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A salt crystal

How and why salt melts ice

Ever wonder why people pour salt on icy sidewalks to make the snow melt? Usually the result is a big pile of slush made of melted snow and ice crystals. And why do the lakes and streams freeze over solid while the ocean always remains flowing? Is there something magical about salt? Are there other uses for salt other than flavoring our food and raising our blood pressure? Let’s try this experiment and see for ourselves.

Test #1:

  1. Take 2 cups of water.
  2. Place about a tablespoon of salt in one of the cups.
  3. Place both cups in the freezer.
  4. Check each cup about every 10 minutes. Can you guess which one will freeze first?

 

Test #2:

  1. Now grab a ice cube out of the freezer.
  2. Place the ice cube on a plate and begin sprinkling salt on the ice cube. Melt Down! Now you can understand why people put salt on their icy driveways.

Salt lowers the freezing point of water. Normally, water freezes when the temperature reaches about 32 degrees Fahrenheit (0 degrees Celsius). When you mix salt with water you actually lower this freezing point. Salty water will still freeze but the temperature has to be colder than it would for normal water. How much colder? That depends upon how much salt you put in the water. The more salt you add the colder it must get before the water freezes.

Experiment Supplies

Supplies: Salt

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