A stratified science project from Science Buddies

Key concepts Physics Chemistry Density Liquids

Introduction You probably know that when solid objects are placed in liquid, they can sink or float. But did you know that liquids can also sink or float? In fact, it is possible to stack different layers of liquids on top of one another. The key is that all the different layers must have different densities. You can stack them by picking several liquids with a range of densities or by varying the density of one liquid by adding chemicals such as sugar or salt to it. If you choose colored liquids or add food coloring to each layer, you can even create a whole rainbow of colors in one single glass! Want to see for yourself? In this science activity you will stack several liquids—one by one—and create a colorful density column!

Background Whether an object sinks or floats depends on its density compared with the density of the liquid into which it is dropped. All types of matter—solids as well as liquids—are made up of many different atoms. Depending on the mass of these atoms, their size and the way they are arranged, different substances will have different densities. The density is characteristic for each individual compound and defined as the mass of a compound divided by its volume. In other words, the more matter there is in a certain amount of volume, the denser a substance is. One cubic centimeter of rock, for example, is much heavier than a cubic centimeter of wood. This is because there is much more matter in the same volume of rock compared with the wood.

Liquids can also have different densities. Freshwater, for example, has a density of about one gram per cubic centimeter at room temperature. Any compound—liquid or solid—that has a higher density than water will sink whereas substances with a lower density than that will float. You can test that for yourself by gathering several liquids that you have in your kitchen such as vegetable oil, corn syrup, dishwashing soap, water, rubbing alcohol and more. Which one of these do you think will sink or float in water? Find out in this activity!

Observations and results Did you successfully stack all three liquids on top of one another to create a colorful density column? It actually does not matter in which order you add the three different liquids into your jar; the layers will always end up being the same: The corn syrup settles on the bottom, the colored water is in the middle and the vegetable oil floats on the top. This is because corn syrup has the highest density of all the liquids, about 1.4 grams per cubic centimeter whereas the density of water is about one gram per cubic centimeter at room temperature. Vegetable oil is lighter than water with a density of about 0.9 gram per cubic centimeter and thus floats on top of the water. Even if you turn the jar upside down, the layers rearrange to the original order due to their different densities. If you did the extra activity and weighed the same volume of each liquid, you should have found that corn syrup was the heaviest, followed by water and then the vegetable oil.

The objects that you dropped into jar 2 settled in the density column depending on their own densities. The rubber band probably settled on top of the corn syrup whereas the penny fell all the way to the bottom of the jar. The wax should have rested on top of the water layer and the popsicle stick should have floated all the way on top of the vegetable oil. Finally, if you shook the jar really hard, you might have observed that the vegetable oil still separated and floated on top, but the corn syrup and the water layer started to mix and did not separate very easily anymore. This is due to the miscibility of the different liquids. If liquids have a very different chemical structure that makes one polar and the other one unpolar, they will not mix and always stay separate. This is true for oil, which is an unpolar liquid, and water, which is a polar liquid. Corn syrup, on the other hand, has the ability to mix with water and thus can dissolve in it. This is what happens when you shake the jar really hard.

You can try many more objects and liquids to create even more layers; it is just a matter of density that will determine where they settle in your density column!

Cleanup You can pour all the liquids from the jars down the drain. Clean any spills.

More to explore Density of Matter, from Ron Kurtus’s School for Champions Ocean Density, from Science Learning Can Water Float on Water?, from Science Buddies Science Activity for All Ages!, from Science Buddies

This activity brought to you in partnership with Science Buddies

Rodney E. Rohde and The Conversation US

Benjamin Storrow and E&E News

SPACE.com and Josh Dinner

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