Frozen Cup Rivalry

It has been an unusual winter season for us here in Texas.  We have now officially had 3 Houston snow events and well, that’s unheard of! I’m not so sure it doesn’t have something to do with the incredible hurricane event we had here last summer.

We decided to do a bit of science on this white stuff that we never see when school was closed. (Oh, it turns out that snow is actually not white… go figure!) Little did I know that doing this experiment was going to turn into a sibling rivalry with whose cup will freeze first.

What you need: two plastic or paper cups, water, salt

What you do: 

  • Fill both cups with plain tap water
  • Stir in a tablespoon of salt in one cup
  • Place outside for a few hours in below 32°F weather (or place in a freezer)
  • Guess which one will freeze first

Here are our results. The red cup is plain water. The orange cup is salt water:

What is the science?

Salt lowers the freezing point of the water that it is mixed in. So if it takes water to freeze at 32°F and below then salt water takes much colder temperatures than that to freeze. This is why the ocean doesn’t completely freeze and also why we add salt on bridges and overpasses to help prevent ice from forming.

Andrew was most upset that his orange cup didn’t “win” the frozen contest. I thought he would think his cup was the most interesting. Turns out he didn’t think it was so cool…. (get it!? cool…but I digress.)

We hope you enjoy this easy winter activity!

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