Sciencemadness Discussion Board

My nitric acid experiment worked, then failed

Booze - 23-3-2017 at 15:22

So I used the method Nile Red did. It was going exactly as planned, until the very end of the distillaton. So No2 gas was produced from my distillate (nitric acid) and the gas traveled back into the boiling flask, and it is still there. I had a sodium hydroxide trap if any no2 escaped, and it did kill the gas. But what happened was it created a vacuum and sucked the sodium hydroxide into my nitric acid (boo-hoo). So now can someone tell my why that happened, and how do can I take apart my aparatus without releasing the nitrogen dioxide? Thanks. The end of my project really scared me.

XeonTheMGPony - 23-3-2017 at 16:01

take it apart and don't worry to much about the small amounts of it, open a window or a fan helps too short of huffing it direct from unit you'll be well enough.

then dry out and recover your fresh sodium nitrate!

In the future: Use a check valve or put the water trap lower down and use the force of gravity as the check valve!

Texium - 23-3-2017 at 16:09

Attaching an inverted funnel to your gas outlet will also prevent suckback.

A Halogenated Substance - 23-3-2017 at 16:21

If you really want you, you could also create a suckback trap in the form of an empty vessel that is connected between the gas trap and the receiving flask. That way, if suckback does occur, it doesn't ruin your product.

After suckback occurs just replenish the gas trap. :)

Booze - 23-3-2017 at 18:52

Okay, I fixed the problem, but I can smell a slight fixation of nitrogen dioxide. Should I be worried? I can see it in my apparatus, but not outside of it. It burned my lungs when I took apart the apparatus for the first batch I made.

XeonTheMGPony - 23-3-2017 at 19:00

that would be a bit of nitric acid vapors, need more air flow in the room slight smell is in safe small concentrations.

Providing the volume was less then a small soup cans worth your quite safe.

Tsjerk - 23-3-2017 at 23:00

Check the gas trap part of figure 1 in this link, that would nicely prevent suck back.

http://orgsyn.org/demo.aspx?prep=cv9p0281

Melgar - 24-3-2017 at 05:55

What happened is called "suck-back", and it happens when an apparatus filled with hot gas contacts a liquid that can cool it to its liquid form. The gas all condenses on the liquid at once, lowering the pressure in the apparatus, and pulling more of the lower temperature liquid with it. The double-whammy is when there's an extremely exothermic reaction between the liquid that was pulled in, and the liquid in your flask. Hence, the reason you should always be very, very careful when using sulfuric acid as a moisture trap. You need those check (one-way) valves, which are pretty cheap on eBay. The HHO-powered car people are actually good for something after all, it seems, since they're the main ones buying and selling chemical-resistant plastic check valves.

Booze - 24-3-2017 at 07:12

Quote: Originally posted by Tsjerk  
Check the gas trap part of figure 1 in this link, that would nicely prevent suck back.

http://orgsyn.org/demo.aspx?prep=cv9p0281

Yes, I did do a version of that. I should re do it though because I poorly sealed it.

Booze - 24-3-2017 at 07:14

Quote: Originally posted by Melgar  
What happened is called "suck-back", and it happens when an apparatus filled with hot gas contacts a liquid that can cool it to its liquid form. The gas all condenses on the liquid at once, lowering the pressure in the apparatus, and pulling more of the lower temperature liquid with it. The double-whammy is when there's an extremely exothermic reaction between the liquid that was pulled in, and the liquid in your flask. Hence, the reason you should always be very, very careful when using sulfuric acid as a moisture trap. You need those check (one-way) valves, which are pretty cheap on eBay. The HHO-powered car people are actually good for something after all, it seems, since they're the main ones buying and selling chemical-resistant plastic check valves.

I don't think that is what happened. Right when I turned off my bunsen burner, no2 gas travelled from the distillate flask back up the condenser and into my boiling flask.

Melgar - 24-3-2017 at 07:23

Quote: Originally posted by Booze  
I don't think that is what happened. Right when I turned off my bunsen burner, no2 gas travelled from the distillate flask back up the condenser and into my boiling flask.

