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Author: Subject: Making Nitric acid!

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cool.gif posted on 28-7-2015 at 00:56
Making Nitric acid!

I am about to synthesize some 68%(w/v) azeotrophic nitric acid, is there anything I would have to watch out for? :cool:
Here's the method I am going for:
KNO3 + H2SO4 --> HNO3 + KHSO4.
I will also distill the product for higher purity.

Here are a few videos for reference. (5:01 onwards)
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[*] posted on 28-7-2015 at 01:33

Doug Nurdrage and NileRed are (I think) all members here. All three produce videos that are generally very sound. All three are highly experienced. And I have watched all three of these in the past. (I'll tefrain from another watching right now.)

This means that you can follow their procedures with some confidence.

Be aware of all the things that you don't see in the video - the note paper with stoichiometric calculations, the safety glasses, the junk that has been cleared off the work bench, the mop up kit with sufficient weak base and water, the cleaning cloths, gloves, fume hood, clear route to the door and so on. Conc nitric is nothing to be trifked with. Start with small quantitied for your first run.

Also read here. There is a wealth of information and experience (and not much of it from me.) It's all a mere search away. Board protocol is to add to an existing thread rather than start a new one. And also to put this kind of enquiry in Beginnings.

Welcome to SM.
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28-7-2015 at 23:08

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[*] posted on 5-6-2016 at 15:17

I'm sure there is already a list I've missed. I've lurked a long time and decided to materialize because I simply wanted to congratulate and thank all of you for keeping this kind of thing alive despite the phobics trying to ban or silence anything which makes them uncomfortable. For me it makes being feel less isolated. I wonder if there is any list of people who make the best of the chem, experimental, scientific etc channels out there. I'd love to reach through the monitor and shake the hands of the creators of the best of them. (the post above mentioned both Doug Nurdrage and NileRed who are two of my newfound favorites - pass along that I think they're terrific!)

p.s. today I'm following the footsteps of those ahead of me of those who want the conc HNO3 I guess because they enjoy the yellow-orange scar tissue you get from it in organic!
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National Hazard

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[*] posted on 5-6-2016 at 16:19

Something else that isn't widely mentioned in videos:

Be aware that some thermometer adapter seals can be degraded severely by the HNO3 vapours. I had it happen to me once and it took me a long time to find the leak, until it punched me in the nose (quite literally).
Now I seal the adapter with PTFE tape, which I suggest you do too, unless the existing seal is resistant to Nitric Acid.

"The chemists are a strange class of mortals, impelled by an almost insane impulse to seek their pleasures amid smoke and vapor, soot and flame, poisons and poverty; yet among all these evils I seem to live so sweetly that may I die if I were to change places with the Persian king" - Johann Joachim Becher, 1635 to 1682.
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[*] posted on 6-6-2016 at 03:23

Having prepared HNO3, the next task is to keep it stable (brown glass bottle, cold,...). Chemistry related comments I previously made may be of assistance. To quote:

"When boiling in light, even at room temperature, there is a partial decomposition with the formation of nitrogen dioxide following the reaction:

4HNO3 → 2H2O + 4NO2 + O2 (72°C)

which means that anhydrous nitric acid should be stored below 0°C to avoid decomposition."

Also, in aqueous solution, it readily ionizes into the nitrate ion NO3− and a hydrated proton (hydronium ion) H3O+ :

HNO3 + H2O → H3O+ + NO3-

Now, combine the above reaction with some radical based chemistry introduced by exposure to heat, light, solvated electrons, radiation,... could proceed as follows:

HNO3 + M ⇌ ·OH + ·NO2 + M (see )
NO3− + ·OH = ·NO3 + OH-
·NO3 + ·NO2 = N2O5 (see )
N2O5 → N2O4 + 1/2 O2 (assumes full completion of action of 1/2 O2 + NO to NO2 whose reaction speed declines with increasing temperature)

Reference: See

The approximate implied net reaction by direct summation of the above:

2 HNO3 + H2O → H2O + H+ + OH- + N2O4 + 1/2 O2

Or equivalently:

2 HNO3 → H2O + N2O4 + 1/2 O2

which is a generally cited decomposition reaction and actually has been confirmed by investigations of the self decomposition reaction of HNO3 in the liquid phase between room temperature and 80 C and also in the gas phase to 475 C. Reference:
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[*] posted on 6-6-2016 at 06:01

The issues, mentioned by AJKOER, only occur at very high concentration of the acid. I have 70% HNO3 in a clear colorless glass bottle which is stored in a cabinet, exposed to diffuse daylight. There is no continued decomposition of the HNO3. The acid is very pale yellow, nearly colorless (see this Wikipedia picture of my acid):

I keep the acid around and use it very sparingly at the moment. Restocking nitric acid is impossible nowadays, buying NH4NO3 also is impossible nowadays, and buying KNO3 or NaNO3 is becoming more and more difficult. I soon intend to test a method, based on decomposition of sodium nitrite (used as the cheap food additive E250 and easy to obtain at 99+% food-grade purity) in dilute acid and leading the NOx through water, together with air. I hope that the method will be useful for making somewhat more concentrated nitric acid. In theory it should, how it works in practice is yet to be found out.

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