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
Salt is sodium chloride, NaCl.
When it hits water, those molecules split in half into Na+ and Cl- ions that float around in the water.
When you try to then freeze the water, something interesting happens.
The water molecules want to form up into an orderly hexagonal crystal and make a solid, but there’s a problem: wayward chlorine and sodium ions are haphazardly stuck in the middle and don’t want to leave.
To force them out, you have to suck even more energy out of the system and cool the water further. The more salt you have, the harder it is to freeze the water.
The road salt eventually stops working when you get too cold, even absolute brine water will freeze in intensely cold conditions.
And yes, when sea ice forms most of the salt is expelled.
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