Science experiment ideas? Specifically chemistry

[Fae]

I'm a high school student and my school's Science Day is coming up soon. I'm in desperate need of interactive chemistry experiments that will attract students to come to my booth and not bore them. I was considering working with dry ice, since it was a hit last year, but unfortunately it's already been taken by another group. I considered liquid nitrogen experiments, but after a while I realised they were too dangerous and carried a big risk. 

I'm looking for something that my audience can participate in, something that a lot don't know about (that being said, reactions involving metals is out!). Something similar to the aspect of the dry ice experiments, whereby it's relatively harmless yet intriguing. It would also help if the materials are easily obtained. Please help ASAP!

Edited July 29, 2018 by Fae

[MathGeek]

Tough ask.  You need something safe enough not to potentially harm careless students but interesting enough to attract their attention.

Mentos and soda are a common favorite that fulfills this critera, but it is too messy unless you are outside.

My experience is that high school students usually need something to be at least a little dangerous to be interesting.  Thermite, oxy-acetylene, sugar rockets, and other energetic materials can be made interesting enough, but these are more in demonstration territory and not safe in the hands of careless students. 

Once you add "cheap" and "common materials" to your requirements and you are over constrained.

[hypervalent_iodine]

Making slime is always a hit at open day at my university. It's easy to do, colourful, low risk, and you can talk about cross linking of polymers. Get yourself some plastic cups, paddle pop sticks for stirring, PVA based glitter glue and borax solution (and wear gloves!). You'll find plenty of recipes online for it. I recommend a few different glitter glues if you can, and to practice first (it's easy, but you want to get the volumes right). Some glues work better than others.