Rock Salt by Any Other Name...
Rock salt, known commonly as sodium chloride, is a naturally occurring mineral referred to as halite. Halite is created when saltwater bodies evaporate, such as Salt Lake in Utah. The chemical makeup of rock salt, or NaCl, consists of 39.34% sodium (Na) and 60.66% chloride (Cl).
Melting is Such Sweet Sorrow
Think of rock salt as “Romeo” and your icy patio as the Capulet’s party, in which Romeo Rock Salt shows up uninvited and wreaks havoc on the chemical bond of the ice. Ice is formed when water (H2O) drops below 32 degrees F (zero degrees C). Upon impact with the ice, rock salt immediately begins to fall apart, literally. The sodium molecules separate from the chloride modules, leaving charged ions, which then bond with the water molecules. These busy, charged ions create kinetic energy, or heat, thus raising the temperature of the ice and melting it.
Doubly productive, though, is the “freezing point depression” that occurs, meaning that the introduction of rock salt lowers the necessary temperature to freeze this now saltwater solution. Salt-saturated water freezes at -6 degrees F (-21.1 degrees C), but hopefully your backyard isn’t that cold! Below -6 degrees F, the sodium and chloride molecules separate from the water molecules and form crystals, which is why glaciers are actually made up of fresh water.
Wherefore Art Thou Rock Salt?
Rock salt is the most common material used to melt ice for one simple reason-- it’s inexpensive. Anything that dissolves in water, however, can be used to melt ice, for example sugar, baking soda, or even alcohol. The process of dissolving creates energy, which is heat, therefore raising the temperature of the ice above freezing.
While extremely cost effective, rock salt does have a few drawbacks. If used on icy roads, for instance, it may eat away at the paint on cars. When used at home, pets may eat rock salt, which, although not terribly dangerous, can cause complications after repeated ingestion. Also, rock salt isn’t great for the environment as far as runoff from highways affecting local flora and fauna.
As the temperature outside begins to fall, enjoy those brisk mornings and cozy mittens, but be responsible about your walkways, driveways, and patios by shoveling and salting. It doesn't have to be a chore. As William Shakespeare said, "these violent delights have violent ends," and listening to the ice crackle and snap can be oh so fun!
References
Shakespeare, William. Romeo and Juliet. William Shakespeare: The Complete Works. New York: Random House, 1975. 1025.
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