Sciencemadness Discussion Board

White dust everywhere!?

spong - 26-3-2011 at 23:58

After finally getting some glacial acetic acid, I tried to make some anhydrous ammonium acetate as I'd read a bit about it on here. I bubbled NH3 through it, it heated up quite a bit and the gas addition was stopped when the AcOH turned to a slush. I didn't really have any use for it so it just went into the dessicator (the reaction was mainly a test of a new way I'd planned to handle NH3 which didn't work too well... Ammonia gas hurts!)
Now it's been sitting there for a few months and I've remembered about it and gone to get it out and there's a white dust everywhere, coating the jar it was in, the filter paper some of it was on and the crystals themselves.
What would this dust be? The drying agent was CaCl2 and the box still sinks of acetic acid if that makes any difference but the crystals weren't in contact with the CaCl2 so I don't see how a reaction could occur.

[Edited on 27-3-2011 by spong]

Jor - 27-3-2011 at 00:15

Well. It is....... ammonium acetate!

Remember the ammonium-ion is a weak acid, and acetate-ion is a weak base. So:


Both ammonia and acetic acid are volatile, but because it is a closed jar they can recombine somewhere else in the jar. When this goes on for long enough you will have ammonium acetate coating your entire jar.

spong - 27-3-2011 at 00:25

Oh I didn't think of that, just like NH4Cl does! :P I was worrying about a reaction between the CaCl2 and acetate.
Doesn't this mean that there could also be a reaction between the NH3 and the CaCl2 as well? They form a complex don't they?