Rainbow Water and Floating Grapes

(A Montessori Science Inspired Experiment)


Take a Guess (Hypothesis)

Which is denser: saltwater or sugar-water? Are either of them more or less dense than regular water?


Part 1

Part 2


Did you guess correctly? Order the 3 liquids from most dense to least dense.

How It Works

Part 1

Grapes are denser than water, so they sink.

Density = Mass / Volume

When you add salt to the water, there are more particles (more matter) in the cup of water. There is more mass, but the volume stays the same.

In other words, when you add salt to water, it increases the density of water. Saltwater is denser than a grape, so it floats.

Sugar-water has more particles in it than plain water. It is denser than plain water. However, sugar-water is still less dense than a grape, so the grape sinks.

Part 2

Both The First Great Lesson and our further work on density showed us that denser particles sink, and less dense particles float.

If you are careful, you can get sugar-water to float on top of saltwater, and plain water to float on top of sugar-water. If you pour too quickly though, all of the particles will mix into one solution. You can try this with Hot and Cold Water too!

Dive Deeper (Do Some Further Research)

What is a solution? How are solutions related to density?

What are some other objects that will sink in plain water, but float in saltwater?

  • Are those objects more or less dense than grapes?
  • Create your own experiment to find out! (Hint: try using different amounts of salt in your solution).