So it’s -10 °C where I am today and there are loads of puddles on the pavements and roads because they have been salted (I’m aware that the ground temperature might be higher than -10). But I can’t wrap my mind around the fact that above 0 °C salt can be solid but when it’s diluted into water it lowers the freezing temperature.
But to what temperature? Is there a point where salt is no longer effective on roads and pavements?
Does it depend on the amount of salt mixed with water?
When the sea freezes is it only the H2O that solidifies? What about the salt?
Please, this has kept me up at night!
In: Chemistry
> But to what temperature?
If your using plain old rock salt it works up to -21.1C (-6F)
> Is there a point where salt is no longer effective on roads and pavements?
Yes. As you get closer to the temperature above the effectiveness of the salt becomes less.
> Does it depend on the amount of salt mixed with water?
It can (so “yes”?). No one cares about salt being on the road (within reason), but they’re very concerned about ice and snow. So if you have excess salt it’s not a problem. In order to get the maximum possible effect (i.e. to get down to the -6F I mentioned before) you need the mass of salt to be ~37% of the mass of the ice/water. If you have less then the lowest temperature you can have no ice at will be lower.
> When the sea freezes is it only the H2O that solidifies?
For the most part yes, it’s just the water that solidifies. Roads are a little different because there isn’t a big pool of water for the ‘extra’ salt to go into. So if you use salt on the road and it then ends up too cold for the salt to work you end up with a mixture of close to pure ice, and a bunch of ‘wet’ solid salt.
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