Drunkguy
Hazard to Others
Posts: 172
Registered: 23-12-2005
Member Is Offline
Mood: somewhat pissed.
|
|
KNO3 + H2SO4 -> HNO3 + KHSO4
In Wiki the following is quoted:
| Quote: |
Nitric acid can be made from Copper(II) nitrate or by reacting approximately equal weights of potassium nitrate (KNO3) with 96% sulfuric acid (H2SO4),
and distilling this mixture at nitric acid's boiling point of 83 °C until only a white crystalline mass, potassium hydrogen sulfate (KHSO4), remains
in the reaction vessel. The obtained red fuming nitric acid may be converted to the white nitric acid. Note that in a laboratory setting, it is
necessary to use all-glass equipment, ideally a one-piece retort, because anhydrous nitric acid attacks cork, rubber, and skin, and leaks can be
extremely dangerous. |
Has anybody got experience with this. I'll be checking what Bromic said about it also. Needless to say this would be attempted outside, but removing
the NOx from the fuming red liquid may not be possible since a water aspirator is not on hand and it sounds like it is some posioness nasty stuff that
would damage a mechanically driven diaphragm pump.
|
|
|
YT2095
International Hazard
Posts: 1091
Registered: 31-5-2003
Location: Just left of Europe and down a bit.
Member Is Offline
Mood: within Nominal Parameters
|
|
IIRC, Urea (carbonylamide) can be added to this red acid to convert it to white.
\"In a world full of wonders mankind has managed to invent boredom\" - Death
Twinkies don\'t have a shelf life. They have a half-life! -Caine (a friend of mine)
|
|
|
solo
International Hazard
Posts: 3967
Registered: 9-12-2002
Location: Estados Unidos de La Republica Mexicana
Member Is Offline
Mood: ....getting old and drowning in a sea of knowledge
|
|
You might gain some insight by reading this thread and its links...............solo
https://sciencemadness.org/talk/viewthread.php?tid=1851#pid6...
It's better to die on your feet, than live on your knees....Emiliano Zapata.
|
|
|
Drunkguy
Hazard to Others
Posts: 172
Registered: 23-12-2005
Member Is Offline
Mood: somewhat pissed.
|
|
| Quote: | Originally posted by YT2095
IIRC, Urea (carbonylamide) can be added to this red acid to convert it to white. |
This might be handy. How does this work exactly on a chemical level?
|
|
|
YT2095
International Hazard
Posts: 1091
Registered: 31-5-2003
Location: Just left of Europe and down a bit.
Member Is Offline
Mood: within Nominal Parameters
|
|
I don`t know, I`m only a Hobby chemist, I just know it`s used and it apparently works by removing the NOx gasses that create that red color.
sorry!
\"In a world full of wonders mankind has managed to invent boredom\" - Death
Twinkies don\'t have a shelf life. They have a half-life! -Caine (a friend of mine)
|
|
|
woelen
Super Administrator
Posts: 7977
Registered: 20-8-2005
Location: Netherlands
Member Is Offline
Mood: interested
|
|
The NOx and urea react to form H2O, CO2 and N2. It is important though that a precise amount of urea is added. Too little and dissolved NOx remains,
too much and you are making urea nitrate. It is, however, easy to do so, because the end point of adding can be clearly seen (acid becomes colorless).
|
|
|
ordenblitz
Hazard to Others
Posts: 259
Registered: 18-7-2004
Location: Northwest
Member Is Offline
Mood: Bohr'd
|
|
It’s easy to add too much urea before the color dissipates. I have had this experience before. As the COPAE says: warming and bubbling nitrogen
through while adding small amounts of urea is advisable.
|
|
|
Magpie
lab constructor
Posts: 5939
Registered: 1-11-2003
Location: USA
Member Is Offline
Mood: Chemistry: the subtle science.
|
|
I don't have a vacuum pump. But when I was researching them I noted that some have wetted parts of Teflon or other material that may be OK for nitric
acid vapor use.
Also a cold trap or chemical trap ahead of the pump might protect vulnerable pump internals. These would also trap the noxious vapors instead of
exhausting them to the atmosphere.
The single most important condition for a successful synthesis is good mixing - Nicodem
|
|
|
not_important
International Hazard
Posts: 3873
Registered: 21-7-2006
Member Is Offline
Mood: No Mood
|
|
| Quote: | Originally posted by Magpie
I don't have a vacuum pump. But when I was researching them I noted that some have wetted parts of Teflon or other material that may be OK for nitric
acid vapor use.
Also a cold trap or chemical trap ahead of the pump might protect vulnerable pump internals. These would also trap the noxious vapors instead of
exhausting them to the atmosphere. |
Better to use absorption traps - wash bottles with a solution of Na2CO3 or fairly dilute NaOH , or even urea. Still not the best thing to do.
When you're not actually trying to vacuum distill or such, but just want to draw gas through someting, the old tradition way was to have a large jug
or small barrel with a connection for tubing at the top (1-hole stopper in jug mouth) and a tap at the bottom. Fill it with water, connect tubing to
whatever needs gas drawn through it, open tap at bottom and as the water drains out it draws gases through the tubing.
