Salt and Ice

Lakes and rivers of fresh water begin to freeze at 0° Celsius. But the sea doesn’t. Sea water, which has a salt content of 4%, only begins to freeze at about -2°.

That’s one reason why, in icy winter conditions, people often spread salt on the roads. That salt is generally mixed with brine so it doesn’t blow away as easily in the wind. The salt causes the freezing point of water to drop to about -20° Celsius, which in turn significantly reduces the risk of accidents in winter. However, if too much salt is spread, it can also harm nature, with the salt water flowing into the surrounding soil. Trees such as limes, spruce and maple are especially sensitive to high concentrations of salt. When it comes to pets, salt may cause inflammation of their paws. Also, metal parts of vehicles tend to rust faster.

What will melt first?

You will need

  • 2 ice cubes
  • 2 plates
  • salt


  • Place an ice cube on each plate. Scatter some salt on one, then observe how long it takes for each of the ice cubes to melt.