Ever slide through a cold Interstate at night, salt crystals pinging off your side view mirrors, and wonder – just before regaining control – how exactly that salt is supposed to melt ice?
The American Chemical Society has the answer. And it’s chemistry:
When salt (sodium chloride) contacts with water, it dissolves into individual sodium and chloride ions. Those ions wedge their way in between the water molecules, preventing the water from packing into a solid, icy crystal.
So salt doesn’t really melt ice. Instead, it lowers the temperature at which water will freeze. It's a good de-icer down to about 16 degrees Fahrenheit.
Literally any substance dissolved into water will lower the temperature at which it freezes. But according to the American Chemical Society, plain salt is still the best ice buster for the money.
About 20 million pounds of road salt is used each year in the United States. While salt keeps the roads clear, it also corrodes metals and damages the environment.
If you want to get your calculator dirty, you can read the CliffsNotes on freezing point depression.
Gavin Stern is a national digital producer for the Scripps National Desk.