Maybe I should have saved this one for last because it might be the coolest of the five investigations. It looks a little messy, but it doesn't have to be. All's well until you drop in the Alka Seltzer tablets... then the fun begins!
TIP: To cut down on the messy part, just don't fill the bottle too close to the top. Easy fix.
In this lesson, the children discover that oil and water do not mix and they learn why. As they observe the water sinking and the oil floating, they also begin to understand that different liquids have different weights. The next part of the investigation includes a chemical reaction, so we use red food coloring and sequins to make the reaction more visually noticeable. Adding an antacid, like Alka Seltzer, releases carbon dioxide into the liquid allowing the water to float and sink inside the bottle... a lot like lava lamp bubbles do. It's pretty cool. Take a look.
You can see why the kids go nuts for this investigation! It actually doesn't bubble over that much. Again, you can easily control that by leaving a little more room at the mouth of the bottle. To be on the safe side, though, I recommend placing the bottle on a paper plate or in a bowl.
Depending on your budget, this science investigation can be done as a whole class teacher-demonstration with just one large soda bottle. However, if you can get donations, it's more engaging if small groups or each individual can make their own. In the video above, I used baby oil because it's clear, but you can keep the cost down by using store-brand cooking oil instead.
The directions for this investigation, along with the student recording sheets and anchor chart pages, can be found in my Valentine Science pack.
Happy teaching! :)