There are lots of great hands-on ways to explore chemistry with kids. (I cover them in these posts: States of Matter, Mixtures, Reactions.) Here are two of our favorites. (And be sure to check out Oil and Water.)

Milk Fireworks

• Take a flat shallow dish, pour in a thin layer of whole milk – just enough to cover the surface of the dish is plenty. It’s important to use whole milk, not skim – you need the fat!
• Drop on a few drops of different food colors, near to each other – they mostly float on the surface of the milk, since the water-based colors are less dense than the milk.
• Using an eyedropper or pipette*, gather a little dishwashing detergent (Dawn and Joy work well), then drip a few drops of detergent onto the food coloring.
• The colors will fly away from where you added the detergent. (Do a web search for “milk fireworks” to see images or video of the reaction in action!) Once the reaction slows down, drip some detergent somewhere else – a new reaction begins.
• Steve Spangler explains the science of milk fireworks here.

*Most online directions use a q-tip instead of an eyedropper – they dip it in detergent, then dip it in the milk near the food coloring. This works fine, if you dip it and hold it there, not moving, waiting for the fireworks to start. We have found that most three and four year olds stick the q-tip in and stir, and this means the firework effect is nowhere near as dramatic. They do better with the eye dropper method.

Once the reactions have slowed down, you can gently stir the milk and the colors will swirl around, creating a marbled effect.

Art – paper marbling. You can also capture the results of the milk fireworks in beautiful marbled paper. This works best on an absorbent paper, like watercolor paper, construction paper, or even paper towels can also be an interesting effect. BEFORE you do your milk fireworks, cut out squares of paper that fit well into the container you’ll put the milk in. AFTER you’ve done milk fireworks, take a piece of paper, lay it carefully flat on top of the milk. Press down lightly, just to make sure it’s in contact with the surface of the milk. (Note, children tend to press hard enough to sink it, so be clear in your instructions.) Then lift it off by peeling up from one corner, flipping it over as you do. Set it aside to dry. See pictures at Babble Dabble Do and Childcare Network. You might worry the paper would smell of soured milk later, but we haven’t found that to be the case.

Slime

Slime is all the rage of “mad science” parties everywhere, so it’s likely your child will make it many times throughout their childhood. There are TONS of recipes and variations if you search online. Here’s one that works for us:

1. Pour ¼ cup of glue into a plastic cup.
2. Pour ¼ cup of water into glue. Add 4 drops food coloring. Mix well.
3. Sprinkle in ¼ teaspoon of baking soda. (Optional: glitter.) Mix well.
4. Add 1½ teaspoons of saline solution. Stir FAST to combine.
5. When it starts to pull away from the sides of the cup, put just a few drops of saline solution on your hands and rub them together, then pick up the slime and knead it for a little while.
6. Once it’s solidified into a nice not-sticky slime, play with it.
7. When you’re done playing with it, put it in a Baggie to store for later.

Materials notes, with affiliate links: For the glue, we do 20 or 30 batches in one day for all our kids, so I buy a gallon of Elmer’s clear glue. You could also use their Color Changing Glue, Glitter Glue, or Metallic Glue or just their regular everyday school glue for a pastel slime. The contact lens saline solution MUST contain boric acid and sodium borate. Brands we’ve used: Renu Fresh, and Bausch + Lomb Sensitive Eyes.

What’s happening, kids’ version: Glue is made up of long strings of molecules that slip and slide past each other easily. When we mix in the saline  solution, chemicals in there tangle up those strings into this gooey mess.

What’s happening, for adults: The glue contains polyvinyl acetate, a strong and flexible polymer made up of long, repeating, identical strands of molecules. These strands slide past each other easily, making it easy to pour glue. The saline solution has sodium borate and boric acid. When it’s added to glue, the borate ions mix with the glue and connect the long strands together, cross-linking the protein molecules and borate ions so they can no longer easily slide past each other. They tangle and mix together

Some children LOVE slime and want to ply with it for hours. Some enjoy making it but then never touch it again. I don’t love the environmental impact of slime (it’s basically a big hunk of plastic goo) so we make small batches. I also hesitate to use glitter, since it’s little pieces of plastic. We generally avoid it in our class, but this is one project where I use just a little. I have not tried biodegradable glitter here, because it will degrade over a few weeks in this moist environment, I think.