An easy, summery chemistry experiment for kids who don't mind making a mess: chalk explosions! I did this activity with the next door neighbors, whose mom used to be my baby sitter! The girls were 4 and 6 years old.
- Ziplock bags (use the flimsiest ones you can find!)
- Baking soda
- Food colouring
- Corn starch
- Funnel (optional)
- Chalk (optional)
Kids get the hang of this activity really quickly, but they do need adult help.
Give each child a plastic bag and have them add baking soda and cornstarch. You'll want a lot of baking soda for explosion purposes and a lot of corn starch for consistency purposes, but I find it's good to start with an even amount of each and then allow kids to experiment with levels on subsequent explosions.
Add a few drops of food colouring and have the children massage and mix through their powder. This isn't critical, but it's a good measure to make sure you don't get overwhelmed with explosions. Plus most kids love it.
Now, the children need to seal their bag as well as possible, leaving a small opening for adding vinegar.
Go to where you want the explosion to happen, add the vinegar, and seal the bag as quickly as possible. You may want to use a funnel, but we ditched ours very quickly.
As long as you seal the bag quickly, it shouldn't explode instantly. Toss the bag and watch it grow/explode/spray out.
Do it all over again. If you want, add some crushed up chalk to the equation -- it is slightly basic and should react with vinegar as well.
If your explosion doesn't go well, and even if it does, you'll notice that there is a wonderful gooey residue in the bag. It's oobleck! A non-newtonian fluid that is just WONDERFUL for physical experimentation. We poured ours into cracks in the sidewalk between feeling it. I'm deeply in love with how this activity incorporates pressure (which increases until explosion as the chemical reaction releases gas), acids and bases, volume (watch the bag expand! It wants to take up more space), and a bit of neat colour science/newtonian physics, if you so choose to include it).