Rainbow in a Glass

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Failed idea! This one is, as you can see, is incomplete. We abandoned it because it did not work in our hands, and we felt would be unlikely to work well in the hands of second graders. The problem we encountered was that the colors mixed rapidly, even with large differences in sugar concentrations. One possible solution might be to run this in test tubes rather than glasses. There would be less potential for mixing in the narrow diameter, and layers could more easily be built up.

The complete directions are to be found at the link below.Declan 12:51, 18 April 2007 (UTC)

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Biology In Elementary Schools is a Saint Michael's College student project from a course that ran between 2007 and 2010 and fully described in this book chapter. The student-created resources have been preserved here for posterity. Link under 'toolbox' for printer-friendly versions of the exercises. Click on handouts to print full resolution versions. Please see Wikieducator's disclaimer, our safety statement, and the Creative Commons licensing in English and in legalese.

Rainbow in a Glass

Student worthiness

This experiment has been tried and but we can't say that we trust this one.

Primary biological content area covered

This activity will expose students to the concept of density and hypothesizing.


  • Four different colors of food coloring (blue, green, yellow, and red).
  • Five tall glasses or plasitc cups
    • 4 glasses should be able to hold at least 1 1/2 cups.
    • 1 glass should be able to hold at least 5 cups.
  • 3/4 cup (180g) of granulated sugar
  • A tablespoon for measuring
  • 4 cups (960 ml) of water (1 cup per color)


Handout . Students worksheet on color hypotheses ; Click to view full size.

Description of activity

In this activity, students have the opportunity to create a rainbow in a glass. The procedure is easy to follow and requires inexpensive materials. This activity relies on the concept of density, allowing a rainbow of separate colors is created in a glass.

Lesson plan

  • Have the students fill out the first part of the handout. They should hypothesize what they think is going to happen in the activity.
  • In glass #1, mix 1 tablespoon of sugar with several drops of food coloring and 1 cup of water.
  • In glass #2, mix 2 tablespoons of sugar with several drops of a different color and 1 cup of water.
  • In glass #3, mix 3 tablespoons of sugar with several drops of a third color and 1 cup of water.
  • In glass #4, mix 4 tablespoons of sugar with several drops of a fourth color and 1 cup of water (sugar should be completely dissolved in each glass).
  • In glass #5, carefully combine the contents of glasses 1-4. First put in the contents of glass #4, then, using a tablespoon, add the contents of glass #3 (make sure the colors do not mix). Then add the contents of glass #2 and finally, those of glass #1.
  • Have students make observations about what occurred.
  • Discuss with the students why the colors don't mix and then have them fill out the rest of the handout (what really happened).

Potential pitfalls

When combining the four color mixtures, use a spoon to add a small amount at a time. If you dump all of the liquid contents on top of each other, the colors will mix instead of floating on top of one another.

Math connections

Students will be using fractions, ratios, and measuring in this experiment. They will need to measure out the appropriate quantity of sugar for each glass, and will also use ratios in comparing the amount of water, sugar, and food coloring used in the activity. Fractions are present in the measuring process, and also in the finished project. Upon completion of the activity, students will see that each color of the rainbow takes up a certain amount of space in the glass.

Literature connections

  • "The Rainbow Fish" by Marcus Pfister
  • "Dora's Rainbow Egg Hunt" by Kristen Larsen and Steven Sawitsky
  • "What makes a Rainbow?" by Betty Ann Schwartz and Dona Turner

Connections to educational standards

Vermont science grade expectations

S1-2:12 Students demonstarte their understanding of the states of matter by....Identifying, describing, and comparing the state of matter of solids and liquids.

S3-4:2 Students demonstrate their understanding of predicting and hypothesizing by....Identifying simple patterns of evidence used to develop a prediction and propose an explanation.

Next steps

Once the students have completed making the rainbow of different colors in the glass they can experiment further by trying to mix the colors together in the glass. They can hypothesis and explore what they think may happen to the liquid once it is mixed together before doing this extra part of the experiment.

Citations and links