Hey all... I wanted to share a really cool lab I made up last week that was a big hit. I'm sure I'm not the FIRST person to do this, but I know I've never read it anywhere. You can use iodine solution (either bought from a science supply company or prepared from tincture you get at the drugstore) and aquarium water de-chlorinator to react with one another. I used 200 ml of water in a flask. Put in 5 ml of iodine sol. The kids hypothesized how much de-chlorinator it would take to clear the iodine water. Try using 1 drop of de-chlorinator. Swirl flask. Record color change. Keep adding 1 drop at a time until water clears. Be sure the kids are stirring or swirling with enough energy to evoke the chemical reaction. Then continue upping the iodine (new water each time) and then see if the # of drops of de-chlorinator remains congruent with the increase in iodine. This was a really fun lab because the kids got water to change from clear (plain) to reddish-orange (adding the iodine) and then through several shades of yellow (as they added drops of de-chl.) to finally crystal clear again. Best of all- it's CHEAP!!!