You may have noticed that roads are salted before heavy snowfall during the winter months. More than 20 million tons of salt are used each year to melt snow and ice in cold northern regions. But how does salt do this? In this article, we will explore why salt is sprinkled on roads in the winter and how salt melts ice.
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Why Are Roads Salted When It Snows? How Does Salt Melt Ice?
If you're wondering why roads are salted in winter, first, we need to examine the formation of ice during snowy and cold weather. 32 degrees Fahrenheit (0 degrees Celsius) is the freBezing point; meaning, water turns into ice at 32 °F (0 °C). In this scenario, the road typically has a thin layer of water on top of the ice, and water molecules interact with ice molecules. While water constantly melts some of the ice, the ice underneath refreezes some of the water.
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At this temperature, the amount of water and ice remains the same. If the air gets colder, more water turns into ice. If it warms up, more ice turns into water. When salt is added to the equation, the freezing point of water decreases, which means that the water layer on the ground can no longer freeze at 32 °F (0 °C). Thus, water can melt the ice, resulting in less ice formation on the roads. This also explains why salt is spread on roads.
But you might ask, how does salt melt ice, or how does salt lower the freezing point of water? This concept is called "freezing point depression." Essentially, salt makes it harder for water molecules to bond to each other in their rigid structures. Salt dissolves in water and separates into its elements.
Therefore, if you're using table salt, also known as sodium chloride (NaCl), to melt ice, the salt will dissolve into separate sodium ions and chloride ions.
However, cities often use another type of salt called calcium chloride (CaCl2) on icy streets. Calcium chloride is more effective at melting ice because it can dissociate into three ions instead of two: one calcium ion and two chloride ions. More ions mean more ions can penetrate into the solid ice bonds.
Some other compounds that can melt ice and snow do not contain chloride, but they are much more expensive than sodium chloride or calcium chloride.
In this article, we've discussed why salt is sprinkled on roads when it snows and how salt melts ice. If you have any additional insights or contributions on this topic, feel free to share them with us in the comments below.