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Ice Cube Towers

Students use changes of state to create chilly architecture and some slippery slopes!

Salt lowers the freezing point of water. As it dissolves, the ice melts around each grain of salt. As a result, the ice is unevenly eaten away, forming a pitted, non-skid surface. This is why salt is used to melt ice on roads and walkways.

The salty water also re-freezes on the surface of the ice cubes, joining them together. This happens because the insides of the ice cubes are much colder than the freezing point of water. They are cold enough to draw heat out of the newly melted water and it re-freezes.

Objectives

  • Investigate the interactions of liquids and solids.

  • Investigate changes of state.

Materials

  • ice cubes
    salt in a salt shaker
    plate or tray to work on (not paper!)

Key Questions

  • Why do the ice cubes stop slipping off when you add salt?

What To Do

  1. Try to stack ice cubes into a tower.
  2. Try again—but this time let the ice cubes sit out on a plate for 2–3 minutes. Then sprinkle lots of salt on the top of each cube before putting the next one on top of it.

Extensions

  • Put a piece of string on an ice cube, then sprinkle it with salt. Wait a few moments, then lift the string. The water should melt then re-freeze, sticking the string to the ice cube.

Other Resources

Science World Resources | Full Unit | Wonderful Water