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Which one freezes first? {A Winter Chemistry Activity}

January 15, 2016 2 min read

Winter is a great time to explore the principles of chemistry through experimentation!

This simple experiment will help your students to see how salt changes the freezing point of water.

Let's dig in...

Which one freezes first? {A Winter Chemistry Activity}

Learn about freezing points and chemistry as you do this super fun winter science activity!

In this activity, your students will learn about the freezing point of water and how it can be affected. 

For this demonstration,  you will need 3 cups, water, food coloring, and salt.  You will also need an instant-read thermometer if you have older students. (NOTE: The meat thermometer from your kitchen can work well for this.)

Steps to Complete

  1. Begin by adding one cup of water to each of the cups.
  2. Label each of them with #1 to #3.
  3. Add several drops of food coloring to cup #2 and mix well.
  4. Add 3 TBSP of salt to cup #3 and stir until completely dissolved.
  5. Place each of the cups in the freezer.
  6. Check the cups every 30 minutes for 3 hours to observe what is happening.

NOTE: If your students are older, have them measure and record the temperature of the 3 cups initially and each time they check the cups.

Results

The students should see that cup #1 and cup #2 freeze at the same time, while cup #3 to quite a bit longer to freeze. In fact, they may see that cup #3 does not even freeze in the allotted 3 hours.  

If the students measured the temperatures of each cup, they should see that all 3 cups were around the same temperature each time.

Explanation

Salt lowers the freezing point of water.  This means that water with salt in it will remain a liquid for longer than plain water because the point at which salt water will freeze is lower than 32oF.

Food coloring has no effect on the freezing temperature of water, so it will freeze at the same temperature as the plain water.

Taking it further

Once all of your cups have frozen, have the students take them out of the freezer and see which one melts the quickest.  You can do this by setting each cup on the counter or by heating them in a pan. 

The students should see that cup #3 (the one with the salt) melts quicker, for the same reasons in the explanation. This is why we use salt to melt ice on the driveway during the winter.

Need a few more chemistry activities?

We trust that this activity will serve to make chemistry loads of fun in your homeschool. But we also know that it never hurts to have a few more ideas in your homeschooling bag-o-tricks!

For more ideas, check out one of our chemistry postsprograms or our Chemistry Pinterest Board below!

Follow Elemental Science 's board Chemistry Science Projects on Pinterest.

Did you try this science activity? Let us know how it went in the comments below!



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