Egg Float

It changes its mind.

 

 

 

Category - Solids, Liquids & Gases

Key Idea - Density

 

Purpose - To examine the difference in density between fresh water and salt water

Egg in pure water

 

Egg in salty water

 

 
Nature -  Demonstration
Materials -  beaker, fresh raw egg, distilled water, salt (NaCl), stirring rod
Method - 
  1. Three-quarters fill the beaker with distilled water
  2. Place the egg into the water and note that it sinks
  3. Add salt and gently stir.  Repeat until the egg floats up to the surface.
Safety - Nil
Explanation - The density of fresh water is slightly less than an egg, therefore it sinks.  As you add salt to the water, it becomes more and more dense until it is slightly more dense than the egg, causing the egg to float. 
Notes - This explains why you float better in the sea than you do in a freshwater swimming pool.

Ships that travel through stretches of both fresh and salt water need to be aware of this as they will float lower in the fresh water, perhaps creating a hazard when fully loaded.

Note that this will only work if the egg is fresh.  Eggs that have gone off will float when initially placed in pure water due to the gas that builds up inside the egg.  This would be a pretty cool Science Wizard in itself!