Chemical Forums
Chemistry Forums for Students => High School Chemistry Forum => Topic started by: pzona69 on January 18, 2008, 03:28:18 PM
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I need regular ammonia for an experiment, as in NH3, but all the household ammonia at grocery stores and everywhere lists the ingredient as ammonium hydroxide. I was wondering, is there a dehydration (I don't know much about inorganic dehydration) reaction to yield ammonia and water, or whether this would separate during a reaction?
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Dear Pzona69;
Do you really need dry NH3 Gas for a Reaction?
Usually in such a case a Cylinder with dry NH3 is indicated.
If you don’t have this possibility you can get it from a concentrated Ammonium-hydroxide solution by slowly heating. In this case you have to pass the gas stream through, for example a “Drying Tower” filled with Sodium hydroxide pellets.
This procedure can be a little tricky, because to get the correct amount of NH3 Gas, and to not overheat the “Drying Tower” by too fast generation.
Maybe there are also other methods to generate it, but in most cases you have to dry it anyway.
I hope it gives you at least an Idea.
Good Luck!
ARGOS++
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If you want NH3 in solution, NH4OH is what you're looking for.
NH3 + H2O (https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2Fwww.forkosh.dreamhost.com%2Fmimetex.cgi%3F%7B%5Crightleftharpoons%7D&hash=f424e97333a9a04a34809754392a3b3e4a45aa0f) NH4OH (aq)
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Yeah, that's what I was asking. I mean, say I had a reaction I wanted to do that included NH3, I would use ammonium hydroxide, and when balancing it, treat it like ammonia plus water, right?
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Not necessarily, in aqueous solution, it would be more like:
NH3 + H2O -> NH4OH -> NH4+ + OH-
The presence of water may alter the chemical reactions that you're trying to perform. Question: What is the reaction you need anhydrous NH3 for? Some people have taken to robbing anhydrous NH3 from anywhere it isn't stored carefully, for use in home meth labs. :(
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Do you really think there are many ammonium ions? Remember the degree of dissociation of a weak base.
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Do you really think there are many ammonium ions? Remember the degree of dissociation of a weak base.
I believe my far right expression describes the nature of "ammonia gas in water" better than the far left one, and that it most matches the concerns the OP is working with.
I recognize the equilibrium should be drawn with bigger arrows pointing towards the center. On that point, how are people drawing that on these forums?
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I guess we are talking about the same. :) Most of the ammonia molecules are just dissolved NH3 (aq).
btw.: What does "OP" stand for?
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I guess we are talking about the same. :) Most of the ammonia molecules are just dissolved NH3 (aq).
Really? Seems odd to me that gaseous ammonia would have much solubility in water without ionizing.
btw.: What does "OP" stand for?
OP is the original post, or original poster. It's also a generalized appeal to bring a thread back to it's original topic. Not that it ever works. :D
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I guess we are talking about the same. :) Most of the ammonia molecules are just dissolved NH3 (aq).
Really? Seems odd to me that gaseous ammonia would have much solubility in water without ionizing.
Why? Formaldehyde doesn't ionize, yet it dissolves even better.
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True enough, dipole movement and hydrogen bonding are enough to dissolve ammonia in water molecularly.
But, I dunno, I was browsing a bit on wikipedia, as a general overview of what the chemistry conventions are, and most people seem to say that ammonium hydroxide is a weak base. And I don't agree, it seems to form a solution of very high pH, which makes it seem strong to me. But then again, with a pKb of 9.25, so yeah, not a very strong base.
Back to the original question, ammonia, dissolved in water, acts like anhydrous ammonia suspended in water? Ummm, no, I don't think so. In any reaction, it's going to behave like NH4+ and OH-, right?
And how do I draw the arrows on the forums?
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I wanted to suggest to include LaTeX or mimeTeX in the forum before, but I failed to install it on a test forum, so I didn't mention it (actually I didn't really tried it hard). You can implement the code using the image http://www.forkosh.dreamhost.com/mimetex.cgi?{\rightleftharpoons}. You have to put it between the [IMG...[/IMG tag. Of course you can use any other code, too.
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You have to put it between the [IMG...[/IMG tag. Of course you can use any other code, too.
Ahhh...now there's an idea. I'll have to build (or find) a few good double arrows, longer and shorter ones, and put them somewhere they'll be ready for embeding.
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Not necessarily, in aqueous solution, it would be more like:
NH3 + H2O -> NH4OH -> NH4+ + OH-
The presence of water may alter the chemical reactions that you're trying to perform. Question: What is the reaction you need anhydrous NH3 for? Some people have taken to robbing anhydrous NH3 from anywhere it isn't stored carefully, for use in home meth labs. :(
I'm not trying to make meth, trust me :). We've been doing a chapter on carboxylic acids in school, and I wanted to figure out the yield of ethanamide from a reaction of ammonium hydroxide and vinegar. I don't know much about amides, other than that this particular one can be carcinogenic, which since finding this out, I have decided against making it at home.
The only reason I chose ethanamide was because I figured it could be produced using common items (which is why I was asking about ammonium hydroxide's reactive similarity to ammonia).
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We've been doing a chapter on carboxylic acids in school, and I wanted to figure out the yield of ethanamide from a reaction of ammonium hydroxide and vinegar.
Estimated yield = 0 %
This is a simple acid/base reaction that yields ammonium acetate.
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That's what I thought at first, that it would just be an acid base reaction, which is why I wanted to isolate NH3.
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The dehydration of ammonium acetate should yield acetamide. It's easier to answer questions if I know from the beginning what exactly you want to do/know.
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Yeah I realize that, my fault for not saying in the original post.
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No problem. It resulted in an interesting discussion about the structures of ammonia in water :)
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Just another thought: In the case of hydrochloric acid the equilibrium is approximately complete on the right side. And does anybody call it "oxonium chloride"? :)