ROCHESTER, N.Y. (WROC) — Every winter it’s the same song and dance: snow and ice are in the forecast and suddenly a fleet of trucks appears dousing the roads in salt — all in an effort to keep the snow at bay and let daily life try to carry on.
But have you ever asked yourself why is salt so effective against snow and ice? It all has to do with some simple chemistry.
One interesting thing about the reaction that might surprise people is that salt doesn’t exactly melt ice and snow. In reality, it just changes the freezing point of the water, according to Breanna Uckermark, a chemistry teacher with RCSD.
“So normally H2O will freeze at 0 degrees celsius, which is 32 Fahrenheit but when you put road salt into the mixture it won’t freeze [until closer to zero degrees Fahrenheit],” said Uckermark.
This all happens well past the limits of the human eye, and even most microscopes. To be able to see it you’d have to head right down near the atomic level.
“So H2O [water/ice] when it’s a solid, it likes to stay close together it actually forms kind of a hexagon shape…and when the road salt plays in it kind of gets in the way of H2O [water/ice] getting close together so it spreads out the H2O [water/ice] which kind of makes it that liquid,” said Uckermark.
To put it another way: As the salt dissolves on the ice the individual pieces that make up salt, e.g. Sodium and Chlorine [Sodium Chloride], Calcium and Chlorine [Calcium Chloride], etc., get in between the water molecules making it harder for them to connect and form an ice crystal. But there’s also a second process happening too. When salt separates into its two basic halves, they have opposite charges like two halves of a magnet, one is positive and one is negative.
“The concept of opposites attract right? So positives [and] negatives will come together like magnets. The same sort of thing happens with water and table salt where the water is attracted to that table salt because of those charges and sort of pulls away the ions,” said Uckermark.
This helps to keep the water molecules apart and in a sense attached to the dissolved salts, stopping them from freezing, and it also pulls at the ice crystals that are right near the surface of the ice. Slowly but surely that magnetic-like pull begins to weaken the strength of the ice crystal breaking it apart and causing it to switch from a solid [ice], back to plain old water. Which in a broad sense, is melting, but not as you would normally see it if you were to simply apply heat to the ice.