a bit of specialty equipment, but this shouldn't come as trouble for few hundred bucks at maximum if this is someone's hobby, people put thousands into cars and other stuff I dont like at all. Decomp temp could be lowered with magnesium or even copper nitrate(not 100% sure about this so check if gonna do anything!) and it could even be possible to use glass distilling setup to pyrolyze these two.

Classic method is of course the Ostwald where oxygen and ammonia is fed through a cat at intermediate pressures(some 4-10 bars). One could use ordinary air comp and bottled or cryogenized liquid ammonia in order to control the feed. Ideally the cat tube should be made from thick quartz so the chemist can observe the feed rate and temperature, but afaik this reaction produces very much residual heat which could even melt the cat and the tube as well so cooling may be needed. It is cited in this topic before that too low pressure and feed rate will form mostly nitrogen gas, while too fast rate would leave ammonia unreacted, and this could react with nitric oxides, or worst case, the nitric acid formed in the receiving tank. In general this app uses copper or preferably platinum group cat heated up to 600-900C, and a middle tank where the reaction between nitric oxide and oxygen happens to form nitrogen dioxide, which is led through into receiving tank partially filled with cold water, forming nitric acid and nitric oxide.

I think this reaction is something that only the most determined chemists would want to engage because the reaction apparatus would be quite complex and somewhat expensive even when made by oneself with good quality welder. And even a small app with normal carage compressors $99 at wal-mart could be fine-tuned and the flow rates optimized in order to make it to produce hefty amounts of nitric acid in quite small time frame, like hundreds or even thousands of liters. Ammonia gas itself is quite available by lime(sold like quarter a buck per kg) hydrolysis of urea(under a buck per kg in pallets) and it can be stored in normal(BBQ) steel flasks, either condensed with compressor, refrigerant apparatus or dry ice. A tabletop reactor app with palm-sized pumps and stuff would be nice one, though, as did the Mr. Haber did in the 19th's to prove his process.

aga - 31-7-2014 at 11:47

Wow ! Litres !

I was quite pleased when i made sodium nitrate from fertilizer, recrystallised it, then distilled with sulphuric acid to get ..... 30ml nitric

Refinery - 31-7-2014 at 13:36

It's just about the amounts, to certain extent. :) I have several larger flasks, largest one is 4 liters, but I rarely perform any synthesis involving aggressive chemicals on that large scale. Largest I've done on ammonium nitrate and sulfuric acid in a single batch was about 800ml of RFNA output. I apologize if the amounts seem large to some users here but I've got used to measure bulk stuff in metric tons and delicate ones in liters because I work in petrochemical industry operations. :)

Extra cautions must be taken with larger amounts, naturally. I've prepared my working environment and PP equipment according to the amounts I work with, usually with the worst case scenario in mind, which is, blowing up the reaction vessel.

Manifest - 31-7-2014 at 13:54

I just ran some numbers and to get 10ml of 100% nitric acid you would use 25ml of Sulfuric Acid and 25 grams of Potassium Nitrate.
Of course you are not going to get a 100% concentration.

aga - 1-8-2014 at 14:17

Quote: Originally posted by Refinery  
Largest I've done on ammonium nitrate and sulfuric acid in a single batch was about 800ml of RFNA output


My distilled NA F'ed White fumes (a bit like steam/dry ice)
The liquid was Orange.
Does that make it OFNA, WFNA or RFNA ?

@Manifest : i'll do it again and record the details. Only did it once with no measurements at all.
Would it end up 100% if it were done under hard vacuum, or is conc sulphuric likely to let go of water in vacuum ?

(note to self : google what 'hard vacuum' actually means, despite it sounding good, and then find out if i can even do that on this planet)

[Edited on 1-8-2014 by aga]

TheChemiKid - 1-8-2014 at 14:20

That makes it WFNA with NOx dissolved in it, if you vacuum distilled it, you could get it more pure.

aga - 1-8-2014 at 14:57

so if i hook up the vac pump it gets more Clear ?

NaOH trap for the punp ?

Zyklon-A - 1-8-2014 at 18:20

I don't think you could get it to 100%, even with a good vacuum.
IIRC, You can bubble dry oxygen (air should work too) through RFNA or WFNA with dissolved NO2 to make clear, more concentrated nitric acid.
I know this works with ozone, and I'm pretty sure just oxygen will do it too - albeit much slower.
Absorbtion of Nitrous Gasses is a great book, with an incredible amount of info on all nitrogen oxides and oxiacids.

[Edited on 2-8-2014 by Zyklon-A]

PHILOU Zrealone - 5-8-2014 at 10:25

Quote: Originally posted by Refinery  
Can one make nitric acid from a nitrate salt and formic acid? In theory, formic acid and (ammonium) nitrate could form ammonium formate and nitric acid, but is the reaction balance high enough to proceed? Whether this process works or not, one must remember that ammonium formate and formamide will form hydrogen cyanide if heated too strongly, so a water bath or other medium should be used, or gasses led away safely.

One must now boil off the water from the calcium nitrate. If it contains CaOH, it doesn't matter, because now the Ca(NO3)2 is put into steel pot and heated to over 650C, and now it will start to release lots of NO2 gas. This gas forms HNO3 with contact on water. The yield suffers at least 1/3 because part of the nitrogen is turned into monoxide and it is probably lost.

About the first part:
1°)HNO3 is about 500.000 times more acidic than HCO2H.
So the reaction will only proceed as traces.

2°)Formic acid doesn't stand HNO3 well because it is a reducer and HNO3 is a strong oxydiser.
5 HCO2H + 2 HNO3 --> 5 CO2 + 6 H2O + N2
I think even that stoechimetric mix of 100% HNO3 and 100% formic acid could be detonable...
HNO3 100% forms sensitive detonable mixtures with many solvents like glacial acetic acid, benzene, toluene, nitromethane, aceton, acetonitrile,...

3°)I wouldn't trust the heating of an intimate mix of an organic matter (formic acid, ammonium formate, formamide, cyanic acid or ammonium cyanide) with NH4NO3 and traces of HNO3.

About the second part:
Nitrogen monoxyde (NO) can be recovered by recirculation with air...the reaction is spontaneous. Colourless NO turns immediately red when in contact with air...
2 N=O + O2 --> 2 NO2 <==> N2O4
Same will probably happen with H2O2:
N=O + H2O2 --> H2O + NO2

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