Calcium chloride
- Calcium chloride
- E 509
- A12AA07
- B05XA07
- G04BA03
Colorless and odorless, hygroscopic crystals
Fixed
- 2.16 g · cm -3 ( anhydrous)
- 1.85 g · cm -3 ( dihydrate)
- 772 ° C ( anhydrous)
- Approximately 176 ° C (dihydrate )
- About 35 ° C ( tetrahydrate)
> 1600 ° C
Well in water (740 g · l-1 at 20 ° C)
Attention
1000 mg · kg -1 ( LD50, rat, oral)
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Calcium chloride (including calcium chloride) is a chloride of alkaline earth metal calcium with the empirical formula CaCl2. Calcium is present here in the 2 oxidation state, chlorine has an oxidation state of -1.
History
By 1860, chemists Robert Bunsen and Augustus Matthiessen succeeded the first purification of the element calcium by melt electrolysis of calcium chloride.
Occurrence
Calcium chloride occurs naturally dissolved in salt brines.
Hydrous calcium chloride forms the rare minerals Sinjarit (dihydrate ) and Antarcticite (hexahydrate ). The anhydride occurs as Hydrophilit.
Production and representation
Calcium chloride is prepared from hydrochloric acid and calcium carbonate:
Subsequent heating at 260 ° C affords the anhydrous form.
Technical calcium chloride is used as a waste product in the production of soda according to the Solvay procedure - receive - and in recovering the ammonia from the ammonium chloride formed thereby:
Properties
Calcium chloride is a salt. Calcium and chlorine are due to the large Elektronegativitätsunterschiedes ago ionic. The bonding is thus carried out by electrostatic interactions. Calcium chloride forms colorless crystals which form a distorted rutile structure.
Calcium chloride forms in pure form colorless crystals and is very hygroscopic in the anhydrous state. It easily takes on water from the environment and forms a hydrate complex.
The anhydrous calcium chloride dissolves exothermically in water.
Reactions
Calcium chloride reacts with water to form a hexahydrate complex and excessive heat ( exothermic, AH < 0):
The crystals of the hexahydrate dissolve at about 30 ° C in its own water of crystallization. Heating to about 200 ° C is the bound water free. Dissolving in water results in contrast to anhydrous calcium chloride to a strong cooling. Both calcium chloride forms are highly soluble in ethanol.
Use
Anhydrous calcium chloride is an important desiccant in the laboratory, for example, in a desiccator, and in industrial chemistry for gases and liquids due to its hygroscopic nature. Applications include the drying of living spaces, the use as antifreeze, in particular as an antifreeze agent and accelerator in concrete, as well as dust binder ( eg, construction sites and as a stocking with blasting operations ).
It is used as a firming agent, flavor enhancer and stabilizer (including in drinking water treatment, surface treatment of fruit). It is approved in the EU as a food additive under the number E 509.
Taking advantage of the exothermic hydration reaction with water in the calcium chloride is used for the heating of finished beverages. Moreover, it comes as road salt and for the production of freezing mixtures used (see above).
Furthermore, it is used for the coagulation of proteins in the food technology and find application in the production of products such as cheese, tofu, or synthetic caviar.
It also serves in molecular biology for the preparation of competent cells. Calcium ion change in this case the permeability of the cell membrane, thus increasing the absorption potential of the cell for DNA.