STEM Tuesdays: DIY
Density Bottles

For today’s activity, we’re going to explore density using oil and water, then learn about oil spills as a part of our Earth Week blog posts.

Materials & Instructions

A clear plastic bottle with a lid
Water
Oil – vegetable oil, olive oil, or baby oil
Food coloring (optional)

STEP 1: Fill the bottle about halfway full with water. If you have food coloring, you can add a drop or two now and mix it into the water for some extra contrast.
STEP 2: Next, fill the bottle the rest of the way (leaving a little bit of room at the top) with oil. We found that mineral oil tends to stay suspended in the water for a longer period of time, while vegetable and baby oil separate from the water more quickly. 
STEP 3: Cap the bottle tightly and shake it until there are oil bubbles mixed in with the water, then put the bottle down and watch as the oil and water separate.

What Happened?

The first thing you might have noticed is that the water formed a layer on the bottom and the oil formed a layer on the top. Why is this? Oil and water have different densities. Water is denser than oil. That means that water molecules are packed together more tightly than oil molecules. Because water is denser, water floats to the bottom while oil floats to the top.

When you shook the bottle, you might have noticed that the oil and water wouldn’t mix together. The oil quickly escaped to the top of the bottle. Another reason oil and water stay away from each other is that oil molecules repel water molecules. Oil molecules are called hydrophobic or “water-fearing” molecules. When we shook our bottle, the oil molecules ran away from the water molecules as soon as possible!

Oil Spills

Have you ever heard of an oil spill? Oil spills happen when humans spill huge amounts of oil (like gasoline) into the ocean. This is a form of pollution. The oil spreads out over the surface of the water – because density! – and can be very harmful to the environment. The oil contaminates the water, hurts the fish and other ocean animals living inside the water, and even coats bird wings so that they cannot swim or fly.

Vocab Words

Density: how tightly or loosely items are packed together. Water molecules are packed tightly together, so they are very dense. 
Molecules: A teeny tiny group of atoms that are bonded together. Molecules make up everything around us!
Repel: To push away.
Hydrophobic: Things that are hydrophobic (like oil molecules) don’t like water – they push it away. Hydrophobic means “water-fearing.”
Pollution: When something harmful, like oil or trash, is introduced to the environment. 

Oil spills are one reason that some animals, like African Penguins, are endangered. It’s very important to clean up oil spills as fast as possible. Want to learn more about African Penguins and how oil spills are cleaned up in order to save the oceans and ocean animals? Check out Georgia’s Aquarium’s Deep Sea Learning Oil Spill Cleanup project for a great at-home learning activity.