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Weather Academy: Let’s make frost!

Published: Dec. 13, 2021 at 5:54 AM CST
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MONROE, La. (KNOE) - Last week on the Weather Academy, we went over frost formation. This week, we will be conducting an experiment that will allow us to see frost forming up close and hopefully give us a better understanding of why frost forms. So let’s dive in!

What you’ll need

  • Two metal cans with labels peeled off
  • Salt
  • Crushed ice
  • Water
  • A spoon

Steps:

  1. Take one of the cans and fill it halfway full with ice. Mix in about four tablespoons of salt.
  2. Take the other can and fill it halfway full of ice. Fill the can with enough water so that the ice is covered.
  3. Let both cans sit for about 30 seconds.
  4. Compare the two cans!

A layer of frost has formed on the outside of Sheena’s can. This is due to the ice and salt mixture. On the other can, liquid moisture condenses on the outside of the can. Why is this happening? The salt wants to absorb water to make a salt solution. To do that, the salt has to melt the ice into water. The heat required to melt the ice comes from the ice itself. The strange effect is caused by the chemical reaction between the salt and the ice. Odd as it seems, melting the ice actually makes the mixture cooler. The saltwater mixture inside the can gets below freezing, so the moisture from the air that collects on the outside of the can will freeze. This is why frost forms! On the other can, dew forms because the mixture of the melting ice and water is just at freezing and the temperature outside the can is warmer, causing water vapor in the air to condense and form dew.

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