That’s why many cities spray a salt solution before any ice forms. It’s important to note that the salt must be in a solution with liquid water in order for this principle to be obeyed.
The degree of freezing point depression depends on how salty the solution is. The salt impedes the ability of the water molecules to form solid ice crystals. If the water is mixed with salt, though, the freezing temperature of the solution is lower than 32 F. Salt prevents the water molecules from solidifying into ice crystals at 32 F, instead staying slushy at that temperature, before eventually freezing around 15 F. So if there’s snow, sleet or freezing rain and the ground is 32 F or colder, solid ice will form on streets and sidewalks. The freezing point of pure water, the temperature at which it becomes ice, is 32 degrees Fahrenheit. Subjecting the environment to this salt via runoff can have some unintended consequences including negative effects on plants, aquatic animals and wetlands.īut it’s a cheap and effective way to protect roads from ice due to a simple scientific principle: freezing point depression of solutions. Road salt isn’t as pure as what you use on your food it has a brownish gray color, mostly due to mineral contamination. There are some proprietary mixtures that contain other salts-such as potassium chloride (KCl) and magnesium chloride (MgCl)-but they’re not as commonly used.
This salt is very similar to the salt you have on your dinner table-it’s the same sodium chloride, NaCl. They’re working to protect drivers from slippery conditions by spraying rock salt or a solution of salt water to prevent ice formation. We all know why the first two happen-kids are excited for a day off of school filled with hot chocolate and snowmen.
The following essay is reprinted with permission from The Conversation, an online publication covering the latest research.īrrr… it’s cold out there! Children are flocking to the television in hopes of hearing there will be a snow day the bread and milk aisles at grocery stores are empty because of an impending snow storm and utility trucks are out spraying salt or salt water on the roads.
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