Concentrating nitric acid report

[stanfield]

I bought 1 Liter of 58% nitric acid several weeks ago and today I decided to (try to) concentrate it...
(Usually, I made my nitric acid by distillation of sodium nitrate and sulfuric acid)

So, I put the entire bottle of nitric acid in the boiling flask then I added 1 Liter of 92% sulfuric acid (yes, I know this must be 2 L but I didn't have an another liter on(under?) the hand...)

Then I began the distillate but after 2 hours, I got the same nitric acid (58%)

So, I have 3 questions :
- Must I boil down the acid to 68% before ?
- When will I know that my acid is at 68% ?
- Must I only add 2 Liter of sulfuric acid ?

thanx for all !

<small>[ July 09, 2002, 02:15 PM: Message edited by: stanfield ]</small>

[DBSP]

Most likely the H2SO4 got to diluted by all the water and didn't function properly. Kepp the acid as it is and add a nother liter as soon as you get it, and then distill it. If you decide to do anything before that you are risking to loose lots of acid.

[stanfield]

ok, thanx

Theoriticaly, when you finished distilling your mixture, there's only diluted sulfuric acid who's remaining in the boiling flask ? right ? So, if you boild it down, you could recover it's original concentration, no ?

In other words : you get back you sulfuric acid and lot of concentrated nitric acid ? life is wonderful ! (chemistry too ! :) )

see ya !

<small>[ July 09, 2002, 04:37 PM: Message edited by: stanfield ]</small>

[ALENGOSVIG1]

Yes you can reuse the H2SO4 if you heat it to drive off the water content.

[stanfield]

That's what I though :)
So, I think this method is better than nitrate+sulfuric :
- lesser time
- you can get back you sulfuric acid
- I think there are less nitrogen oxides produced during the process...

What about the temperature ? I have this one (dunno how to say in english!):
<img src="http://stanfield.150m.com/tete.jpg" alt=" - " />
and not a Vigreux column :
<img src="http://stanfield.150m.com/vigreux.jpg" alt=" - " />

see ya !

EDIT : I haven't yet any vacuum pump <img border="0" title="" alt="[Frown]" src="frown.gif" />

<small>[ July 09, 2002, 05:41 PM: Message edited by: stanfield ]</small>

[Mr Cool]

If I were you I'd do it in a few smaller batches: boil down your litre of H2SO4 to get it very strong, add a few hundred mL of 58% HNO3, distil, boil down the H2SO4 again, add more HNO3, distil...

[stanfield]

Is there a way to calculate how much sulfuric acid you need ?
this method is too long, Mr cool...

[Microtek]

I use equal volumes of 62 % HNO3 and 96 % H2SO4, and it works excellently even without vacuum. You have to make sure that the temp doesn't get too high though, or the water will come over as well.

[stanfield]

you're lucky ! I use a bit less concentrated nitric acid and it didn't work ! (my sulfuric acid too was a bit less concentrated...)

[Microtek]

I think the reason is that the water was boiled off of the H2SO4. As you said yourself: Once you're done distilling, you could concentrate the sulfuric acid by boiling the water off. At lower concentrations H2SO4 will give off the water at lower temp, so if you leave the setup you need to be sure the heating isn't too much, or you'll just end up with your original nitric acid in the receiving flask.

[stanfield]

I just tested out making HNO3 by distillation of ammonium nitrate + sulfuric acid = it didn't work !

By the way, what's the equation of distillation of calcium nitrate + sulfuric acid ? I know the one which involve sodium nitrate (The one I always use) but calcium nitrate seems to be cheaper than sodium nitrate...

thanx !

[kingspaz]

H2SO4 + Ca(NO3)2.4H2O ---&gt; CuSO4.2H2O + 2HNO3 + 2H2O
i included water of crystilisation in the equation to show that water will be produced as a by product of the conversion. i think KNO3 is prefered because (as far as i know which isn't very <img border="0" title="" alt="[Wink]" src="wink.gif" /> ) it has no water of crystilisation.

[stanfield]

damn... NaNO3 too hasn't water ? (Here NaNO3 is really cheaper than KNO3 !)

