While refilling my Dry-Z-Air containers, I read the labels on the bags. ‘Contains calcium chloride’. Obviously it is a salt made from calcium and chlorine. But how does it work? I looked it up on Wikipedia and discovered that it is hygroscopic and exothermic. The article also said that it is used for melting ice.
So if I bought an ice-melting product meant for de-icing walkways from the hardware store, is it the same as the packets used in Dry-Z-Air, and could I buy the larger containers to refill them and save money by buying ‘in bulk’? And if I get ice on my walk, can I use the Dry-Z-Air packets to melt it?
The hygroscopic effects of crystals of CaCl are not unlimited. One has to have it in a very dry state when it is first introduced into the environment to be kept dry. After it is exposed to humidity for some time (a few days in an open environment, many months in a sealed container) it no longer has the capacity to absorb moisture. Any salt will melt ice, some more efficaciously than others. Tearing open a few thousand small packets might be considered a drawback by some users.
Calcium chloride, like many salts, can add water to the crystal as water of hydration. Sometimes even color changes can result, such as with cobalt chloride, which is blue when anhydrous and pink when hydrated (up to 6 water molecules.) That’s how the stuff works as a drying agent (though it’s not my first choice in most cases.) For melting ice, that’s caused by both the exothermic reaction and the solute effect causing freezing point depression.
I have no idea what’s in a bag of de-icing salt. Calcium chloride would be an obvious choice if the manufacturer was going for something less toxic to the environment than sodium chloride. Several dessicants can be used to dry gases, though I don’t know if any of them can be easily picked up in such a way.
