Why is salt thrown on the frozen road ?

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Why is salt thrown on the frozen road ?..

Answer / guest

One unique propety of water is that its solid form is less
dense than its liquid form. This is why ice floats and
also why lakes don't freeze from the bottom up. In the
liquid form, water molecules at any given moment react with
an average of 3.6 other molecules of water. As liquid
water cools it becomes most dense at 4C. When it reaches
its freezing point at 0C, the molecules arrange themselves
so that they are reacting with exactly 4 other molecules of
water, expansion.
When salt(NaCl) is added to water it separates into Na+ and
Cl- and the water molecules form a hydration shell around
them. Now, when water reaches its freezing point, its
regular ice structure is disrupted by the presense of these
hydration shells around Na+ and Cl-. This effect is best
demonstated by icebergs. The ice forms a jagged structure
mostly underwater. Water normally freezes in sheets.
The salt is not actually lowering waters freezing point,
water is still chemically the same. The salt is just
disrupting ice formation (hypothetical-it will still take
lower temperatures to have noticable ice formation). You
will have better driving conditons when the roads do turn
icy. You won't have a slick layer of ice anymore...for a
period of time at least.