localbroadcast
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Danger of adding water to NH3 + lithium solution
Hello.
I was reading a reaction that uses anhydrous ammonia and lithium to produce free electrons (birch reduction)
After the main reaction takes place, it says to allow most of the ammonia to evaporate off, then to dilute the rest of the ammonia with water. This
is a pretty scary thought to me, given that there is still quite possibly lithium still dissolved in the ammonia.
Is there any danger at this point of the lithium reacting with the addition of water?? Lithium would normally react with water violently if it wasn't
in the ammonia... So does the fact that it is dissolved in the ammonia make it no longer reactive with water in the same way?
Thanks
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DraconicAcid
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Lithium doesn't react very violently with water- it's a gentle fizz rather than the hiss and bang you get with large pieces of sodium. I'd just add
the water slowly.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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aga
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Quote: Originally posted by localbroadcast  | This is a pretty scary thought to me, given that there is still quite possibly lithium still dissolved in the ammonia.
Is there any danger ... |
Yes, there is always Danger, no matter what you do.
Sit at home and watch TV : a plane or meteor or part of a satellite might crash onto your house and kill you.
Add water to a solution of chemicals, well, it might explode, but at least you can control the quantity of each thing, and prepare with adequate PPE
for that eventuality.
So just think of what could happen, be prepared, and then try it.
There's nothing to say that you won't get killed during the experiment by a stray bullet from a psycho on a rampage, but at least you can minimise the
dangers from the Known risks.
Do a risk assessment (i.e. think about it for at least 5 mins) take appropriate care, do the experiment, see what happens.
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Loptr
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It's going to be exothermic, but a lot of reactions are exothermic.
Just make sure you aren't doing this in a bucket.
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byko3y
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Just forget about alkali in liquid ammonia, pretend the reaction is non-existent and nobody have ever been able to perform it.
Why? Because ammonia is flamable and toxic by itself, and after you added a reactive metal to it - it's a recipe for a disaster. And in case you
somehow managed to survive this - you will have a hard time explaining to cops, which were called by neighbours, what you are doing with all this
stuff.
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macckone
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Ignoring byko3y ammonia is a cryogenic liquid that vaporizes and is fairly harmful to your lungs. It is unlikely to catch fire. However, he is
correct in that the primary use of this reaction in a residential setting is the manufacture of illegal substances. And just having liquid ammonia
and lithium is sufficient to get you arrested as a manufacturer of illicit substances in the land of the free.
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localbroadcast
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I was in no way ever considering actually doing the reaction.. I'm more of an armchair chemist.. I like to read about the stuff because it's
interesting to me for some odd reason..
So as long as the addition of water is at a slow pace and the cooling of the vessel is maintained then there should be no large crack bang boom vavoom
poof of smoke and shreeks of death? Good to know!
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byko3y
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About water and ammonia interaction https://www.youtube.com/watch?v=vgBe0fsPcjk
How the ammonia burns https://www.youtube.com/watch?v=n4ktAaGAyLc and this is how it explodes https://www.youtube.com/watch?v=MMtv9kWAoTs (why it happened https://www.youtube.com/watch?v=2ESemJo0XcI )
Storing liquid ammonia is pretty much the same as storing liquid propane.
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Scr0t
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Alternatively you could use ethylenediamine or some other less volatile amine as it's safer than using liquid NH3
See woelens post...
https://www.sciencemadness.org/whisper/viewthread.php?tid=32...
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Dr.Bob
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Depending on how the reaction is done (concentration, time, temp, and Fe catalyst), I believe that you can eventually convert the Li(0) and NH3 into
LiNH2 (lithium amide) with the evolution of H2, and that is much less reactive than lithium with water, making LiOH and NH3 when reacted with water.
I have not done that myself, but did see a Birch done years ago, and it was quite pretty.
It is not a simple reaction to do properly, due to the need for anhydrous ammonia, dry ice, lithium, and the proper glassware, but it can't be too
difficult if people are doing in Walmart's bathroom. I doubt that many of them do it well or safely, however. The evolution of H2 is much more
likely for the explosion potential than the ammonia itself, but the ammonia is flammable itself as well. I try to stick to simple reactions like
those in hot sulfuric acid and a reaction involving two different diazo compounds (someone asked me about running that one, and even I was not willing
to volunteer).
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Templar
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lol get a load of this guy, as dangerous as propane... I dont think so tim
I cant immediately find the activation energy or actually much data about it burning in air. The only disaster I could find out about was where a fire
started next to a large ammonia tank, caused it to fail and leak large amounts of ammonia gas. It is flammable, but it must be sustained by another
source of heat to continue combustion as it seems its autoignition temperature is below that of the ammonia combustion itself. Keep it away from
platinum metal, high temperature sources or flames.
Lets not get scared here.
But if anyone is dealing with liquid ammonia, keep in mind the enthalpy of mixing and how it hydrolyzes, keep it away from water. The big hazard would
be the ammonia gas; Ive had a wee cloud of that form once and it blinds/chokes you temporarily. Make sure you deal with it in a fume hood or outside.
The Li metal reacts to form LiN3 I think? Hydrogen gas is a hazard if the Li gets in contact with water. Pressure and flammability.
He who fights with monsters should be careful lest he thereby become a monster. And if thou gaze long into an abyss, the abyss will also gaze into
thee.
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Darkstar
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| Quote: Originally posted by localbroadcast |
So as long as the addition of water is at a slow pace and the cooling of the vessel is maintained then there should be no large crack bang boom vavoom
poof of smoke and shreeks of death? Good to know! |
The only time I'd be all that concerned is in the event that something flammable was used as a co-solvent or proton donor. A little ammonia may not
catch fire that easily, but a flask full of THF or EtOH might. Besides, if it bothers you that much, you could always just toss in some
NH4Cl to quench the reaction and scavenge any remaining electrons before boiling off the ammonia.
| Quote: Originally posted by DraconicAcid | | Lithium doesn't react very violently with water- it's a gentle fizz rather than the hiss and bang you get with large pieces of sodium.
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Poor lithium. It's such a shame, too. It has the lowest reduction potential and the highest hydration energy of any alkali metal, yet its reaction
with water turns out to be the most pathetic of them all. If only its melting point weren't so much higher...
Molten lithium is freaking insane!
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blargish
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If the goal is to quench the reaction vessel, I guess you could alternatively slowly add isopropanol to to mixture to react with the lithium to make
lithium isopropoxide (I have seen this method used when sodium is solvated in liquid ammonia, as a means of safely neutralizing the final contents of
the vessel).
Still, the use of water should not be a big deal at all due to reasons stated above by others.
BLaRgISH
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Corrosive Joeseph
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Apparently dropping a few ice cubes in slowly, one by one, does the trick.....................
Being well adjusted to a sick society is no measure of one's mental health
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Eskarari
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Use a trigger sprayer with h20 in it and half a teaspoon of naOh to help seperate the h20/base layer with the ammonium chloride impurities and
lithium hydroxides . This will also help the solutions seperate
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hyfalcon
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You obviously don't know the first thing about proper nomenclature. It's not h2O, it's H2O or H2O.
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woelen
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Eskarari is the guy with several PhD's in chemistry and related subjects . . . 
(for more info: see detritus)
But now let's become serious: By this I give a warning to you (Eskarari). Be precise in what you post, use proper symbols (Capital letters and small
letters in formulas) and stop posting crap. I do not want anymore to see any other member of sciencemadness have a valid reason to report your posts!
[Edited on 25-6-15 by woelen]
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