Tonight's 'Ask Evan' question comes from William B. William asks, "I know that the roads are always salted when it snows. But, I'm not sure how it works? Can you explain it?
We see those salt trucks out and about both before and during storms that bring snow and ice. The answer is all about science. Essentially salt lowers the freezing or melting point of water. The idea is to take advantage of the lower melting point.
Ice or snow forms when the temperature of water reaches 32 degrees Fahrenheit. When you add salt, that temperature drops. A ten percent salt solution for example freezes at 20 degrees. A 20 percent solution freezes a just 2 degrees. Without getting too detailed, it's all about the speed of molecules and how they come and go within a solid.
So, on a roadway, this means that if you sprinkle salt on the ice you can melt it. The salt dissolves into the liquid water in the ice and lowers its freezing point. If you ever watch salt melting ice, you can see the dissolving process happen. The ice immediately around the grain of salt melts, and the melting spreads out from that point.
If the temperature of the roadway is lower than 15 degrees or so, then the salt really won't have any effect. The solid salt cannot get into the structure of the solid water to start the dissolving process. In that case, spreading sand over the top of the ice to provide traction is a better option.
If you have a question you'd like to ask, send me an email to AskEvan@FOX43.com. Put 'Ask Evan' in the subject line. You can also reach out to me on my Facebook page, Evan Forrester FOX43. Whatever the topic, I'll do my best to get the answers you are looking for.