Rainbow Experiment

April 26, 2021

Arts and Crafts

Create a Rainbow in a Straw: A Lesson in Water Density

A good way to keep children constantly curious is by engaging them in activities that will give them the opportunity to practice critical thinking. It has been proven that children with an early interest in science grow up to be successful people that continue to strive until they reach their goals. And early exposure at home will do a lot of good for them. Many parents and caregivers often think that these are cumbersome tasks that require a lot of experience. But these activities are actually fun and easy to do. You don’t need to be an expert in science just to get the same results; and this can actually be a good thing. You’ll have the opportunity to enjoy and learn from the activities the same way children will. 

And to make things even simpler, here is something simple and fun you can do inside your home just by using a good table. This activity is focused on water density and how kids will understand that not all liquids weigh the same. This is a better illustration of how oil and water will not mix and the former will always float on top.  

You’ll need the following:

  • Clear straws
  • Several clear containers of uniform height (these should be shorter than the straw. If you have them, shot glasses will work well with this experiment)
  • Several colors of food coloring (you can use color tablets, liquid food coloring, or a small dab of coloring paste)
  • Popsicle sticks or any stick to mix
  • A measuring teaspoon
  • Sugar
  • Bowl or tall clear container

How to do the experiment: 

  • Start by lining up your containers in a row. Your table must be stable to avoid spillage or accidental slippage. 
  • Fill each container with water about three quarters of the way. 
  • Add coloring to each of the containers and mix it well to make sure there are no residue left from the coloring agent. 
  • Now, add sugar in this order: 
    • 1 teaspoon for the second container
    • 2 teaspoons for the third
    • 3 teaspoons for the fourth
    • Add a teaspoon increment for each of the succeeding containers. Make sure to mix them well and that there are no undissolved particles left.
    • Note that the first container will not have any sugar added.
  • Hold the straw with four fingers and your thumb should be resting on the top of one end like a cover. 
  • Without releasing your thumb from the straw’s opening, slowly plunge the straw all the way to the bottom of the first container. 
  • Quickly lift your thumb from the top for just a second and put it back down to cover the opening. You’ll notice there will be some of the first colored liquid inside the straw. If you lift your thumb, the liquid will be released once more. Your finger acts like the vacuum that holds the liquid in place inside the straw.
  • Keeping your thumb in place, plunge the straw in the second container and release for a second before closing it again. Lift the straw and you should see there are now two colors inside the straw but are not mixing together. The colors will still be distinguishable. 
  • Proceed to do the same steps until you reach the last container. And at this point, you have created a sugar rainbow.


Now, to demonstrate the vacuum you created with your thumb, hold the straw over the spare bowl or clear container and release your thumb. Watch as the liquid fall right in, creating a swirl of mixed colored liquid. 

It would be a great idea to do it yourself first before you let the children try. This way, you’ll have a better grasp at how the whole experiment works and you’ll be able to easily explain the process to them. When you’re ready, demonstrate each step to them and have them do the same thing you just did. So you’ll all finish around the same time.

A few tips:

Before you begin with the demonstration, ask your children if they think all liquids weigh the same. Take note of their answers. Let them examine the containers of differently colored liquids (Make sure you haven’t added the sugar yet. They need to see this part to help them come up with their own hypothesis later on). Give them one clear straw each and ask them how they can get the liquids inside the straw without using their mouths. Again, take note of their answers. This is probably the most important tip of all: every answer is valid, even silly answers are good answers. This is simple proof that they are practicing critical thinking. 

Without adding the sugar to the containers, demonstrate the concept of a vacuum to the children with the use of the straw and your thumb. Move some of the liquids in smaller containers and ask them if they can create a layer inside the straw. You can illustrate the concept with the use of paper and crayons. Whatever they suggest or do will likely end in failure. Here, you can explain that it’s because all these liquids weigh the same. 

Now, add the sugar increments and proceed to do the actual experiment. After one round (you’ll all likely want to do it another couple of rounds), ask them what they think about the activity and if they had fun doing it. Then ask why they think it was possible to layer the colors this time. Then explain that by adding some sugar in increasing amounts to each liquid you were able to increase the water’s density or weight. Feel free to keep doing the activity a few more times while you’re discussing your observations.

Clean up is fairly easy to do, you can even get the kids involved. One last fun activity you can do is to try and layer the colors in a new container. Instead of vacuuming the liquid inside a straw,  use a long medical dropper or turkey baster to try and layer the liquids in a new container using the same sequence from the non-sugar liquid to the last one.

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