This is a fun project that lets kids learn about different liquids and how some don't like to mix. The scientific term for this is
"intermolecular polarity." Without getting too deep into the science behind this, we can just say that water molecules attract other
water molecules and stick together while oil molecules attract other oil molecules and stick together, however, the water and oil molecules
don't attract each other nor do they like to stick to each other.
For this experiment, we emptied out all but about one quarter of a VOSS brand water bottle. We added a few drops of food coloring to the water and mixed it up. Then, using a funnel, we slowly poured in some vegetable oil. You will want to leave a bit of a gap at the top, so don't fill it up all the way.
At this point, you can see the different layers and how they don't like to mix. You can slowly roll and tilt the bottle, but I don't recommend that you shake it. (Shaking the bottle will make the oil cloudy and mess up the next part.)
Now, for the bubbles of color. If you remove the top of the bottle and drop in a half of an Alka Seltzer tablet, you will soon have a bunch of colorful bubbles racing to the top of the oil. Once at the top, the bubble will fall back to the bottom. Have the kids guess at what is going on.
Have they figured it out? Once the seltzer tablet reached the layer of water, it started to dissolve. When it did, it created bubbles of gas. These bubbles started to rise and as they rose, they took some of the colored water with them. Once the bubble reached the top, the gas escaped and left the colored water droplet in the oil. Since the water droplet is heavier than the oil, and we have the intermolecular polarity keeping it from mixing with the oil, it sank back to the bottom and joined the rest of the colored water.
This process keeps going for as long as it takes for the tablet to dissolve. Sometimes, the tablet itself will float to the top with hundreds of little bubbles on it. If you pop enough of those bubbles, the tablet will sink and the process will start over.
You can use the same bottle of water and oil many times, just add another half a tablet and watch it go.
If your local stores don't carry VOSS Artesian Water, you can use about any clear container. Or, you can buy some on Amazon here: VOSS Artesian Water (Still), 330ml Plastic Bottles (Pack of 12)
Likewise, you can find Alka Seltzer here: Alka-seltzer Original Effervescent Tablets