For decorations and food from this party, go to THIS post.
I borrowed ideas from every science party blog/website I could find! Pinterest helped a lot with this. I searched for "science birthday party" and "mad scientist" for the most part. My husband is a science buff and he planned out all the the experiments.
We started by having the kids pick a lab partner. We had enough adults helping to assign one to each lab partnership. That worked out really well. We even hired a few high school kids to help us- and paid them in party food. :)
Each scientist had a tray to do experiments in that were messy. We bought a 30 pack from Sam's club of the trays. They also each had a baby soda bottle, goggles, film canister, and petri dish.
As the kids arrived we had them make marshmallow molecules.
They would watch a demonstration of each experiment, and then go do it.
Shaving cream and food coloring to dye paper. This was a MESS. They loved it. All of their lab coats were covered in food coloring. (comes out with bleach :). I wouldn't recommend it, at least not as the first experiment.
Blowing up balloons with baking soda and vinegar
The favorite experiment was shooting film canisters up in the air with water and alka-seltzers. This went on for a good 20 minutes.
We did ph indicators with red cabbage juice
Blew bubble with dry ice smoke
Learned why you never seal up dry ice in a container
Used an air cannon to learn about air drafts
We even filled it with fog machine smoke and blew smoke rings. The kids preferred being hit with a blast of air.
And we did the mentos and diet coke experiment- of course!
We sent the kids home with a lab coat and googles, name badge, baby soda bottle, mini air cannon, mentos experiment mento holding tube (pvc pipe with a pin in it), syringe, pipettes, film canister, measuring spoon, and petri dish.
It was a lot of fun, and oh so messy!!