How Ice Melts - page 2

As some ice successfully freezes out of the salt water, the amount of water compared to salt becomes even less than it was before – lowering the freezing farther.

Eventually the solution will become saturated with salt. The lowest temperature possible for liquid salt solution is -21.1°C. At that temperature, the salt begins to crystallize out of solution not as ice but as  crystals made of two salt molecules bonded to one water molecule (NaCl·2 H2O) until the solution completely freezes. The frozen solution is a mixture of separate NaCl·2H2O crystals and ice crystals like freezing ice cream.

So salt molecules are bonding with water molecules, making it more difficult for ice to form. This is one reason the Ocean doesn’t freeze at the same rate as lakes and ponds. 

It also is the way homemade ice cream is made. Since the ice cream mixture will not freeze at 32°F it can only be frozen by an environment that is lower than 32°F. By mixing salt with ice, due to freezing point depression, a lower temperature is reached which eventually (if you have ever been the crank turner at a family picnic) causes the ice cream mixture to freeze.  You can get the brine temperature down to O°F.

In a traditional home made ice cream maker the salt brine solution absorbs heat from the liquid ice cream mix and gradually lowers the temperature of the mix until it begins to freeze. The ice cream mixture will not begin to freeze until its temperature falls below 27 °F. A ratio of 5 cups of ice to 1 cups of salt should result in a brine temperature around  8° to 12°F which gives significantly rapid cooling in order to make smooth, creamy ice cream.

Other links to pertinent articles:

Highway Deicing and Anti-icing for Safety and Mobility
Why Do They Use Salt to Melt Ice on the Road in the Winter?
But What's going on at the Molecular Level?

Add a new tool to your ice fighting arsenal.