Don't need N2 for bubbling through the HNO3. CO2 will work, or even clean air should be OK - pass it through several washbottles - 1st with Na2CO3 or
NaOH solution to grab any HCl or similar in the air, 2nd with 5% H2SO4 or Na/K HSO4 to pick up any ammonia; this also removes dust but still start out
with a cotton plug or some other dust filter at the air intake.
|
|
|
Drunkguy
Hazard to Others
Posts: 172
Registered: 23-12-2005
Member Is Offline
Mood: somewhat pissed.
|
|
Swim only wants the azeotrope so he'll not be needing to use vacuum. Since this distills at 120C presumably the end point wont be too hard to
determine. Also what is the the contaminent that calls for a redistillation? Is it too make the acid more concentrated or is there a hidden reason?
What ratios should be employed? Is a 1:1:1 weight all right or is there an optimized quantity that should be employed in this reaction?
He'll use an ice bath upon carefully adding the KNO3 to the H2SO4 followed by H2O dilution, since this is known to be exothermic.
|
|
|
not_important
International Hazard
Posts: 3873
Registered: 21-7-2006
Member Is Offline
Mood: No Mood
|
|
Swimming while attempting this method is a bad idea; all the reactants and products are water soluble, and allowing cool water to touch the hot
distillation vessel is not a good idea.
Instead I suggest that _you_ read the comments more carefully. There is no redistallation, just a removal of NOx from the nitric acid that includes
bubbling gas through it. The only reasons to redistill is
A) to obtain constant boiling acid, the concentration of which can be calculated using the observed boiling point and reference tables.
B) You were sloppy during the original distallation and had some of the reaction mix splat over into the product.
C) if you used urea to remove NOx and added it in excess, leaving some urea nitrate in the acid. If that happened and the urea nitrate was a problem
for the uses of the acid, you would either need to vac distill the acid away or generate enough NOx to destroy the excess urea - possibly overshooting
in that direction. If you use some urea to remove most of the NOx, so that the acid is a fairly pale yellow and then bubbling/pulling air/CO2?N2
through the acid to remove the rest.
Reduced pressure distallation is used during heating of H2SO4 + KNO# to reduce the decomposition of the nitric acid formed. This is more important on
a large scale than when making a 100 ml for hobby use. Some claim that vac distilling allows the reaction H2SO4 + 2 KNO3 => K2SO4 + 2 HNO3 to
happen, I have not seen experimental evidence of that.
Note that light will cause the constant boiling acid to slowly break down, generating some NOx.
1:1:1 ? Of what, H2SO4 : KNO3 : H2O ? Slight mole excess of H2SO4, enough water to equal about half the amount of HNO3 produced. Can't tell you
volume of H2SO without knowing what strength of acid you have, likewise the amount of water to include depends on the H2SO4 concentration. But it's
simple maths to calculate, once you know the sulfuric acid concentration. Given that MW H2SO4 is 98, KNO3 is 101, 1:1 is roughly equal mole amounts.
But an equal weight of water is way overkill, you'll be distilling off a lot of water before the acid starts to come over.
As it would be sad, and make us feel guilty, if you or SWIY were to be converted into hissing, oozing, slimely piles of acidified and oxidised
protoplasm through a miscommunication between you and SWIY, it would be a good idea for SWIY to get their own account and communicate directly.
Otherwise drop the nonsense, playing silly games with 'SWIM' and 'draming' isn't going to save your arse if the Law tumbles to you - they just do a
global replace of 'SWIM' with 'I', as SWIM stands for "Someone Who Is Me", label you a major drug dealer or terrorist because you attempted to hide,
and lock you away for a half century or longer.
|
|
|
YT2095
International Hazard
Posts: 1091
Registered: 31-5-2003
Location: Just left of Europe and down a bit.
Member Is Offline
Mood: within Nominal Parameters
|
|
does anyone know if Oxalic acid would work in place of urea instead?
I know it`s breakdown product is CO2, in fact it`s used in Hydroponics for some CO2 generators.
might it work as an alternative to urea?
\"In a world full of wonders mankind has managed to invent boredom\" - Death
Twinkies don\'t have a shelf life. They have a half-life! -Caine (a friend of mine)
|
|
|
woelen
Super Administrator
Posts: 7977
Registered: 20-8-2005
Location: Netherlands
Member Is Offline
Mood: interested
|
|
Oxalic acid does not work. It also is oxidized by HNO3 itself, giving more NO2. The good thing of urea is that it is selective. It reduced NO2, while
leaving the HNO3 untouched. Oxalic acid reduces all of it, or it does not reduce at all (when things are cold).
|
|
|
Drunkguy
Hazard to Others
Posts: 172
Registered: 23-12-2005
Member Is Offline
Mood: somewhat pissed.
|
|
| Quote: | | Dilute nitric acid may be concentrated by distillation up to 68% acid, which is an azeotropic mixture with 32% water. |
So if one has dilute nitric acid, although the bp of pure nitric acid = 83C, the water will distill first, since the azeotrope doesnt distill until a
temperature of 120C is reached.
So in a sense, if all one wanted to do is concentrate dil. HNO3, all they are doing is boiling off excess water and the nitric acid is not actually
distilled at all?
http://www.chemguide.co.uk/physical/phaseeqia/nonideal.html
Edit: I found an interesting link in another thread.
100g KNO3 has a molecular weight of 101 = 0.99 mol
0.99mol x 63.01 = 62.3g HNO3 made upon reaction with H2SO4.
Thus ~38mL H2O should be adequate for distillation to get the azeotrope?
[Edited on 11-10-2006 by Drunkguy]
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
