Why Does Salt Melt Ice or Snow?

When you go out to clear an icy walkway, which would you rather do? Scrape the ice off with a shovel, or sprinkle salt on it before you start? Most people find salt makes the job easier.

When you sprinkle salt on ice, it causes little holes and cracks to appear in the ice. That's because of something that happens at a microscopic level.

Ice (like snow) is a bunch of molecules that stick together in an organized pattern called a crystal.

When salt comes into contact with ice, it breaks up the crystal pattern. It attracts some of the water molecules away from other water molecules, and this makes little holes in the ice.

Other substances, such as sand can do this too -- but not as well as salt. Also, putting salt on your walkway is not as environmentally friendly as using other stuff (the salt ends up travelling to fresh water sources).

ACTIVITY
The Amazing Melting Ice Cubes:

You'll need 5 ice cubes, a cookie sheet, a spoonful each of salt, sugar, flour, pepper and Nothing.

WHAT TO DO: Place the ice cubes on the cookie sheet. Sprinkle a spoonful of salt on one, sugar on the next one, flour on the third, and pepper on the fourth one. Put Nothing on the last ice cube. Watch to see what happens to each ice cube as it melts. Which melts fastest? Slowest?

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Chemistry / Physics Links

Chemical of the Week
Kids OLR: links to numerous chemistry sites