Known by the chemical formula CaCl2, calcium chloride is an ionic compound of calcium and chlorine. It has no odor and is a solid white crystalline salt at room temperature. It is also called anhydrous calcium chloride or calcium dichloride. It is produced naturally in small amounts from the evaporation of natural brines, as well as by reacting calcium hydroxide with ammonium chloride in Solvay soda ash production and by reacting magnesium hydroxide with sodium hydroxide. It can also be made synthetically. Because it is hygroscopic and deliquescent, it can absorb moisture from the air and help keep food dry, making it ideal for packing. It is also used to prevent ice formation in deicing and as a water treatment agent.

Calcium chloride solutions have high densities, which are beneficial in oil and gas drilling. To make a solution, wear gloves and place limestones in a beaker until it is filled to a fourth of its capacity. Add HCl (hydrochloric acid) to the beaker and gently mix the contents. As soon as the reaction stops bubbling, filter off the particles by pouring the solution through a piece of filter paper. This will leave a second beaker containing solid calcium chloride, which should be warmed.

When it is mixed with water, calcium chloride forms a crystal that tastes very salty. It is often added to sports drinks to replace electrolytes lost during exercise and in cooking as a firming agent. It is also used in medical care to treat low calcium levels, such as tetany. Its irritant properties and exothermic reaction when it mixes with water make it dangerous to handle. Large amounts can cause burning of the mouth or esophagus.