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Ocean Science

Salt Water Density Experiment

You will need:

  • Small plastic jewels or grapes or raisins 
  • Several clear cups full of water
  • Salt
  • Sugar
  • Baking Soda

To extend the experiment you could try other substances like washing powder, coffee, sand etc.

Science is all about experimenting with different substances to see what happens!



  • Dissolve 2 tablespoons of salt in one cup, 2 tablespoons of sugar in another cup, and 2 tablespoons of baking soda in a third cup. One cup needs to be fresh water. This cup is called the control and it is used to make comparisons with the other cups. 
  • What will happen when you drop the jewels into each cup? Male your predictions! Will they sink or float?

The Science behind the Salt Water Experiment

When you add salt to water it makes the water more dense. This means it gets heavier.

Many objects that sink in fresh water will float in salt water!


Objects float in baking soda water because baking soda is a kind of salt.

It dissolves in water to make the water more dense, just like table salt does.

However, baking soda has another property that gave us a little bit of a surprise!


When baking soda dissolves in water some of it reacts to form carbon dioxide gas.

If you look carefully you will see tiny bubbles rising from the bottom of the cup.


Over time the tiny carbon dioxide bubbles attached to the plastic jewels  act like tiny life vests that carry the jewels to the top of the cup.