Sciencemadness Discussion Board - Ammonia from H2 and KNO3

Ammonia from H2 and KNO3

Random - 24-9-2010 at 01:02

I read on one site that ammonia can be made from hydrogen and KNO3. It says to use aluminium, naoh - probably for H2 production and KNO3. Nitrogen obviously is from KNO3 for ammonia, but what is the real reaction. Can I bubble H2 through KNO3 solution for the same affect? Will this reaction happen if I use ammonium nitrate:

H2(g) + NH4NO3(aq) --> NH4OH(aq) + NH3(g)?

woelen - 24-9-2010 at 01:34

Making ammonia from H2 and KNO3 in theory cannot be done. What can be done, however, is making small amounts of NH3 from KNO3, NaOH and Al.

If you make a solution of NaOH and KNO3 (or NaNO3 if you wish), and you add aluminium foil to this solution, then hydrogen is produced by means of the well known reaction of aluminium with alkaline solution. But at the surface of the reacting aluminium there will also be reduction of the nitrate ion to ammonia (so-called nascent hydrogen is formed, which either combines to form molecules of H2, or reacts as a strong reductor). Do not expect this to be a reaction which has any preparative value, the result is a nasty mess and the efficiency of the reaction is low. But if you add some aluminium foil to a solution of NaOH + KNO3 and you allow this to stand and wait till the reaction is over, then you can smell the ammonia from the reaction.

Bubbling H2 through a solution of KNO3 does not give any reaction. The gas simply bubbles through the liquid.

Random - 24-9-2010 at 01:54

So this reaction is not profitable. Thanks for explanation. I guess I will try to make NH4OH with reaction of calcium ammonium nitrate fertilizer with NaOH solution and then bubble the gas through water.

mewrox99 - 24-9-2010 at 02:06

That will produce an ammonia solution. You will need to titrate it to find it's concentration since there will always be loss

[Edited on 24-9-2010 by mewrox99]

blogfast25 - 24-9-2010 at 13:04

Quote: Originally posted by Random

So this reaction is not profitable. Thanks for explanation. I guess I will try to make NH4OH with reaction of calcium ammonium nitrate fertilizer with NaOH solution and then bubble the gas through water.

Or get garden fertiliser ammonium sulfate. Add a little water to wet it and add a slight excess of solid NaOH. This generates nauseous amounts of NH3, so use an air tight apparatus and lead the NH3 straight into water in which it dissolves completely...

mr.crow - 24-9-2010 at 18:59

Quote: Originally posted by woelen

Making ammonia from H2 and KNO3 in theory cannot be done. What can be done, however, is making small amounts of NH3 from KNO3, NaOH and Al.

Ah yes, this is the reaction I discovered by accident!

Random - 24-9-2010 at 23:18

Quote: Originally posted by blogfast25

Quote: Originally posted by Random

I can only make naoh solution with Na2CO3 and Ca(OH)2. Is there a way to make solid crystals of naoh from freezing that?

12AX7 - 24-9-2010 at 23:30

H2 should reduce KNO3 at high temperature, possibly while molten.
KNO3 + 4 H2 = KOH + 2 H2O + NH3
Notice the large amount of H2 burned. This reaction produces an awful lot of heat and is a terrifyingly bad method of making ammonia. Sourcing the hydrogen from aluminum metal is even more disgusting.

This assumes you don't make an awful lot of N2 gas instead:

2 KNO3 + 5 H2 = 2 KOH + 4 H2O + N2

This competing reaction suggests an excess of H2 should be used. Burning KNO3 grains in an H2 atmosphere would probably result in total decomposition, so a hot solvent-mediated route would be needed, maybe a low melting salt eutectic with a minimum of nitrate in solution. Or, the aqueous method, which probably is assisted by catalytic activities (at the metal surface, by solvation energy, etc.).

Tim