How does salt make icy roads safe?
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Mixing salt w/ water lowers its freezing point; adding salt to an icy road will cause the snow/ice to melt and will help prevent snow ice buildup. A wet road is safer than an icy road.
Salt water has a lower freezing the regular water so when the salt and snow/ice mix the it melts.
Salt lowers the freezing point of water so the roads have to get a lot colder for them to become icy. The sodium ions and chloride ions in common salt interrupt the water molecules bonding together to form ice and so lower the freezing point of water. https://youtu.be/oVJAZ002v5k
Technically, it does not make them “safe,” so much as removes a more dangerous condition (ie. Low friction surfaces) from being *as much* of an effect on people’s “normal” driving abilities ***if they must drive*** in those less than ideal conditions.
Chemically, however… Salt generally lowers the freezing temperature of water a significant amount (something like a 5 to 1 “absorption” (not absorption) ratio… Meaning, it’s pretty efficient).
So, if it’s 31F outside, and you apply salt to ice … There’s a pretty good chance that part of the ice will melt. Water is less slippery than ice, so “conditions improve.”
Salt water freezes at a lower temperature than fresh water. 0°F is the freezing point of seawater compared to 32°F for fresh, for instance. While different salinities (ratio of salt to water) can affect the exact temperature, the goal of salting roads is to prevent ice from forming by keeping the freezing point of the water below the ambient temperature.
Salt lowers the freezing point of water. When you spread salt on a road, and cars drive on it, a bit of the ice melts from friction, and salt mixes with that water. That then helps melt more ice, which mixes with salt, until you have mostly salt water instead of ice on the roads.
Usually they don’t use regular salt, they use a mixture of different kinds of salt, like calcium chloride, and some sand, which helps cars get more traction on the ice.
Still, if it gets cold enough, salt doesn’t help much, because even salt water will freeze. In those cases, they usually mix in a lot more sand and tell people to stay off the roads.
In addition to salt’s ability to melt snow and ice, undisolved salt also increases friction on the road surface. Salt chrystals are generally cube shaped so they don’t roll or slip passed each other very easily, snow and ice on the other hand form into little plate shaped chrystals that slide around like playing cards. Sand, ashes, and kitty litter can have the same effect as well, but none of those melt the ice
looks like no one has mentioned it, but salt lowers the freezing point of water, turning the ice into water
Something to help visualize that salt lowers the freezing point of water 😂- the ocean doesn’t freeze unless it’s very very cold
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