Calcium chloride is commonly encountered as ahydrated solid with generic formulaCaCl2·nH2O, wheren = 0, 1, 2, 4, and 6. These compounds are mainly used for de-icing and dust control. Because theanhydrous salt ishygroscopic and deliquescent, it is used as adesiccant.[10]
Calcium chloride was apparently discovered in the 15th century but wasn't studied properly until the 18th century.[11] It was historically called "fixedsal ammoniac" (Latin:sal ammoniacum fixum[12]) because it was synthesized during the distillation ofammonium chloride with lime and was nonvolatile (while the former appeared tosublime); in more modern times (18th–19th cc.) it was called "muriate of lime" (Latin:murias calcis, calcaria muriatica[12]).[13]
Bydepressing the freezing point of water, calcium chloride is used to prevent ice formation and is used tode-ice. This application consumes the greatest amount of calcium chloride. Calcium chloride is relatively harmless to plants and soil. As a de-icing agent, it is much more effective at lower temperatures thansodium chloride. When distributed for this use, it usually takes the form of small, white spheres a few millimeters in diameter, calledprills. Solutions of calcium chloride can prevent freezing at temperatures as low as −52 °C (−62 °F), making it ideal for filling agricultural implement tires as a liquid ballast, aiding traction in cold climates.[14]
It is also used in domestic and industrial chemical airdehumidifiers.[15]
Calcium chloride was sprayed on this road to preventweathering, giving it a wet appearance even in dry weather.
The second largest application of calcium chloride exploits itshygroscopic nature and the tackiness of its hydrates; calcium chloride is highly hygroscopic and its hydration is anexothermic process. A concentrated solution keeps a liquid layer on the surface ofdirt roads, which suppresses the formation of dust. It keeps the finer dust particles on the road, providing a cushioning layer. If these are allowed to blow away, the large aggregate begins to shift around and the road breaks down. Using calcium chloride reduces the need forgrading by as much as 50% and the need for fill-in materials as much as 80%.[16]
In the food industry, calcium chloride is frequently employed as a firming agent in canned vegetables, particularly for canned tomatoes and cucumber pickles.[17][18][19][20] It is also used in firmingsoybean curds intotofu and in producing acaviar substitute from vegetable or fruit juices.[21][22][23] It is also used to enhance the texture of various other products, such as whole apples, whole hot peppers, whole and sliced strawberries, diced tomatoes, and whole peaches.[24][25]
The firming effect of calcium chloride can be attributed to several mechanisms:[24]
Membrane stabilization, since calcium ions contribute to the stabilization of the cell membrane.[24]
Turgor pressure regulation, since calcium ions influence cellturgor pressure, which is the pressure exerted by the cell contents against the cell wall.[24]
Calcium chloride's freezing-point depression properties are used to slow the freezing of the caramel in caramel-filled chocolate bars.[citation needed] Also, it is frequently added to sliced apples to maintain texture.[26]
Inbrewing beer, calcium chloride is sometimes used to correct mineral deficiencies in the brewing water. It affects flavor and chemical reactions during the brewing process, and can also affect yeast function during fermentation.[27][28][29][30][31]
Incheesemaking, calcium chloride is sometimes added to processed (pasteurized/homogenized) milk to restore the natural balance between calcium and protein incasein. It is added before the coagulant.[32]
The elemental calcium content in calcium chloridehexahydrate (CaCl2·6H2O) is approximately 18.2%. This means that for every gram of calcium chloride hexahydrate, there are about 182 milligrams of elemental calcium.
For anhydrous calcium chloride (CaCl2), the elemental calcium content is almost twice higher, that is around 36.1% (for every gram of anhydrous calcium chloride there are about 361 milligrams of elemental calcium).
Calcium chloride has a very salty taste and can cause mouth and throat irritation at high concentrations, so it is typically not the first choice for long-term oral supplementation (as acalcium supplement).[40][41] Calcium chloride is highly soluble in water – dissociating into calcium and chloride ions when dissolved. These ions are efficiently absorbed from the intestine.[42] The dissolution of calcium chloride in water is exothermic; releasing energy as heat. If undissolved calcium chloride is ingested, this can lead to burns in the mouth, throat,esophagus, and stomach. Ingestion of large amounts of undissolved calcium chloride has been reported to result in burns, and rarely, necrosis of the stomach.[43][44]
The extremelysalty taste of calcium chloride is used to flavorpickles without increasing the food'ssodium content.[45]
Calcium chloride is used to preventcork spot andbitter pit on apples by spraying on the tree during the late growing season.[46]
Drying tubes are frequently packed with calcium chloride.Kelp is dried with calcium chloride for use in producingsodium carbonate. Anhydrous calcium chloride has been approved by the FDA as a packaging aid to ensure dryness (CPG 7117.02).[47]
The hydrated salt can be dried for re-use but will dissolve in its own water of hydration if heated quickly and form a hard amalgamated solid when cooled.