Oh, you mean all you lost was a bit of NOx gas? Well that would just be from the gas condensing on the inside of the apparatus when it cooled off, and is pretty much inevitable. Just open it outside or something; if you get a whiff of it, you'll probably notice it smells like truck exhaust. I don't know who Nile Red is or how he makes nitric acid, but if you're using the sulfuric acid + nitrate salt route, and generally want to reduce the brown fumes, you can either pull a higher vacuum so the distillate comes over at a lower temperature, or you can add some hydrogen peroxide to your sulfuric acid first, which will both get it hot, and oxidize any NOx species into nitric acid. I used to use this method all the time to make white fuming nitric acid.

[Edited on 3/24/17 by Melgar]

Booze - 24-3-2017 at 08:32

Quote: Originally posted by Melgar  
Quote: Originally posted by Booze  
I don't think that is what happened. Right when I turned off my bunsen burner, no2 gas travelled from the distillate flask back up the condenser and into my boiling flask.

Oh, you mean all you lost was a bit of NOx gas? Well that would just be from the gas condensing on the inside of the apparatus when it cooled off, and is pretty much inevitable. Just open it outside or something; if you get a whiff of it, you'll probably notice it smells like truck exhaust. I don't know who Nile Red is or how he makes nitric acid, but if you're using the sulfuric acid + nitrate salt route, and generally want to reduce the brown fumes, you can either pull a higher vacuum so the distillate comes over at a lower temperature, or you can add some hydrogen peroxide to your sulfuric acid first, which will both get it hot, and oxidize any NOx species into nitric acid. I used to use this method all the time to make white fuming nitric acid.

[Edited on 3/24/17 by Melgar]



Okay... I don't have a vacuum pump, but Nile Red is a youtuber and he uses KNO3, H2SO4, and water then distills that mixture. He also did 404 grams KNO3, 200 mL water, and 202 mL sulphuric acid drain cleaner. I did smell some nitrogen dioxide, and it burned my nose. I just want to be as safe as possible and try to get rid of much of it as I can.

Melgar - 24-3-2017 at 16:00

Quote: Originally posted by Booze  
Okay... I don't have a vacuum pump, but Nile Red is a youtuber and he uses KNO3, H2SO4, and water then distills that mixture. He also did 404 grams KNO3, 200 mL water, and 202 mL sulphuric acid drain cleaner. I did smell some nitrogen dioxide, and it burned my nose. I just want to be as safe as possible and try to get rid of much of it as I can.

In that case, he made nitric acid the same way everyone else does, which is good because I have lots of experience with that route. I never had a vacuum pump either, but you can pull a full vacuum just with a brake line bleeder. They look like this:

http://www.scooterhelp.com/genmaintain/brake.bleed.tool.jpg

and they can pull a better vacuum than most vacuum pumps. They only cost maybe $20, and if someone is stupid enough to let you borrow theirs for distilling nitric acid, it's a common tool to own. I've ruined like three or four, because vapors got in them, but if you use a decent check valve AND a vapor trap with an alkaline solution in it, you'd probably be okay. The check valve can even go after the vapor trap, and can even be substituted with a manual on/off valve if you remember to always leave it off when you're not checking pressure or trying to pull a higher vacuum. However you can't just use one or the other, using both is essential.

As far as breathing it in, it's an acute hazard, mainly. That is, small amounts of it won't do any sort of damage that your body can't repair. Like most other acid vapors, it would cause you intense discomfort at MUCH lower levels than it would take to do any long-term damage to you. That said, the intense discomfort would probably persist for a day or so, and you'd learn to be more careful with nitric acid vapors. :P

edit: The other hazard is accidentally corroding anything metal in the room, so if possible, it's a good idea to have ventilation.

[Edited on 3/25/17 by Melgar]

XeonTheMGPony - 24-3-2017 at 20:01

That particular run is making 68% nitric, I normally make fuming but for some upcoming stuff I needed azeotropic, so I followed his method: https://www.youtube.com/watch?v=KBeo8nww21g

For those in Canada wally world has a brand of CaN/AN (Equate) cold pack which is perfect for this, as just add a minimum straight ammonia water to it, filter out the CaOH and then add to your flask, heat till no more ammonia smell and ready to rock!

Safe the Ammonium Sulfate crystals for projects requiring NH3!

It requires a secondary fractional distillation to get the final azeotrope, or very care full simple distillation.

Any NO2 fumes will be from over heating of the final mass in the boiling side, they just aren't visible till it cools.





