madscientist
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Anhydrous ammonia preparation
I have considered various possibilities for preparing anhydrous ammonia. Here are the best ideas:
2Al + 6NH4Cl --> 2AlCl3 + 3H2 + 6NH3
HSO3NH2 --> SO3 + NH3
The SO3 is easily condensed.
2NaOH + (NH4)2SO4 --> Na2SO4*2H2O + 2NH3
I weep at the sight of flaming acetic anhydride.
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Rhadon
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| Quote: | | 2NaOH + (NH4)2SO4 --> Na2SO4*2H2O + 2NH3 |
You can do this with any ammonium salt (as far as I know).
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madscientist
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The reason for using the sulfate is the fact that sodium sulfate is a dessicant. 
I weep at the sight of flaming acetic anhydride.
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Rhadon
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<*lightbulb turns on*>
Okay, now I understand. I didn't take this into account.
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rikkitikkitavi
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classical method of making NH3
2NH4Cl + Ca(OH)2 = > CaCl2 + 2 NH3
when gently heated in a flask. NH4Cl is volatile enough to be reactive with
Ca(OH)2
Usually listed in old chemistry book as a source of NH3 in the lab
If you use dry chemicals (add some CaO too the reaction (CaO+ H2O => Ca(OH)2)
you dont need a dessicant.
Can also try (NH4)2SO4 => NH4HSO4 + NH3 (@ 150 C)
/rickard
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PHILOU Zrealone
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Any soluble ammonium salt will do the job!
NH4(+) + OH(-) --> NH3(g) + H2O
If you have a high concentration of base; and a little heat the reverse equilibrium will be favourised:
NH4OH --> NH3(g) + H2O(l)
Mixing dry NH4NO3 and NaOH even when cold will make you cry like a damned for hours!Please make this outside and in tiny amounts!
The most concentrated NH4OH solution contains 35% by weight NH3; this means 350g NH3 for 650g H2O or 20,588 mole/kg!The presence of NaOH and NH4NO3
will strongly reduce NH3 solubility due to common ion effect and due to the Henry's laws of dissolved gases in liquids!!!
Pure 100% NH4OH would be 28,57 mole NH3!
PH Z (PHILOU Zrealone)
"Physic is all what never works; Chemistry is all what stinks and explodes!"-"Life that deadly disease, sexually transmitted."(W.Allen)
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PHILOU Zrealone
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NH2-SO2-OH -heat-> NH2-SO2-NH2 + H2O
NH2-SO2-OH + H2O -H(+)-> NH4O-SO2-OH
are side reactions of NH3 and SO3 formation!
PH Z (PHILOU Zrealone)
"Physic is all what never works; Chemistry is all what stinks and explodes!"-"Life that deadly disease, sexually transmitted."(W.Allen)
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Theoretic
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How about THIS?
CO(NH2)2+Ca(OH)2=>CaCO3+2NH3
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Nevermore
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| Quote: | Originally posted by PHILOU Zrealone
Any soluble ammonium salt will do the job!
NH4(+) + OH(-) --> NH3(g) + H2O
If you have a high concentration of base; and a little heat the reverse equilibrium will be favourised:
NH4OH --> NH3(g) + H2O(l)
Mixing dry NH4NO3 and NaOH even when cold will make you cry like a damned for hours!Please make this outside and in tiny amounts!
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I tried this method but in strong water solution, i agree that the ammonia released is quite alot, so much that when i added the ammonium nitrate to
the NaOH solution the solution started to fizz vigorously like when adding sodium carbonate to acids. the water keeps lots of ammonia since i ccould
still smell it after a week or more, and mixing the water with a rod would make more ammonia to be released. I think the best way would be do it with
the smallest water possible, and finely powdered reagents, so making a thick paste..
should release lots of ammonia!
Nevermore!
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Organikum
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practical
Ammonia water, the higher the concentration the better, minimum 10% and lots of NaOH (waterfree).
The NH4OH is slowly dropped from a pressure-equalized addition funnel onto the NaOH in a cooled reaction vessel, the evolving NH3 is dried by a drying
tube containing KOH and CaO, the resulting NH3 is dry enough for all to me known purposes. The KOH in the drying tube can be substituted by NaOH.
MgSO4 and CaCl are not usable as drying agents. (this applies also for methylamine which also can be prepared in its anhydrous form this way).
Important is to drop the NH4OH on the NaOH and to cool the reaction if anhydrous ammonia is deserved.
Regarding theoretical or even practical advantages of other ways, this was found to be the most usable way to do this whereby also the availability
and price of the involved compounds was taken in consideration. So it may be best for most but not for everyone, thats understood. It is also a
standard laboratory procedure - can´t be so bad I believe. Advantages are: Availability and price of compounds, controllability and thus resulting in
a quite safe reaction. 
equalized addition funnel:
not hard to improvise btw.
[Edited on 25-7-2003 by Organikum]
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frogfot
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My old chem book said to use NH4Cl and conc KOH solution. Like PHILOU said, in big concentrations of OH- equilibrium of NH4OH<==>NH3 + H2O is
strongly pushed to right. Therefore it's ok to have aqueous KOH. Now, NaOH have lower solubility but I think it could be used instead..
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Organikum
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if you want it anhydrous, better make a saturated NH4Cl solution and drop this on excess NaOH. KOH is always better but harder to get and more
expensive.
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KABOOOM(pyrojustforfun)
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what about dry ammonia generating compositions!
eg: burn Mg ribon in O2/CO2 free air. collect Mg3N2 ashes. mix each mol with 3 mol finaly powdered (NH4)2SO4. I expect when the mix is heated this
reaction happen:
Mg3N2 + 3(NH4)2SO4 => 3MgSO4 + 8NH3
the reaction is of course exothermic but don't know if it generates enough heat to make it selfsustaining(it'll be deflegration if so!).
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Quieraña
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My favorite way as of lately is any ammonium salt, preferably nitrate bc easiest for me to find here and barium hydroxide. Most hydroxides i knew in
the past get real hot when made aqueous, but not barium. Barium OH and ammonium nitrate, combined dry, begins production and within a minute frost is
on the beaker of mixed salts and a mean temperature around minus 25C can be found. The anhydrous is barely boiling , especially if there is a lif
placed on. Requires not even an atmosphere of pressure to keep indefinitely.
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clearly_not_atara
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^these kinds of practical tricks are what makes SM great! Nice work!
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