Why Does Salt Melt Ice?

Have you ever lived in or visited a snowy place in the winter? Have you ever wondered why salt is spread over the roads after it snows or why people sprinkle salt over their stairs and walkway when they get icy? Wonder no more because we are going to answer those very questions right now. We are going to bring winter science inside of our kitchen to do an experiment the kids will love.

When salt is mixed with ice it lowers the freezing point. Usually water freezes at 32° F (0° C), but when it is mixed with salt it lowers the freezing point significantly. This simply means the ice melts. We have used this same trick to make yummy treats like fruity ice slush and easy homemade ice cream!

For our experiment today we will use this phenomenon to do a little trick I like to call “Fishing for Ice”.

Total Time: Less than 5 minutes
Safety Concerns: None. All ingredients are safe and edible, though perhaps not very tasty when mixed together!

Materials You Need:
Cup full of water
A few ice cubes
Table salt
A piece of string

Directions:

• Place the ice cubes in the cup of water. They will float on top.
• Try to “fish” for an ice cube with the string. It won’t “catch” anything.
• Place the string in the water and across the top of the ice cubes. 
• Now sprinkle a little bit of salt across the ice cubes. Wait for a minute or so.
• Pull the string out and see what you caught!

Print These Instructions

When salt is sprinkled over ice it melts. However, when it is used in such a small amount, like in our experiment, the water around the ice freezes again quickly. This means that the string gets trapped as the water around it refreezes, thus making it stick to the ice. We were able to freeze all of our ice cubes to one piece of string. How about you?

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Saturday Science

And now on to our Saturday Science linky party! Check out our wonderful co-hosts and link up your own math and science activities:

Popsicle Stick Catapults STEM Activity from Little Bins for Little Hands
Leaf Number Hunt and Match from Stir the Wonder
20 Must-Try Winter Science Experiments from Lemon Lime Adventures
Sledding With Newton’s Laws from Suzy Homeschooler