The Density of Saltwater

Grade Levels: 3 - 6

Objectives

  • Students will learn that saltwater is denser than freshwater.

Materials

  • One of the following for each student group:
    • A one cup measure
    • A 1/4 cup measure.
    • Eye dropper
    • Two eggs
    • Two clear 16 oz. glasses
  • Water
  • Salt
  • Food coloring

Procedures

  1. Write the following definition of density on the board:
    • Density is the weight of a liquid divided by the space it occupies.
  2. Tell students that the following experiment involves a comparision between the density of fresh water and salt water.
  3. Divide students into small groups and distribute the cup measures, eye dropper, eggs and glasses to them.
  4. Ask the students to fill one of the glasses with 1 cup of water.
  5. Direct the students to gently drop one egg into the water and watch what happens.
  6. Ask students to fill the second glass with 1 cup of water and 1/4 cup of salt.
  7. Tell them to stir until the salt is completely dissolved.
  8. Ask students to add a few drops of food coloring to the salt water and allow it to sit for five minutes.
  9. Direct the students to carefully and slowly add fresh water using the eye dropper, being careful not to disturb the settled colored salt water.
  10. Tell students to drop the second egg into the glass and watch what happens.
  11. Have a class discussion using the following questions:
    • Compare the way the two eggs float. Describe the differences.
    • Why do you think the eggs float differently in the separate glasses?
    • What conclusions can you draw about the density of either the eggs or the water?
  12. After the students have shared their thoughts, explain that the egg sunk in the fresh water because it had greater density than the water in that situation. The egg floated in the salt water because when salt is added to water its density becomes greater than that of the egg. That makes the egg float.
  13. Ask students what implications this might have in the ocean.

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