Calcium chloride

Calcium chloride (CaCl₂) is an ionic 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.

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Chemical properties

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)

Preparation

Uses (industrial)

Millions of tonnes of calcium chloride are made each year in the US alone, and it has a wide variety of industrial applications:

Because it is strongly hygroscopic, air or other gases may be channeled through a column of calcium chloride to remove moisture. In particular, calcium chloride is usually used to pack drying tubes to exclude atmospheric moisture from a reaction set-up while allowing gases to escape. It can also be added to liquids to remove suspended or dissolved water. The dissolving process is highly exothermic and rapidly produces temperatures of around 60°C (140°F). In this capacity, it is known as a drying agent or desiccant. 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

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 (rock salt or halite), it is relatively harmless to plants and soil. It is also more 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, called prills (see picture at top of page).

Used for its hygroscopic property, it can be applied to keep a liquid layer on the surface of the roadway, which holds dust down.^[1] It is used in concrete mixes to help speed up the initial setting, however chloride ion leads to corrosion of steel rebar, so it should not be used in reinforced concrete.^[2]

The aqueous form of calcium chloride is used in genetic transformation of cells by increasing the cell membrane permeability, inducing competence for DNA uptake (allowing DNA fragments to enter the cell more readily). In this form it can lower the freezing point of water as low as -52°C (-62°F), making it ideal for filling agricultural implement tires as a liquid ballast, aiding traction in cold climates.^[3]

It can be used in Medicine to treat Calcium Channel Blocker toxicity with overdoses of drugs such as Diltiazem (Cardizem), to treat certain electrolyte imbalances along with Calcium Gluconate or to help correct hyperkalemia and hypocalcemia. It can also be used to assist treatment of cardiac arrest.

Other industrial applications include use as as an additive in plastics, as a drainage aid for wastewater treatment, as an additive in fire extinguishers, as an additive in control scaffolding in blast furnaces, and as a thinner in fabric softener.

Uses (food)

As an ingredient, it is listed as a permitted food additive in the European Union for use as a sequestrant and firming agent with the E number E509. The anhydrous form has been approved by the FDA as a packaging aid to ensure dryness (CPG 7117.02).^[4]

Calcium chloride is commonly used as an Electrolyte and has an extremely salty taste, as found in sports drinks and other beverages such as Smartwater and Nestle bottled water. It can also be used as a preservative to maintain firmness in canned vegetables or in higher concentrations in pickles to give a salty taste while not increasing the food's sodium content. It is even found in snack foods, including Cadbury Caramilk chocolate bars (purpose unknown).

Other than as a preservative, it can be used to make ersatz caviar from vegetable or fruit juices^[5] or added to processed milk to restore the natural balance between calcium and protein for the purposes of making cheese such as brie and stilton. Calcium chloride's exothermic properties are exploited in many 'self heating' food products where it is activated (mixed) with water to start the heating process, providing a non-explosive, dry fuel that is easily activated.

Precautions

Calcium chloride is an irritant, particularly on moist skin. Wear gloves and goggles or a full face shield to protect hands and eyes; avoid inhalation.

Dry calcium chloride reacts exothermically when exposed to water. Burns can result in the mouth and esophagus if humans or other animals ingest dry calcium chloride pellets. Small children are more susceptible than adults (who generally have had experience trying to eat hot food, and can react accordingly) so calcium chloride pellets should be kept out of their reach.

References

1. ^ Dust: Don't Eat It! Control It!. Road Management & Engineering Journal. US Roads (TranSafety Inc.) (1 June 1998). Retrieved on 9 August, 2006.
2. ^ Accelerating Concrete Set Time (1 June 1999). Retrieved on January 16, 2007.
3. ^ Agricultural Tire Hydroinflation. www.firestoneag.com. Firestone Tires (December 2007). Retrieved on 3 December, 2007.
4. ^ CPG 7117.02. FDA Compliance Articles. US Food and Drug Administration (March 1995). Retrieved on 3 December, 2007.
5. ^ Apple Caviar Technique. StarChefs Studio. StarChefs.com (April 2004). Retrieved on 9 August, 2006.

General references

• Greenwood, N. N.; Earnshaw, A. (1997). Chemistry of the Elements, 2nd Edition, Oxford:Butterworth-Heinemann. ISBN 0-7506-3365-4. 
• Handbook of Chemistry and Physics, 71st edition, CRC Press, Ann Arbor, Michigan, 1990.