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Make Corn Kernels Float-A Kitchen Science Activity


January 26, 2012

Demonstrate buoyancy and chemical reactions

By: Kim McNeill
top image
Kim McNeill

This is a pretty simple science-in-the-kitchen demonstration using items you probably already have, though I may be the only one who still makes popcorn in the microwave with a brown paper lunch bag, so it might be harder to find popcorn kernels. 

Materials (all measurements are rough estimates):

  • A clear, tall container—I used a 1 quart Mason jar
  • 3 cups of water
  • 1/4 to 1/3 cup of baking soda
  • 1/8 cup of unpopped popcorn kernels
  • 1/4 to 1/2 cup of white vinegar

 

Instructions:

  1. Mix baking soda and water in the clear container
  2. Add corn kernels
  3. Pour in vinegar (over or near a sink! It may foam over the top)—it may need a little stir
  4. If you do not have a 1 quart container, try halving the amount of water, baking soda, and vinegar. 

See a video of our results:

Toddlers through middle schoolers will all get something from this experiment. My preschooler was just excited to see something change. I pointed out that there were bubbles on the kernels and that when the kernels reached the surface, those bubbles disappeared and then the kernel started sinking again.

Elementary aged students should explore how the bubbles make the kernels rise. Bubbles float in water and where there are enough bubbles on the kernel, the bubbles natural ability to rise is stronger than the gravity pulling the kernel to the bottom of the jar. They should be able to see quickly that the number of bubbles on the surface of the kernel will determine whether it will rise or fall. Ask them to try to figure out how much of the corn kerenl needs bubbles before it rises.

With middle schoolers you can start with the same talk as with elementary students. Talk about the kernels rising and falling. The bubbles are pushed up by an upward force called bouyancy because they are not as dense as water. Each bubble adds its upward bouyant force to the other bubbles on the kernel.  The kernels will rise when the upward bouyant force of the bubbles is larger than the downward force of gravity.

If your child is very interested, ask why the bubbles might form on the kernel  (Bubbles like to form on tiny, sharper places--nucleation sites.) They can try to estimate how many bubbles it takes to get the kernel to move up. Ask your child where the bubbles are coming from.

Turn it into a science experiment by putting kernels in plain water, water with baking soda, and water with vinegar. Are lots of bubbles forming on the kernels in any of those? What about seltzer water? Carbon dioxide gas dissolves in water. Seltzer water has carbon dioxide dissolved in it. Can they guess where the bubbles come from now? A chemical reaction occurs when baking soda and vinegar are put together; they create carbon dioxide. 

Happy science exploring!


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