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Author: Subject: Nitric Acid, specific questions from a newbie
binaryclock
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[*] posted on 18-5-2013 at 21:23
Nitric Acid, specific questions from a newbie


I have successfully distilled HNO3 from KNO3 + H2SO4 using fractional distillation. My yield was lower than expected, but the purity was very high as it fumes violently in air.

A few questions if you don't mind:

1. When you see puffs of white smoke from removing the glass stopper or from the vent/vacuum outlet during distillation, about how many PPM are those fumes? I'm always wearing a proper 3M carbon respirator so I'm playing it very safe.

2. How much nitric acid is theoretically typical to distill from 50g of KNO3 and 55g of H2SO4? I didn't get much, but this was a test run and I know the mistakes I made. Too much heat at points, too little at others.

3. What is the best way to store this nitric I have created? Right now I have it in the collection vessel with a glass stopper on the top. From what I'm read, an all glass container is the only way to store it? Should I be freezing this or store at room temperature?

4. Before any H2NO3 condensed in the condenser, I saw a brown gas move all the way to the collection flask. I'm assuming this is nitric oxide. Shouldn't this gas of at least condensed through the long condenser I have? How did it make it through to the collection flask? 3-4 minutes later the nitric acid condensed just fine, but I'm still trying to understand how the first brown gas made it through without turning in to a liquid.

Thanks!

[Edited on 19-5-2013 by binaryclock]




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[*] posted on 19-5-2013 at 02:55


1) No Idea, but I dont wear a respirator and the fumes can be pretty biting if you dont open the container outside.

2)
the reaction goes: H2S04 + 2KNO3 -> 2HNO3 + K2S04
you used 55g sulfuric, which is 0.561moles
50g KNO3 is 0.495 moles
This means you used roughly 2x the amount of sulfuric you needed (2:1 ratio)
so based off KNO3, the theoretical yeild would also be 0.495 moles, or 31.68g)
Check my stoichiometry for me will you? I kinda rushed that so there could be something wrong.

3) I store mine in an amber glass bottle with PTFE tape wrapped around the thread. The lid is made from a white plastic, I dont know what kind.
Not PVC though, thats for sure. Its held up fine over the last 2 months. plastic has got a little yellow though.

4) mate, its called a gas for a reason. Its a gas. IT isnt going to condense unless your running something wayyy below zero through your condenser. The NO2 will dissolve in water to make HNO3, but there shouldn't be any water in your reaction anyway. Which leads to the question, why fractional distillation?? your distillling one liquid here.




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[*] posted on 19-5-2013 at 03:29


For stochiometry I think it's safer to suppose that KHSO4 will form and anyway an excess acid is a good idea (unless it has a lot of extra water in it).
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[*] posted on 19-5-2013 at 05:56


For easier storage, distill at, or dilute to %70. This is usfull for mast reactions, and if RFNA is needed, just redistill some of it with a little H2SO4.

I am not sure on PPM, but if you can smell it (kinda a bleachy smell) then your fumehood isnt doing the trick. Avoid inhaling the fumes as much as possible. They will make you feel, not so good.




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binaryclock
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[*] posted on 19-5-2013 at 20:52


Thanks for all your suggestions. I thought the ratios for correct stoichiometry was 1:1? How did you determine that I used twice the amount required?

I'm a newbie here so my question is purely a newbie question and not challenging you. I want to learn!





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[*] posted on 19-5-2013 at 23:39


papaya given that you can make HN03 from NaHS04 I think that you will form K2S04, or though it is possible there maye be some kind of equilibrium going on between KHS04 and K2S04. If thats the case, then you may want to have excess of KN03 or H2S04 depending on which reagent is the hardest/most expensive to get.
In any case, I agree that it is good to have an excess of sulfuric, for two reasons. Firstly, to remove any water that may be present. Secondly, because the stoichometric mixture does not become a liquid until like midway through the distillation. Until then, its a slurry of KNO3 and H2SO4 which promotes the formation of NO2 gas for some reason.

But @binary I really suggest you learn basic stoichometry. I myself am only in my second year of chemistry at school and I learnt this kind of thing a year ago. Its pretty basic stuff thats easy to learn and really helpful.
Ill explain my reasoning in more detail but you might not understand the terms I use:

The reaction as stated before is: H2S04 + 2KNO3 -> 2HNO3 + K2S04.
The important thing here is that 2 molecules of KNO3 react with one molecule of H2SO4 (so a ratio of 2:1). This does NOT mean you can react them in a ratio of 2:1 by weight (although in this example the correct ratio is almost 2:1 by weight, so its a bad example:mad: ).
Now the molecular weight of KNO3 is 39.1+14.01+16x3, which is 101.11. 2x this is 202.22, needed later on
the molecular weight of H2SO4 is 2+ 32.07+16x4 which is 98.07
So remembering they react in a ratio of 2:1 by moles, they react in a ratio of 202.22:98.07 by weight. Note that this is almost exactly 2:1 by weight as well, but this is not always the case by any means.

