Sciencemadness Discussion Board
Not logged in [Login ]
Go To Bottom

Printable Version  
Author: Subject: Magnetic stirring in a 5L Flask
The_Natural
Harmless
*




Posts: 15
Registered: 11-5-2008
Member Is Offline

Mood: No Mood

[*] posted on 14-11-2008 at 17:22
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.
View user's profile View All Posts By User
gsd
International Hazard
*****




Posts: 847
Registered: 18-8-2005
Member Is Offline

Mood: No Mood

[*] posted on 14-11-2008 at 17:33


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
View user's profile View All Posts By User
BromicAcid
International Hazard
*****




Posts: 3047
Registered: 13-7-2003
Location: Wisconsin
Member Is Offline

Mood: Legitimate

[*] posted on 14-11-2008 at 18:24


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.




Shamelessly plugging my attempts at writing fiction: http://www.robvincent.org
View user's profile Visit user's homepage View All Posts By User
bfesser
Resident Wikipedian
*****




Posts: 2114
Registered: 29-1-2008
Member Is Offline

Mood: No Mood

[*] posted on 14-11-2008 at 19:21


You can also get egg shaped stir bars specifically designed for use in round bottom flasks.
View user's profile View All Posts By User
stoichiometric_steve
International Hazard
*****




Posts: 771
Registered: 14-12-2005
Member Is Offline

Mood: satyric

[*] posted on 14-11-2008 at 23:46


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.



View user's profile View All Posts By User
The_Natural
Harmless
*




Posts: 15
Registered: 11-5-2008
Member Is Offline

Mood: No Mood

[*] posted on 17-3-2009 at 04:03


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.
View user's profile View All Posts By User
Eclectic
International Hazard
*****




Posts: 899
Registered: 14-11-2004
Member Is Offline

Mood: Obsessive

[*] posted on 17-3-2009 at 05:40


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...
View user's profile View All Posts By User
vulture
Forum Gatekeeper
********




Posts: 3331
Registered: 25-5-2002
Location: France
Member Is Offline

Mood: No Mood

[*] posted on 17-3-2009 at 14:07


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.
View user's profile View All Posts By User
Eclectic
International Hazard
*****




Posts: 899
Registered: 14-11-2004
Member Is Offline

Mood: Obsessive

[*] posted on 17-3-2009 at 16:25


More diffuse, lower max temperature and lower thermal stress on the glass
View user's profile View All Posts By User

  Go To Top