[rikkitikkitavi]

NaNO3 is hygroscopic, which KNO3 isnt. However even KNO3 contains
water to some extent so for maximum yield , dry it.

I have tried distilling with CaNO3, however with negative results.

First, Ca(NO3)2 is extremely hygroscopic and is hard to dry properly.
I dried it in a oven at 150 C. Even after that one or two hours of exposure to air lead to moisture being absorbed into a sticky mess.
quick mixing after the drying, thus.

The Ca(NO3)2 sold as 15.5 % N-content is a double salt:
Ca5(NO3)10*NH4NO3*10 H2O. I separated the NH4NO3 by adding Ca(OH)2 and boiling it for several hours. (NH4 + OH =&gt; NH3 + H2O)

more important is that the reason why it failed was probably
a insoluble layer of CaSO4 formes on the surface of the Ca(NO3)2 preventing furhter reaction. Some CaSO4 dissolves in H2SO4 forming
CaHSO4 though, but not much. The reaction progresses slowly.
I could feel a clear scent of nitric acid thoug, and when heated it gave of HNO3-vapour.

( Pure sulfuric mixed with CaSO4 ,and later filtered of to a clear solution clearly preciptates CaCO3 when neutralized with Na2CO3. But not much though. Some CaSO4 goes into solution with H2SO4. A more dilute H2SO4 preciptates more CaCO3. I havent been able to collect the preciptate though, since the crystals where extremely fine and simply wouldnt settle or be filtered. )

/rickard

[ALENGOSVIG1]

I always distill my HNO3 with CaNO3. For me, CaNO3 is the cheapest and most easily availible nitrate. It is however VERY hygroscopic. Luckily the plastic buckets it comes in seals very well and the CaNO3 doesnt seem to absorb any (very little anyhow) water. But, if i leave the prills out, they will abosrb so much water it becoms liquid!

Also, i get better yeilds (after being tripple distilled with H2SO4) when using CaNO3 when compared to KN03 or NH4NO3.

[rikkitikkitavi]

Alensovig, what ratios Ca(NO3)2:H2SO4 do you use?
Do you know your temperature in the flask when the HNO3 starts to come over?

/rickard

[stanfield]

so, the calcium nitrate method work ! For me too, this is the cheapest nitrate !

Does it have an effect on nitrogen oxides formed during the reaction ? less or more ?

thanx !

[stanfield]

Wait a minute ! I made some calculation last night and I found that for 1000 mL of sulfuric acid, you get about 400 mL of nitric acid...

With sodium nitrate, I get more than 1 Liter of nitric acid !!

But this was last night and I was tired so I maybe made a fault...

[xoo1246]

Could people take pictures of their distillation setup and post them, would be interesting. If you want to, that is.
I was planning to buy a setup, but then again, I have never used one. I know how they work, what parts there are etc, but tips would be nice. What heat sources are you using, electrical, flame, oilbath, etc?
I'll soon attent a chemistry education, hopefully I'll learn something there.

[stanfield]

I taked photos of my distillation apparatus but I haven't them yet ! As soon as possible I will post them here !

I personaly use a sand bath...

[stanfield]

What a luck ! I just found a reseller near me who sell 25Kg bag of potassium nitrate for 12€ !
So, what's the equation of the distillation with potasium nitrate ?
3KNO3 + 2H2SO4 =&gt; 3 HNO3 + ... ???

thanx !

<small>[ July 22, 2002, 12:15 PM: Message edited by: stanfield ]</small>

[DBSP]

KNO3 + H2SO4 --&gt; HNO3 + KHSO4

[stanfield]

thanx,...
At this moment, I'm distilling and the distillation with potassium nitrate take more time than the one with sodium nitrate !
I used 3KNO3 + 2H2SO4 =&gt; 3 HNO3 + ... so the sulfuric acid is in little excess which I like.
I used 500 mL of sulfuric (96%) and 1400g of KNO3

I'm really pissed off ! I hope this distillation will finish before going to bed :mad: !

thanx elsewhere :)

[stanfield]

argh ! I justed finished my distillation and I ONLY GET 300 mL of NITRIC ACID !!! (theory : 587,5 mL !!!!) This method really sucks ! I really prefer sodium nitrate ! Furthermore, the nitric acid looks really red so I have to purify it with urea ! With sodium nitrate, the final nitric acid is pale yellow and no purification is needed !

shit !