Hope this helps!

[Edited on 20-5-2013 by Oscilllator]




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[*] posted on 20-5-2013 at 19:17


Thanks a ton! I do know basic stoichometry, but I forgot to balance the reaction. Therefore it takes 2 KNO3 to react with one molecule of H2SO4! This is where I got confused so thanks for writing it all out it really helps to understand the entire process.

Ok next question. After my distillation is complete, I am left with a salt cake in the reaction flask. When I remove the glass stopper it fumes indicating there is still nitric acid still in the reaction flask. What would be the best way to clean this flask without spraying fumes everywhere when I add water? Of course I'll be using heavy gloves and a respirator, but I'd rather not spread fumes in my cleaning room as well. I guess now that it's summer I could take it outside to the road and wash it out there with the hose, but if it wasn't summer what would be the safest way to accomplish the cleaning of the reaction flask?

Thanks,

bc


[Edited on 21-5-2013 by binaryclock]




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[*] posted on 20-5-2013 at 19:32


Quote: Originally posted by binaryclock  

Ok next question. After my distillation is complete, I am left with a salt cake in the reaction flask. When I remove the glass stopper it fumes indicating there is still nitric acid still in the reaction flask. What would be the best way to clean this flask without spraying fumes everywhere when I add water?.....

[Edited on 21-5-2013 by binaryclock]


I guess one way would be to use a pressure equalizing addition funnel but why bother? Just take it outside and add your water. It doesn't matter if it is summer or winter.

There is a picture here
http://en.wikipedia.org/wiki/Dropping_funnel

[Edited on 21-5-2013 by vmelkon]
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[*] posted on 20-5-2013 at 22:00


A way to clean out the acids left over assuming you don't want to keep them for any reason is to fill a bucket with water and pour the acids in. If you are especially worried about getting fumes everywhere, stopper the flask, submerge it in the bucket and then release the stopper. This should help control the release of any fumes. Remember!, never add water to acid! I made this mistake once and had a large mess on my hands afterwards.
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[*] posted on 20-5-2013 at 22:56


Both good suggestions. I do have a seporatory funnel so I could use that method and add water slowly in my garage or something.



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[*] posted on 21-5-2013 at 00:46


You should not add water slowly to the remains in your distilling flask, you'd better immerse it completely in a bucket full of cold water and allow water to flow in at once, while it is deep under water. The solid then is covered with a lot of water at once and you only get dilute stuff around the flask and hardly any fumes will make it to the surface.

Quote:
For easier storage, distill at, or dilute to %70. This is usfull for mast reactions, and if RFNA is needed, just redistill some of it with a little H2SO4.
This is a good idea. Storing fuming nitric acid is a pain in the ass and nearly every stopper is eaten by the fuming acid! Using an all glass bottle with glass stopper also is not really an option, because fumes easily get out of the bottle along the glass stopper. The only acceptable storage option for fuming nitric acid to my opinion is a glass bottle with a sturdy plastic cap, which has a teflon liner inside.

If you make 70% acid, then be very careful. Do not simply pour water into the acid, but do the opposite, pour acid in water and do this very slowly and with swirling to spread out heat evenly. Anhydrous HNO3 gives off a lot of heat when mixed with water! Also keep in mind that you should not simply take 30 ml of water for 70 ml of acid. The conc. acid has a density of a little over 1.5 gram per ml. So, in order to make 70% acid by weight, take 7 ml of water for each 10 ml of acid. Higher concentration of acid leads to storage problems and requires special teflon caps.





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[*] posted on 21-5-2013 at 00:52


I poured my K2SO4 out while it was still molten, and that got rid of most of it (pour it in drain). After it has cooled down to <100c, I filled it up with water and the warm water removed that vast majority of what was left in the flask. The flask was completely cleaned with a couple more rinses. I didn't notice any Nitric acid smell, but that doesn't mean it wasn't there. I did all this outside with no respirator and no gloves and was completely fine (gloves are overrated anyway).

In your case if the K2SO4 is in a solid mass at the bottom of the flask I would fill it with hot water (from a kettle or something) and swirl it around a bit. Sure you may get a couple of whiffs of nitric acid but nothing serious, provided you do it outside. Just keep rinsng it with hot water until all of the K2SO4 is gone.




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