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H2SO4+KNO3=HNO3

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john bunsenburner

Tue Feb 17 2009, 03:51PM

Registered Member #1937 Joined: Sun Jan 25 2009, 12:28PM
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Posts: 53

Well i want to make my self a batch of highly concentrated nitric acid, and while many use 90-98% sulfuric acid to make nitric acid from KNO3 i was wondering weather or not i could use some weaker acid to? Do you have any other advice for me when doing this, and yes i will work out doors...Thank you.

Shaun

Tue Feb 17 2009, 05:26PM

Registered Member #690 Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616

You can use weaker reactants, but you will get proportionally weaker products. If you want fuming nitric, you will have to go all out and use the concentrated sulfuric, or find a way to distill the weak HNO3, which is no easy task either.

john bunsenburner

Wed Feb 18 2009, 09:24AM

Registered Member #1937 Joined: Sun Jan 25 2009, 12:28PM
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Could i distil the sulfuric acid? I think i might get my hands on some 30-40% but no more...
or i could make sulfuric acid...would that be worth it?

Shaun

Wed Feb 18 2009, 04:16PM

Registered Member #690 Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616

Getting 30-40% sulfuric acid to 98% or so is very difficult for an amateur. I you are outdoors and behind a shield, you could heat it strongly (with boiling chips). This would increase it a good amount I think, but just how much I'm not sure.

Really it would be easier to just search harder for some concentrated stuff; there's nowhere near as many restrictions on it as nitric acid. I bet you could buy it online if you looked in the right places.

john bunsenburner

Wed Feb 18 2009, 06:44PM

Registered Member #1937 Joined: Sun Jan 25 2009, 12:28PM
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I rather not buy things online, its horrible to ship to switzerland, making H2SO4 is very difficult and so thats out of the question. I think I will just search harder. If something required very concentrated acid do you think it might also be worth a shot with less conc acids(experiment requires very high conc nitic acid could i use lower concs as well)? And if I manage to buy some strongly diluted HNO3 would distilling it be worth the trouble or should i try makign it instead? And does only H2SO4 work for producing HNO3 or culd another acid work too?

Backyard Skunkworks

Wed Feb 18 2009, 07:16PM

Registered Member #1262 Joined: Fri Jan 25 2008, 05:22AM
Location: Maryland, USA
Posts: 451

It would help a bit if you told us what this experiment is.

Remember that if it involves illegal quantities of explosives, 4HV is not the place to discuss it.

Billybobjoe

Wed Feb 18 2009, 08:05PM

Registered Member #396 Joined: Wed Apr 19 2006, 12:55AM
Location: Pittsburgh, PA
Posts: 176

Shaun wrote ...

Getting 30-40% sulfuric acid to 98% or so is very difficult for an amateur. I you are outdoors and behind a shield, you could heat it strongly (with boiling chips).

It's about a thousand times easier for an amateur to boil down sulfuric acid (95-98%) than to distill nitric.

Chris

Wed Feb 18 2009, 10:52PM

Registered Member #8 Joined: Thu Feb 02 2006, 04:34AM
Location: Harlowton, MT, United States
Posts: 214

You pretty much need concentrated H2SO4 to distill dilute nitric acid past the azeotrope anyway, so you might as well just use it to produce the concentrated nitric directly; you'll need it either way. It is available around here as drain cleaner; not very pure, but perfectly effective at making nitric acid.

As for concentration of dilute sulfuric, in my opinion it is easier, or at least arguably safer, for an amateur to pyrolyze dry CuSO4 (made by adding dilute sulfuric to copper oxide or other copper salts, then reusing the CuO that is left after the process to do it again) to SO3 and then make concentrated H2SO4 from that than it is to simply distill sulfuric acid to high concentration. This is especially true if you want very high purity, like reagent grade, and want to do it efficiently (as opposed to just boiling down H2SO4 in the open with no reflux column). This is because concentrated sulfuric has a boiling point that is really pushing the limits for glass distillation apparatus, about 330Â°C, and you'd be at quite a risk of breakage due to thermal shock. It is hard to imagine how much such a breakage would suck. It cannot be done in steel or other metal apparatus since the wet acid would attack it aggressively. Doing it in an open vessel would lose a lot of acid. On the other hand, decomposing dry CuSO4 to CuO + SO3 requires higher temperature, about 650Â°C, but can be done easily in a steel retort since the anhydrous material is not corrosive to steel or most common metals. The raw SO3 is then very easy to distill to high purity in glassware as it is quite volatile, boiling at 45Â°C. The downside is that SO3 is somewhat more dangerous to work with than H2SO4; it is a much stronger dessicant, reacting violently with water, and quite volatile as I mentioned. H2SO4 is prepared from SO3 only by adding SO3 to a smaller amount of strong H2SO4 to form intermediates called oleum, which is then added in turn to more water; the single step reaction SO3 + H2O --> H2SO4 is much too violent and will result in acid steam. With this process however, you could make 100.0% anhydrous H2SO4, which in reality contains the equilibrium 2H2SO4 <--> H3SO4+ + HSO4âˆ’, and you can even make solutions which from a stochiometry standpoint contain more than 100% H2SO4.

The other downside is this is a multi-step process which takes a long time compared to simply distilling dilute H2SO4. However, if you have the steel retort already capable of doing the pyrolysis, then you will also be able to recover 50% of your sulfuric acid from the nitric acid process by the reactions 2NaHSO4 -(315Â°C)-> Na2S2O7 + H2O and Na2S2O7 -(460Â°C)-> Na2SO4 + SO3. The recovery of the remainder of the acid from Na2SO4 though is more involved and almost certainly not worth your effort. I suppose you could do it with an electrolytic membrane or amalgam cell though if you were really hard up for H2SO4, but that would be a dilute process so probably not worth it. If you had such a cell you could just make your nitric acid directly from KNO3 anyway but you'd still need concentrated sulfuric to concentrate it.

john bunsenburner

Thu Feb 19 2009, 09:32AM

Registered Member #1937 Joined: Sun Jan 25 2009, 12:28PM
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Posts: 53

Thanks for the responses, especially yours chris as it was very informative and helped alot. As I asked before, besides yields does the concentration of nitric acid make a difference in the results you get or not? And as I noticed that making H2SO4 is extremly complicated and also that distilling it isnt very easy I think it would be best if I just looked around for concentrated acid, or forgot about the whole thing. I read a recipy were a guy simply poured KNO3 into H2SO4 and said it would be good enoth for producing several chemicals(and explosives) which require HNO3. Do you think he is talking shit or would this work as I really do not need very large amounts of high purity, but just a little HNO3 for a few grams of several chemicals(which also dont really have to be all that pure as I wil use them quickly and not store them and s it doesnt matter how stable they are).

asimov13647

Sat Apr 04 2009, 02:16PM

Registered Member #2048 Joined: Wed Mar 25 2009, 08:58PM
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Even after you disolve KNO3 in H2SO4, you will need to distill the mixture to produce HNO3. There is a scene in Jules Verne's 'The Mysterious Island' in which the castaways manufacture sulphuric and nitric acids from materials on hand. But if you are going to make fuming nitric acid you will at least need a retort. Sulphuric acid, the precursor of nitric acid, can be concentrated simply by boiling the water out of it.

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