Calcium chloride is a chemical compound of calcium and chlorine. It is highly soluble in water and it is deliquescent. It is a salt that is solid at room temperature, and it behaves as a typical ionic halide. It has several common applications such as brine for refrigeration plants, ice and dust control on roads, and in cement. 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.
Calcium chloride can serve as a source of calcium ions in solution, for instance for precipitation because many calcium compounds are insoluble:
3 CaCl2(aq) + 2 K3PO4 (aq) → Ca3(PO4)2(s) + 6 KCl(aq)
Molten CaCl2 can be electrolysed to give calcium metal:
CaCl2(l) → Ca(s) + Cl2(g)
Calcium chloride is a by-product of the Solvay process used for the manufacture of sodium carbonate. It can also be produced by the action of hydrochloric acid on calcium carbonate
CaCO3(s) + 2 HCl → CaCl2(aq) + H2O(l) + CO2(g)
Millions of tonnes of calcium chloride are produced in the US alone, and in 1990 its bulk price there was $182 per tonne. It has a variety of applications:
- Because it is strongly hygroscopic, it can be used to dry air as well as other gases and organic liquids. In the process, it is converted to a brine as it absorbs the water or water vapor from the substance to be dried:
- CaCl2 + 2 H2O → CaCl2·2H2O
- The dissolving process is highly exothermic and rapidly produces temperatures of around 60°C (140°F). This can result in burns if humans or animals eat dry calcium chloride pellets. Small children are more susceptible to burns than adults, and calcium chloride pellets should be kept out out their reach.
- Aided by the intense heat evolved during its dissolution, calcium chloride is also used as an ice-melting compound. Unlike the more-common sodium chloride salt (rock salt or halite), it is relatively harmless to plants and soil. It is also effective at lower temperatures than sodium chloride. When distributed for this use, it usually takes the form of small white balls a few millimetres in diameter (see picture at top of page).
- It is used in concrete mixes to help speed up the initial setting and to strengthen the concrete.
- It is used for dust control on some highways, as its hygroscopic nature keeps a liquid layer on the surface of the roadway, which holds dust down.
- Calcium chloride tastes extremely salty and is used an ingredient in some foods, especially pickles, to give a salty taste while not increasing the food's sodium content.
Irritant. Wear gloves and goggles.
- N. N. Greenwood, A. Earnshaw, Chemistry of the Elements, 2nd ed., Butterworth-Heinemann, Oxford, UK, 1997.
- Handbook of Chemistry and Physics, 71st edition, CRC Press, Ann Arbor, Michigan, 1990.