The_Natural
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Magnetic stirring in a 5L Flask
Before I make the acquisition.
Will I be able to magnetically stir non-viscous reactions fluids of total volume 2-4 L adequately in a 5 L round bottom reaction flask??
At about what volume is mechanical stirring recommended, strictly talking low-viscosity, homogenous reactions here.
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gsd
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I use magnetic stirrer routinely for 2 liter beaker with about 1.5 liter liquid. It gives very vigorous stirring. My guess is it will maintain good
degree of stirring up to about 2.5 lit volume.
For a RB flask you need to consider one thing. The stirrer magnet is short cylindrical bar coated with Teflon and has a small girth ring at the
center. in FB Flask or Beaker, the magnet pivots nicely on that girth ring. However in a RB flask, due to curvature at the bottom it is possible that
the ring may not touch the bottom and magnet will balance on to ends. In that case it will not work.
Otherwise I do not see any problem.
gsd
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BromicAcid
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You can use a magnetic stirrer in a 100-L RB providing you have the correct equipment. There are a number of variables here though, the thickness of
your mantle (or even if you are using a mantle or a heating bath) along with the size and shape of your stir bar and the type of magnetic stirrer your
have (i.e, some are only for small volumes and have a weak magnet). Depending on what you have you could get good stirring or a feeble decoupling.
In my experience magnetic stirring is recomended whenever you have a non-viscous reaction mixture because it is one less place for air to leak into
the reaction system or for reactants to leak out. It is expecially recomended for high vacuum situations since high vacuum stirrer bearings are
sometimes very expensive and at the least difficult to maintain.
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bfesser
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You can also get egg shaped stir bars specifically designed for use in round bottom flasks.
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stoichiometric_steve
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with ultra strong magnets in the stirrer and stirbar, big amounts are definitely stirrable. i use mechanical stirring exclusively when handling
amounts larger than 1L, though - it provides much better mixing of the liquid.
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The_Natural
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Magnet stirring is indeed adequate, but vigorous it isn't. Mechanical stirring will be the future.
Now.. is there any dangers in using an open flame ie. gas burner to bring this vessel up to distillation temp.. say 100-200 deg C?
Of course I'm not talking about distilling flammables here, more like removing water, AcOH solvents etc.
I'm pretty sure my 200mm effective length liebig will not be able to condense all of the vapors from such an operation either.
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Eclectic
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It's probably safer to use a hot air heat gun. They are very inexpensive at http://search.harborfreight.com/cpisearch/web/search.do?keyw...
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vulture
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What's safer about a hot air gun? It's a common misconception that you need a flame to start a fire. Hot air or a hot surface will also start a fire
once above the ignition point, which will definitely be the case when distilling. A fire involving a hot air gun is even more dangerous because
there's the added hazard of electrocution.
A person in our department suffered serious burns when a flask with ether ignited in an oil bath only lately.
Distilling with a gas burner should be done with a rich flame ofcourse, that is, not too much oxygen, as to lower the flame temperature. This allows
for smooth distilling.
[Edited on 17-3-2009 by vulture]
[Edited on 17-3-2009 by vulture]
One shouldn't accept or resort to the mutilation of science to appease the mentally impaired.
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Eclectic
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More diffuse, lower max temperature and lower thermal stress on the glass
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