optragon
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Acetic acid not neutralised by ammonia?
Hola amigos,
I'm puzzled by acetic acid residue that should have been neutralized by ammonia. Working on a Liquid-liquid extraction and to the aqueous acetic acid
solution NH3 is added to reach a pH of 9.5. Strangely, after distilling off the organic phase, there is quite some acetic acid left over (determined
by smell). How can that even be at pH 9.5?
I can only think of the pH electrode being inaccurate, but I don't have a new one at hand until next week. What do you think? Any other possibility?
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hissingnoise
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Ammonium acetate actually does smell of acetic acid, as a result, probably, of its hygroscopicity . . .
Anyhoo, welcome to scimad!
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optragon
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Aha! That might be exactly what is happening. I was thinking it doesn't quite smell like clean acetic acid... Thanks a lot for the input!
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blogfast25
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Quote: Originally posted by optragon  | Hola amigos,
I'm puzzled by acetic acid residue that should have been neutralized by ammonia. Working on a Liquid-liquid extraction and to the aqueous acetic acid
solution NH3 is added to reach a pH of 9.5. Strangely, after distilling off the organic phase, there is quite some acetic acid left over (determined
by smell). How can that even be at pH 9.5?
I can only think of the pH electrode being inaccurate, but I don't have a new one at hand until next week. What do you think? Any other possibility?
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By all means check your meter (regularly) but ammonium acetate undergoes hydrolysis:
NH4<sup>+</sup> + H2O < ==== > NH3 + H3O<sup>+</sup>
OAc<sup>-</sup> + H3O<sup>+</sup> < ==== > HOAc + H2O
Both perfectly neutralised ammonium acetate solutions and solid ammonium acetate always small of vinegar (acetic acid, aka ethanoic acid).
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Praxichys
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Also, ammonium acetate readily loses water under gentle heating to form acetamide.
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PlatinumLab
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Heating ammonia salts, or even other salts where one component is a gas, can cause that gas to leave the solution. In principle it is extremely
common. I think something like this was one of the very first labs I had done in class years ago.
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DrMethyl
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^^
Welcome to sciencemadness 
[Edited on 27-1-2016 by DrMethyl]
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