The chemistry of rock salt on a wintry day
Kim Chaudoin | 615.966.6494 |
One of the staple items for winter weather preparedness is salt. NaCl or sodium chloride as it is known to chemists. Technically speaking, the variety on the shelves of most hardware stores is a form of NaCl commonly known as rock salt — or halite — that is formed from sodium chloride.
With the onslaught of winter weather in the Nashville area in recent days and wind chills dipping below zero, local transportation authorities have faced challenges finding solutions for clearing roadways. They often use a liquid slurry of rock salt and calcium chloride (CaCl2) that, in combination with snow plowing, prevents ice formation on roadways if the temperatures are higher than single digit temperatures.
Brian Cavitt, associate professor of chemistry in Lipscomb’s College of Liberal Arts & Sciences, said salt does not work as well in the extreme cold the mid-state has experienced this week. But he says it can work to stop the formation of ice.
In a recent interview with Nashville’s WZTV-FOX 17, Cavitt explained how he teaches his students about the use of salt on roads.
“The ice crystals form like a brick wall,” Cavitt said. “Each water molecule is a brick. Those bricks can form a brick wall easily if you don’t have anything else in the presence of the brick but if you put a bowling ball in the presence of those bricks, they have to migrate around the bowling ball and it takes more effort for ice crystals to form.”
Cavitt said that, interestingly, rock salt is also commonly used to make homemade ice cream, and calcium chloride is used as a preservative and desiccant for food products.
He also explained the slush that forms.
“The slush that you find on the road is the smaller batches of ice from the interruption,” Cavitt said. “The salt crystals getting in the way of the ice itself.”
Temperatures are forecasted to hit the mid-50s in the Nashville area by the weekend, causing any remaining snow and ice to melt .
Lipscomb offers six undergraduate degrees in biochemistry and chemistry. Its professional chemistry major is approved by the American Chemical Society Committee on Professional Training.
Want to know more? Visit chemistry.lipscomb.edu.