Sciencemadness Discussion Board

Help! I lost my stir bar for tomorrow

Number 9 - 19-6-2012 at 13:58

I have a project to do but I lost my stir bar.

I can use iron, which is magnetic and this really works on a magnetic stirrer.

The point is that I must use it to stirr mixed acid (conc. sulfuric acid and 68% HNO3). So, I suppose that this simply dissolve in this mixture.

What can I do to protect my iron magnet. Is a silicon layer a good option?

For industrial magnets they use teflon, but as a result of the high melting point, I think it's weird to use.

Any troubleshooters who can help me?

Thanks in advance!

Lambda-Eyde - 19-6-2012 at 14:49

Postpone the project, order a new stirbar. Buy more than one so you won't have to delay syntheses for such banal reasons anymore...

dann2 - 19-6-2012 at 15:10

Wrap a bar magnet (or piece if Iron of your stuck enough) in plumbers teflon tape. I believe it works.

ScienceSquirrel - 19-6-2012 at 16:15

Your best option could be to seal a small bar magnet in a thick glass tube.
They used to be available commercially and I used to use them for difficult reactions that would attack teflon.
They worked well as long as they spun rfegularly at low speeds, if they broke free they could be disastrous as they might bounce off the sides of the flask and shatter.

cyanureeves - 19-6-2012 at 16:21

get a piece of nail or screw and push it into an empty plastic bic pen and melt both ends shut.

Sedit - 19-6-2012 at 18:38

Coat a bar magnet in Epoxy, I have done this many times.

Teflon tape will unravel do not try it.

kavu - 20-6-2012 at 00:38

Non-chemically inert plastics are not a good idea as Number 9 stated to be using it for a nitration mixture. For such reactions a good commercial stirbar would be more or less the only way to go. Another method would be to use an overhead stirrer with a glass/teflon stirhead.

[Edited on 20-6-2012 by kavu]

Number 9 - 20-6-2012 at 06:08

I agree with kavu. It is scientific proven that an empty plastic pen filled with iron and coated with epoxy doesn't work for nitration of chlorobenzene to 4-nitrochlorobenzene. The black stirrer bar was 'gonnna with the wind' after less then one hour. Madscience!

IMAG0300 - kopie.jpg - 49kB IMAG0314.jpg - 38kB

[Edited on 20-6-2012 by Number 9]

kavu - 20-6-2012 at 06:51

There's a great safety risk involved when unknown mixtures of organic material are allowed to nitrate. The reaction might have gone out of control and now you have a gunky mixture of all sorts of nasty nitrated stuff, ouch :/