### Lab Safety

Always wear eye protection during science experiments. Never handle sharp objects, open flames, chemicals, or other dangerous objects without adult permission and supervision.

In this demonstration, we're going to take a closer look at a few cool scientific principles: density and hydrophobicity (don't worry, it's a lot simpler than it looks!). And, using our newly acquired scientific knowledge, we're going to create an awesome lava lamp that really works.

Density is a measure of how much mass a substance contains per unit of volume. For example, the density of water is about 1 gm/mL. This means that if you have say, 5 mL of water, you have just about 5 g of water. Pretty cool, right?

That crazy word from before, hydrophobicity, simply means how hydrophobic or water repellent a substance is (hydro-, meaning water, and phobic-, meaning afraid of). The opposite of a hydrophobic substance is a hydrophilic, or water-loving, substance.

If you haven't done a similar science experiment before, you might've already witnessed a hydrophobic substance meeting up with a hydrophilic one at your dinner table: many salad dressings contain both oil and vinegar and, after they've been sitting around for a while, separate into two distinct layers. What decides where each layer will end up (top or bottom)? You guessed it: density!

## Procedure

1. ##### Step 1

Using the funnel, pour enough water into the bottle so that it's about a quarter of the way full.

2. ##### Step 2

Again using the funnel, pour vegetable oil into the bottle, over the water, so that there's a centimeter or two of space remaining at the top.

3. ##### Step 3

Take a second to observe your lava lamp. Is the oil and water combining? Why do you think that is?

4. ##### Step 4

Now, put about ten drops of food coloring into the bottle and observe again. Does the food coloring seem to be affecting the oil or the water more?

5. ##### Step 5

And finally, the fun part. Snap your Alka Seltzer tablet in half (as best you can) with your fingers. Put one half into the bottle and observe as the reaction it creates propels the "lava" through your homemade lava lamp.