Explore the concept of density in this simple experiment.
Developing SkillsPredicting, observing
What you need
- Transparent container (at least 500 ml)
- One whole uncooked egg
- Spoon for stirring
- 30 ml of salt (2 tablespoons)
- 500 ml of warm water (2 cups)
Ask an adult to help you when working with hot water.
What to do!
- Place the egg in the container.
- Add 500 ml of warm water to the container
- Stir gently and observe the location of the egg in the container.
- Add salt crystals, stir to dissolve and then watch the egg. What do you observe?
The egg rises due to a change in density (mass per unit of volume) of the water. A rock is very dense because of all of the billions of molecules that are packed tightly in a small amount of space. Water is not as dense because its molecules are not packed as tightly – there are fewer molecules in the same amount of space.
The egg is more dense then the water, so it sinks. However, when the salt crystals are added, you are adding more matter (salt molecules) to the water. The salt crystals dissolve and turn the water into a solution that is denser than the egg. This is why the egg floats.
Why does it matter?
The different densities of matter allow materials to be used in different ways. For instance, an anchor is made of dense iron so that it will sink to the bottom of a lake or ocean to hold a boat in place. On the other hand, life jackets are made of materials that are less dense than water and are used to help a person float.
Density is also very important for the proper functioning of the human body. For example, at high altitudes, such as on top of a mountain, it is harder for us to breath because the air is less dense. This means that the air has less molecules per unit of volume and therefore there is less oxygen in each lungful of air. This makes breathing difficult and will make your muscles tired more easily. Some people bring bottled air when climbing very high mountains such as Mount Everest to make sure they are breathing in enough oxygen.
- Does the amount of salt needed to make the egg rise change with the size of the egg?
- What happens if you use cold water instead of warm?
- What happens if you use a hard-boiled egg instead of an uncooked egg?
- Can you make the egg float just above the bottom but not at the surface of the water? If so, how does the amount of salt required to do this compare to the amount needed to get it to float at the surface?
- Do you think it would be easier to float in the ocean or in a swimming pool? Try this out for yourself.