Egg Float

by Karin Deboer

How do youy keep an egg from sinking?

 

The purpose of this demonstration is for students to understand some differences between fresh and salt water.

 

I will provide the questioning that I used in class.

Teachers may want to provide some activities for the students to do before this demonstration to increase prior knowledge or as follow-up activities after the demonstration. Some activities would be to do the demonstration with different solutions with different densities. Or put layers of the different solutions in one cup and observe the seperate layers.

 

Here is the demo:

Materials:

  1. fresh egg
  2. large drinking glass or beaker
  3. water
  4. salt
  5. teaspoon

Optional:

  1. small piece of carrot
  2. large piece of carrot

Procedure:

 

  1. Tell students: I'm going to put a raw/fresh egg in some tap water-watchwhat happens. It will sink.
  2. Ask students: What do you think will happen to the egg if I put somesalt in the water?
  3. Take some suggestions. Add salt to water. Add one teaspoon of salt at a time-it may take some time to dissolve (leave the egg in the glass). Ask the students to record how many teaspoons of salt are added to the water. The egg will eventually float. (The reason for recording the number of teaspoons of salt is so that the demo can be redone with other objects such as carrots, etc.). The egg will float.
  4. Ask students: What do you think will happen to the egg if I now add some fresh water?
  5. Take some suggestions. Add fresh water to the salt water. Do it slowly and use a spoon. Use a different spoon than the one that was used to stir the salt water-a clean one. Put the spoon just above the surface of the salt water, flat. Pour the water slowly down the length of the spoon. This will ensure that there is no mixture of the two solutions. The egg should stay where it is, floating on the salt water and sinking in the fresh water (in the middle of the glass or beaker).
  6. Ask the students: "What may be a possible explaination for what the egg did in the two different types of water? Explain or why do you think that?"
  7. If time allows, repeat this demo with other objects such as a piece of carrot.