Whats the difference between crack and free-base cocaine?

Cocaine: People abuse 2 forms of cocaine: the water-soluble hydrochloride salt that is injected or snorted, and the water-insoluble Cocaine base (or freebase) that is smoked. Free-base Cocaine has been processed with ammonia or baking soda and water, and then heated to remove the hydrochloride. The term “crack, ” is the street name given to freebase Cocaine -- it makes "crackle" sounds when smoked.