Create a colorful rainbow inside a straw while learning a lesson in density. This easy kitchen science experiment uses materials found in your house and can be done by kids of all ages (with a little parental assistance).

Materials

  • Salt
  • Water
  • Measuring spoons
  • Food coloring or Fizzers
  • Clear drinking straw
  • Cups (> 9 oz)
  • Deeper containers like like Baby Soda Bottles (optional)

Experiment

  1. Get your hands on six cups. They don’t have to be the same size, and they don’t need to be clear, but having clear cups of the same size will help add to the experience.
  2. In each of the six cups, add one of six different amounts of salt.
    • 1 tsp
    • 2 tsp
    • 3 tsp
    • 4 tsp
    • 5 tsp
    • 6 tsp
  3. With the salt in each cup, add 9 oz of warm water. Stir the solution until all of the salt has dissolved.
  4. Using food coloring or our non-staining Fizzers, dye the solutions in each cup a different color.
  5. If you would like, you can transfer the solutions to a deeper container, like our Baby Soda Bottles. This will give you a bit more room to create your Salt Water Density Straw.
  6. Grab a clear drinking straw and, if you haven’t already, remove it from its wrapper. (VERY important).
  7. Hold the straw near one end, wrapping your four fingers around the straw and placing your thumb over the straw’s opening.
  8. With your thumb off of the straw’s opening, dunk the opposite end of the straw into the 1 tsp saltwater solution. Cap the straw with your thumb and remove the straw from the solution.
  9. Now that you have the first solution in the straw, dip the end of the straw into the 2 tsp saltwater solution. Dip the straw further, this time, than you did into the first solution. Once you’ve dipped the straw, remove your thumb and quickly replace it. Remove the straw and you should have the first and second solutions in a stack inside of the straw.
  10. Continue the dipping process until you have all six solutions inside of the straw. It’s a density column of salt water!

What will happen if you use sugar? Baking soda? Kool-Aid? Mix up this experiment and test out some additional materials.

FUN FACT: This dramatic salt water density change can be experienced in real life. While humans will (sort of) float in the oceans of the world, we really float in lakes like Utah’s Great Salt Lake and the Dead Sea in Israel and the West Bank.

For the science behind the Salt Water Density Straw, please visit the experiment page.

 

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