Is rock salt the same as dry ice?

Rock salt and calcium chloride are not the same thing. Rock salt's molecular formula is the same as table salt, NaCl, Sodium Chloride. It is called rock salt, because it is a mineral salt that forms naturally and is mined. The salt in the sea is dissolved NaCl, the water is then evaporated and sea salt is left behind. Calcium chloride is also a salt, but not one to eat. It has several common applications such as brine for refrigeration plants, ice and dust control on roads, and in concrete. It can be produced directly from limestone, but large amounts are also produced as a by-product of the Solvay process. Because of its hygroscopic nature, it must be kept in tightly-sealed containers.