A little vegetable oil and water can provide lots of fun hands-on science learning for kids. (You could also use baby oil, but I wouldn’t if you think your child might decide to taste it…)
Blobs: Put a thin layer of oil in a dish. Give your child containers of colored water and a pipette or eye dropper. They drip water into the oil and watch it pull into little blobs of water. If they stir and the blobs bump against each other, they’ll merge into bigger blobs as you watch. For best effect: Try this in a clear container on a light table, or put a clear container on white paper so the colors are obvious.
The toddler version: for younger children, you can create a sensory bag: fill a ziplock with oil, water, and other interesting items. Tape it closed. Tape it to a table. Let your child pat at it and watch the oil and water bubbles, and watch the items squirt away from where they touch.
Free Exploration: Put out clear containers (a glass, a plastic cup, a water bottle or jar with a lid). If you have a funnel, now may be a good time to teach them how to use one, but it’s not essential. Put a little water in one container and a little oil in the other. They can pour back and forth, stir. If the container has a lid, they can try shaking it to see if they can get the oil and water to combine. Give them food coloring in dropper bottles, or in a container with pipettes or eye droppers. Have them add food coloring to the oil or water, see what happens.
Note: most food coloring is water-based and will blend with the water, but will make little balls of water in the oil. There is oil-based food coloring if you want to add that to the experiment. For the oil coloring, I have used Americolor Oil Food Coloring and Chefmaster Liquid Candy Color. (affiliate links) I like Americolor better, but both of them will stain your water a little as well as coloring the oil, so it’s not as perfect an illustration as I want it to be.
Fireworks in a Jar: Fill a jar most of the way with water, then in a separate container, whisk together oil and regular food coloring till the food coloring is broken up into lots of tiny suspended droplets of color. Pour the oil on top of the water – the food coloring will gradually separate out, sink through the oil, and cascade into the water then mix with the water. Do a google search for “fireworks in a jar” to see lots of examples, including I Can Teach My Child.
Lava Lamp, option 1: After your child has created containers of oil and colored water, spoon a little salt into one. The salt sinks to the bottom, carrying some oil with it. As the salt dissolves in the water, the oil escapes and bubbles back up to the top. If you want more bubbles add more salt.
Lava Lamp, option 2: Try dropping part of an Alka-Seltzer tablet in a container of oil and water. The tablet sinks to the bottom, reacts in the water, making bubbles that rise up through the oil, carrying up some colored water bubbles, that then sink back down. Do a search for “oil and water lava lamp” to see pictures.
Try turning off the lights and shining a flashlight on your “lava lamp” for a fun effect.
Emulsion. Still have a container of oil and water? Is the oil still just sitting on top of the water, refusing to mix in? Try stirring in some dish detergent. What happens?
Oil molecules are attracted to each other and stick to each other. Water molecules stick to each other. But oil and water won’t mix with each other, because water is a polar molecule and oil is non-polar. They are immiscible liquids. If you shake them up, they’ll look like they’re starting to mix, but as soon as you stop shaking, they separate again. Since oil is less dense than water, it will float on top of the water.
Detergent is made of molecules with a hydrophilic (“water loving”) end and a hydrophobic (“water fearing”) end. The hydrophobic end breaks up the oil molecules, and the hydrophilic end connects to the water molecules. Once you’ve added the detergent, the oil and water can be mixed together.