<small>[ July 22, 2002, 12:53 PM: Message edited by: stanfield ]</small>

[DBSP]

Stanfield, I don't thik that your equation is right. As I posted before; KNO3 + H2SO4 --&gt; HNO3 + KHSO4, this means that:

3KNO3 + 2H2SO4 --&gt; 2HNO3 + 2KHSO4 + KNO3, which means no excess H2SO4.

What ammounts of chems did you use?

[stanfield]

I used 3KNO3 + 2H2SO4 --&gt; 2HNO3 + 2KHSO4 + KNO3
so, 500 mL of H2SO4 and 1415g of KNO3.

[mongo blongo]

I agree with stanfield that NaNO3 is the best. I have tried KNO3 and NH4NO3 with shitty yields.

EDIT-WTF? You have KNO3 on both sides of the equation? It's:
KNO3 + H2SO4 --&gt; HNO3 + KHSO4

<small>[ July 22, 2002, 10:55 PM: Message edited by: mongo blongo ]</small>

[stanfield]

I have a friend who said that the correct equation is :
2 KNO3 + H2SO4 =&gt; 2 HNO3 + K2SO4
He saw it in a chemistry book ! So this must be right ? what do you think about it ?

<small>[ July 23, 2002, 02:50 AM: Message edited by: stanfield ]</small>

[rikkitikkitavi]

this has been covered before in older topics...

first reaction
H2SO4 + KNO3 =&gt; HNO3 + KHSO4 takes place at about 100-150 C.(bp HNO3 84C) @ 1 atm.

second reaction

KHSO4 + KNO3 =&gt; K2SO4 + HNO3 takes place at much higher temperature so much of the HNO3 decomposes:

2HNO3 =&gt; H2O + 2NO2 + 1/2 O2

In the old days, NaNO3 was used, probably becaues it is much cheaper and the KNO3 was used for black powder.
(there is very little KNO3 in nature but NaNO3 exist in chile fex)

The reaction was stopped after the first reaction, and the NaHSO4 formed was sold as "niter cake" , since the yield of the second reaction was so low that it wasnt economically feasible drive it that far.

/rickard

[mongo blongo]

Yes so Stanfield , if you use your equation then you are not using enough H2SO4 and you will be wasting your KNO3 unless you heat it way over the decomposition temp of HNO3 which of course is bad. Try the other equation that takes place at the lower temps and you will see a better yield. <img border="0" title="" alt="[Wink]" src="wink.gif" />

[stanfield]

in brief : H2SO4 + KNO3 =&gt; HNO3 + KHSO4 if I understood...

[mongo blongo]

Yes, that will be the equation for distillation if you want the least amount of NOx at the normal temps used in this procedure.
Good luck dude <img border="0" title="" alt="[Wink]" src="wink.gif" />

[stanfield]

During my (wrong) distillation the temp was always between 90 and 100°C (with a sand bath), is this fine ?

thanx...

[stanfield]

Today I made a distillation with sodium nitrate :
- 500 mL of 96% sulfuric acid
- 1200g of NaNO3

I obtained 460 mL of nitric acid instead of 583 mL theoriticaly...

Since I have my 5 Liter distillation apparatus, all the nitric acid I made is really RED ! Before, with my 1 L distillation apparatus, it was yellow, I didn't have to purify it ! why ?

I think to obtain a maximal yield, I should buy a vacuum pump... Today I only tried with my mum's aspiratory during 5 min and the nitric acid really pissed !

see ya !

[woo-jong]

Does 1 mole of sulfuric acid absorbs 1 mole of water?

[mongo blongo]

I'm not sure how to work it out but it would be using "ligans" (sp?). Water ligans will be attracted around the molecule and it depends on the shape and size of the molecule. I did this a while back in chem class but I have the memory of a goldfish so I'm not sure if that is all right.

[firebreether]

woo, H2SO4 and H2O are infinitely miscible(sp).

mongo blongo - i think you mean ligands. Like [Cu(NH3)4]2+.