Cooling baths to test Mpemba effect

[mrutherford]

My middle school child read the experiment on the Mpemba effect (hot water freezing faster than cold water) and decided to test whether or not the method of cooling will change whether or not he observes the Mpemba effect. He will test our home freezer, a dry ice/acetone bath, and a salt/ice bath as cooling methods. My question revolves around the procedure to use the baths. Using 200 ml pyrex beakers with water at different temperatures, how should he create the dry ice/acetone bath? Dry ice is a new material at our house and I am a little anxious about safety. Thanks for your help!

[deleted-71417]

Hi:

Dry ice and dry ice baths are fairly safe and used in school classrooms all the time: Here is a teaching plan that includes some safety info:

http://www.abc.net.au/science/surfingsc ... plan08.pdf

Here are more conservative views::

http://wwwstatic.kern.org/gems/siscsafe ... dryice.pdf

http://stores.biochem.uiowa.edu/Pages/dryicemsds.html

In short the main safety considerations are few:

1. Dry ice is very cold and will cause frostbite if it contacts bare skin. Use tongs and gloves when handling it. The acetone-dry ice mixture has more risk than just the dry ice as it sticks to skin more easily.

2. Dry ice generates a lot of gas as it sublimes. Do not try to contain it in a sealed container, as the container may explode.

3. Carbon dioxide can displace the oxygen in the air and asphixiate living things, though it is not very poisonous. Use and store it in a well ventilated area. Carbon dioxide is heavier than air, so it can flow downhill and collect in low spots without mixing much with air.

4. Acetone is flammable and mildly toxic. Keep it away from flames and avoid ocntact with skin. When mixed with carbon dioxide it is so cold that very little evaporates so the fire danger is low, coupled with the fact that carbon dioxide tends to put out flames.

With common sense handling it is safe and you really should not have any trouble. Closely supervise your kids while using it and everything should be fine. Here is a YouTube video demonstration with kids:

http://www.youtube.com/watch?v=kLO5SJ2uxEE

Good luck and have fun with the project!

Best regards,


Barrett L. Tomlinson