Interesting vacuum incidents
A while ago while generating my first ever concentrated ammonia solution I ran into some rather bad problems during the procedure. The idea was to
bubble un-dried NH3 gas through 500ml of water with VIGOROUS magnetic stirring. I was generating the gas via NH4NO3 + NaOH in a vacuum flask with
side-arm for my gas hose which led to a glass tube that reached juuuust above the stir bar so that when bubbles came out, they were ripped apart by
the insane stirring. I placed the reactants (in prill form) into the flask and positioned a separatory funnel above charged with distilled water.
I added first a small bit of water because this is all you really need for decent reaction speed. Everything was going smoothly and I thought
"oh hell, why not add a tiny bit more water?" So I did and I noticed that even though I only added probably a ml or so, there came back a
VIOLENT suction which took up most of the 500ml I was bubbling gas into and brought it right into my rxn flask (this was the last time I tried gas
experiements w/out a trap) and the reaction wnet crazy obviously. I got some of the mixture on me but it really didnt do anything except mess up my
work area.
I got to thinking why this could have happened and I have determined that what must have occured was that when I added that little bit of distilled
water to the flask which now contained an NH3 atmosphere, the NH3 gas reacted violently with the water and instantly dropped the pressure of the flask
hence sucking up my solution and causing general mayhem.
This got me thinking. I think it would be quite easy to set up a vacuum generation system with only minimal effort utilizing this reaction. Let a
good deal of NH3 build up in the system to purge it of air and make sure that very little NaOH is left in the reaction mixture (easy to figure out).
Next using a dropping funnel, let in a bunch of water that will instantly suck the NH3 out of the chamber and into solution dropping the pressure of
the system which would then be able to be hooked up to something else.
Granted this wouldn't exactly be useful for much but trivial fun but it is an interesting principle to note and perhaps can be utilized by
someone without an aspirator or pump. I happen to have a nice pump so this isn't something I'll be working on making into a practical
device but I think it would be neat to use a meter to figure out how much vacuum can be created when using distilled water, dilute or conc. HCl, other
acids, or maybe alcohols and what not. All of it would depend on NH3's solubility in the medium introduced but you get the picture. Other gases
would be neat too...maybe Cl2 vacuum, H2S vacuum, etc, etc.
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