Quote:
Originally Posted by MarkB
Rock salt is Sodium Chloride - NaCl. Calcium Chloride is CaCl2. When NaCl dissolves, there are two ions - one of Na and one of Cl. When CaCl2 dissolves, there are three ions, one of Ca and two of Cl. That's why Calcium Chloride works better. Both are chemical reactions - they lower the temperature at which water freezes - so they cause ice to melt as long it the temperature is above the new freezing temp.
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I hate to nitpick, but isn't dissolving a physical change? You mix table salt into water, then evaporate all the water and you'll still have table salt. If it were a chemical reaction, then a new compound would have to be created.
Dissolving salts into water raises the boiling point of water and lowers the freezing point. I believe calcium chloride lowers the freezing point more than NaCl would and is why it is more effective at dealing with ice.
I always loved chemistry in college is high school.