Test Tube Rainbow - Exploring the Density of Liquids

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Students will be able to understand how liquids have differing densities by participating in an investigation.

Big Idea

Solids have different densities, but so do liquids! This fun investigation will help your students understand this fascinating concept.


30 minutes

Materials Needed for Each Group:

  • Honey
  • Corn Syrup
  • Dish Detergent
  • Water (with food color added)
  • Cooking Oil
  • Recording Sheet
  • Large Test Tube 

Materials Tip: You can use some other type of clear container if you do not have test tubes available.  The test tube makes the experiment economical, as you don't need a lot of each ingredient.

This is a more open ended inquiry-style investigation.  The students will have the opportunity to participate in the investigation, then we will discuss and make sense of what they observed.

I have a table in the front of the classroom and I have the 5 different liquids displayed on the table.  I show the items to the students, holding each one up so they can see them.  I say to the students, We are going to be putting these five things into our test tubes, but before we do, what do scientists usually do before they begin an investigation? (shouts of make a prediction).   That's right, they make a prediction.  I want you to take your recording sheet and draw a picture of what you think the test tube will look like when we add all of these things to it.

The students make their predictions and draw the picture to go with it.  When they are done, I distribute one test tube to each group.  I circulate around the room with the container of honey and allow the students to squeeze the honey into the tube.  I assist them so the honey goes directly into the center of the tube, not along the sides (no worries if it does though, with a little tapping, it will make its way to the bottom of the tube).

We continue adding the ingredients to the test tube in the order listed above.  When all the ingredients are added (photo), I have the students draw what the test tube looks like.  See work samples:   Work Sample 1  Work Sample 2   Work Sample 3                                                                                   


10 minutes

To help the students make connections to what we experienced today and to what we have learned about density, I ask some questions.  Here are some questions to ask:

What happened to our tube?

Were your predictions correct?

Why didn't the different things mix together?

What have we been learning about?  Do you think density has a role in this?  Do you think these liquid have the same density?  How do you know?

The discussion is really steered by what the students bring up.  Here is a video clip of some of our discussion.


10 minutes

Materials Needed:

  • Clear Glasses
  • White Milk
  • Chocolate and/or Strawberry Syrup
  • Plastic Spoons

To wrap up our lesson, I wanted the students to make a connection between our learning and something that is part of our every-day life.  I brought in chocolate syrup and clear glasses for our snack.  I poured the students' milk into the glasses and I ask them to make a prediction with a neighbor as to what will happen when the syrup is added to the milk.  I ask a few groups to share their predictions aloud.

I then put the syrup in the milk without stirring it.  I have the student check to see if their predictions are correct.  I point out to the students how the things we learn in our science lessons impact the world around us and I encourage them to look for examples of liquids with different densities.

We stir up the milk and enjoy our snack.