Chemistry Blog

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Apr 15

Magnetic grapes and NMR

by Mark | Categories: chemical education, fun, Uncategorized | (10879 Views)

When I was an undergrad I found NMR to be one of the trickiest techniques to get my head around. I think it was because the technique involves so many concepts that run counter to everything we’ve learnt before. After all in school we get told about ferromagnets and thats it. Then at uni suddenly someone is trying to tell us that actually there’s these other things called diamagnets and paramagnets, which means that even water is magnetic!

So now that I get to teach NMR I like to demonstrate diamagnetism right from the get go. Of course diamagnetism is really weak so you need a precision built, low friction setup. So I set about building one with ….

  • 2 grapes
  • A wooden skewer
  • A pin
  • An old film canister
  • A neodymium magnet. I get mine from emagnets. The stronger the better I use  one with 20 Kg pull.
Safety:
THIS IS REALLY IMPORTANT
The neodymium magnets are really powerful. So…
  1. Don’t let kids play with them.
  2. Don’t put them near your credit cards, phone, watch or any other electrical equipment.
  3. Don’t put 2 magnets anywhere near each other because they’ll fly towards one another, shatter and send chunks flying.
  4. If you have any medical implants don’t go anywhere near them.
  5. Read the safety instructions that come with the magnets.

The Build:

1. Push the 2 grapes onto either end of the skewer

2. Push the pin through the cap of the film canister, so that its pointing upward. Put the cap back on the canister.
3. This is the tricky but. You need to balance the skewer and grapes on the point of the pin.
4. Once you’ve managed that just put the edge of the magnet near one of the grapes and watch it spin.
There you go, the magnet repeals the water in the grapes and you have a nice down to earth demo of diagmanetism.

http://youtu.be/-zOzEvHmaK8

Then to cap it off show your audience the levitating frogs, and I promise they won’t forget diamagnetism after that.http://youtu.be/A1vyB-O5i6E
Originally posted (in a slightly different form) at http://www.t2ah.com/

2 comments

  1. Ian

    Well, I learned some new there -the levitating frog is brilliant!

  2. tevetorbes

    As a corollary to this, you can use your same strong magnet and a bit of liquid oxygen to demonstrate paramagnetism.

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