The Science of Modeling the Dead Sea

Whether an object floats or sinks depends on its density—a measure of how much matter is “crammed” into a specific amount of space. If an object is denser than the liquid it is in, it sinks; if it is less dense, it floats.

How Salt Changes Water

A fresh egg is denser than plain tap water, which is why it sinks to the bottom. However, when you dissolve salt into the water, the salt ions fit in between the water molecules. You are adding mass (the salt) without significantly increasing the volume (the space it takes up).

• Increasing Density: As the salinity increases, the water becomes “heavier” for its size.
• The Buoyancy Shift: Eventually, the salt-water solution becomes denser than the egg. At this point, the water provides enough buoyant force to push the egg to the surface.

[Image of an egg floating in salt water vs sinking in fresh water]

Real-World Applications

• The Dead Sea: Located in the Middle East, this sea is nearly ten times saltier than the ocean. It is so dense that humans float effortlessly on the surface without even trying! However, this high salinity makes it a harsh environment; only specialized bacteria called halophiles can survive there.
• Submarine Ballast: Submarines use ballast tanks to control their density. To sink, they fill the tanks with water (increasing mass). To rise, they use compressed air to push the water out, lowering the overall density until it is less than the surrounding sea.

Variables to test

Find out more on variables here.

• Alternative Solutes
  Does this work with sugar instead of salt? Sugar molecules are much larger than salt ions—does it take more or less mass of sugar to make the egg float?
• Object Density
  What other household items can you get to float in your salty solution? Try a grape, a plastic toy, or a piece of pasta. Which requires the highest concentration of salt?
• Thermal Effects
  What happens if the water is warmed or cooled? Temperature changes the volume of water (thermal expansion), which in turn changes its density. Does the egg sink back down if you heat the water?

To keep your experiment valid, make sure you stir the water thoroughly until all the salt is dissolved before checking if the egg floats!