[Edited on 25-3-2017 by XeonTheMGPony]

PirateDocBrown - 25-3-2017 at 02:52

Quote: Originally posted by Melgar  

As far as breathing it in, it's an acute hazard, mainly. That is, small amounts of it won't do any sort of damage that your body can't repair. Like most other acid vapors, it would cause you intense discomfort at MUCH lower levels than it would take to do any long-term damage to you. That said, the intense discomfort would probably persist for a day or so, and you'd learn to be more careful with nitric acid vapors. :P


That's not true at all. NO2 is insidious and can kill you without you even knowing that it's happening.

It is entirely possible to be breathing an undetectably low level of NO2 for a few hours, then have several days pass, and then die of irreversible pulmonary edema. Levels high enough for discomfort are good, because at least then you know to leave!

Always ventilate if there's NO2 possible. Stay away from it as much as you can. It can cause permanent lung damage, even if you live.

XeonTheMGPony - 25-3-2017 at 05:33

you'd need industrial levels of exposure for that to even be a consideration of a risk. You are very correct about the mechanism and the delayed action just the estimation of the exposure you are exaggerating a bit much (Good safety practices will keep you alive and healthy)

A guy with a simple and small distillation rig (2L) would have to huff the fumes directly to get the required dose at the needed concentration to even have to worry about the possibility of that!

(Less fume exposure the better for sure)

There is being safe, then there is being paranoid, being scared of a substance is more dangerous then understanding and respecting it with well reasoned thought.

But when dealing with ANY acid that can fume, good air flow is pertinent, exhausting fan even better as it ups the safety margins and makes working with them allot more comfortable.
(Ok and healthier in the long run but you never escape life alive!)

When I do my Acids I use a light vacuum powered by an aspirator and a circulating water bucket to sequester the fumes, once don I simply break apart the aperatus with out any concern as the dosage and concentration are low enough to at worst cause mild discomfort, I rather like the smell of the residual NO2, shame it is a forbidden scent to be enjoyed!

One most keep things in proportion to reality of the nature of the substance.

SO again, all he needs is an open window or a fan when doing and taking apart his set up, he all ready properly scrubbed the vented fumes.

() = Additions

[Edited on 25-3-2017 by XeonTheMGPony]

Melgar - 25-3-2017 at 11:06

Quote: Originally posted by PirateDocBrown  
That's not true at all. NO2 is insidious and can kill you without you even knowing that it's happening.

It is entirely possible to be breathing an undetectably low level of NO2 for a few hours, then have several days pass, and then die of irreversible pulmonary edema. Levels high enough for discomfort are good, because at least then you know to leave!

This is virtually impossible outside of an industrial setting, and I'm sure you know enough to realize that. OP has a healthy fear already, we don't want to scare the shit out of him over quantities of a substance that we can probably both agree are not going to kill him or do any sort of long-term damage. My point was to tell him, relax, yes it's scary and dangerous, but it's not plutonium. Turning up the fear dial to 11 for every dangerous substance makes people less afraid of the TRULY dangerous substances like dimethylmercury, dimethyl sulfate, phosgene, etc.

Booze - 26-3-2017 at 12:11

Okay, I feel much better about No2. I work in my garage with the big door open, any fumes that are produced will be gone in a matter of seconds. I let all of the No2 escape outside my simple distillation before I take it apart. I don't really see a need for a vacuum, so I won't bother with getting any brake lines.

XeonTheMGPony - 26-3-2017 at 13:50

then you have nothing to worry about, You'd literally have to suck on it to get a dangerous amount in your system(Body) in such a situation!

[Edited on 26-3-2017 by XeonTheMGPony]

clearly_not_atara - 26-3-2017 at 14:29

I think that unsophisticated people especially are fond of telling tall tales about toxicity, as I've seen a number of scary stories on photography forums about nitrogen dioxide (a common decomposition/side product of AgNO3) which don't really correspond to what I understand about its toxicity, and, notably, it's potent odor -- pretty much anything which dissolves in water to form a strong acid is going to have a very strong, unpleasant smell and "nosefeel" and this is already quite noticeable with benzyl chloride for example.

LC50 over four hours is 57 ppm. In a 25 m^3 room that's 1.5 grams. According to this the odor threshold is less than 1 ppm, but you become desensitized over time, which is how it can become dangerous:

https://www.nap.edu/read/11170/chapter/12

pneumatician - 12-4-2017 at 17:43

making nitric acid old school :)

https://www.youtube.com/watch?v=Lf93Jk67iFQ

jump to 32':44"