Calcium chloride is a highly soluble calcium salt. Hexahydrate calcium chloride (CaCl2·6H2O) has solubility in water of 811 g/L at 25 °C.[1] Calcium chloride when taken orally completely dissociates into calcium ions (Ca2+) in the gastrointestinal tract, resulting in readily bioavailable calcium. The high concentration of calcium ions facilitates efficient absorption in the small intestine.[42][53] However, the use of calcium chloride as a source of calcium taken orally is less common compared to other calcium salts because of potential adverse effects such as gastrointestinal irritation and discomfort.[53][54][55]
When tasted, calcium chloride exhibits a distinctive bitter flavor alongside its salty taste. The bitterness is attributable to the calcium ions and their interaction with human taste receptors: certain members of theTAS2R family of bitter taste receptors respond to calcium ions; the bitter perception of calcium is thought to be a protective mechanism to avoid ingestion of toxic substances, as many poisonous compounds taste bitter. While chloride ions (Cl−) primarily contribute to saltiness, at higher concentrations, they can enhance the bitter sensation. The combination of calcium and chloride ions intensifies the overall bitterness. At lower concentrations, calcium chloride may taste predominantly salty. The salty taste arises from the electrolyte nature of the compound, similar to sodium chloride (table salt). As the concentration increases, the bitter taste becomes more pronounced: the increased presence of calcium ions enhances the activation of bitterness receptors.[56][57][58]
Calcium chloride is used in concrete mixes toaccelerate the initial setting, but chloride ions lead to corrosion of steelrebar, so it should not be used inreinforced concrete.[59] The anhydrous form of calcium chloride may also be used for this purpose and can provide a measure of the moisture in concrete.[60]
Calcium chloride is included as an additive in plastics and infire extinguishers, inblast furnaces as an additive to control scaffolding (clumping and adhesion of materials that prevent the furnace charge from descending), and infabric softener as a thinner.[citation needed]
Calcium chloride is used as a water hardener in the maintenance ofhot tub water, as insufficiently hard water can lead to corrosion and foaming.[citation needed]
In theoil industry, calcium chloride is used to increase the density of solids-freebrines. It is also used to provide inhibition of swelling clays in the water phase of invertemulsion drilling fluids.[citation needed]
Calcium chloride (CaCl 2) acts asflux material, decreasing the melting point, in the Davy process for the industrial production of sodium metal through theelectrolysis of moltenNaCl.[citation needed]
Calcium chloride is also an ingredient used in ceramicslipware. It suspends clay particles so that they float within the solution, making it easier to use in a variety of slipcasting techniques.[citation needed]
For watering plants to use as a fertilizer, a moderate concentration of calcium chloride is used to avoid potential toxicity: 5 to 10 mM (millimolar) is generally effective and safe for most plants—that is 0.55–1.11 grams (0.019–0.039 oz) of anhydrous calcium chloride (CaCl 2) per liter of water or 1.10–2.19 grams (0.039–0.077 oz) of calcium chloride hexahydrate (CaCl 2·6H 2O) per liter of water.[61][62] Calcium chloride solution is used immediately after preparation to prevent potential alterations in its chemical composition.[63][64] Besides that, calcium chloride is highly hygroscopic, meaning it readily absorbs moisture from the air.[65] If the solution is left standing, it can absorb additional water vapor, leading to dilution and a decrease in the intended concentration.[65] Prolonged standing may lead to the precipitation of calcium hydroxide or other insoluble calcium compounds, reducing the availability of calcium ions in the solution[66] and reducing the effectiveness of the solution as a calcium source for plants.[66] Nutrient solutions can become a medium for microbial growth if stored for extended periods.[67] Microbial contamination may alter the composition of the solution and potentially introduce pathogens to the plants.[67] When dissolved in water, calcium chloride can undergo hydrolysis, especially over time, which can lead to the formation of small amounts of hydrochloric acid and calcium hydroxide:Ca+ 2+2H 2O ⇌Ca(OH) 2+2H+ . This reaction can lower thepH of the solution, making it more acidic.[68] Acidic solutions may harm plant tissues and disrupt nutrient uptake.[citation needed]
Calcium chloride dihydrate (20 percent by weight) dissolved inethanol (95 percent ABV) has been used as asterilant for male animals. The solution is injected into the testes of the animal. Within one month,necrosis of testicular tissue results in sterilization.[69][70][non-primary sources needed]
Cocaine producers inColombia import tons of calcium chloride to recover solvents that are on theINCB Red List and are more tightly controlled.[71]
Although the salt is non-toxic in small quantities when wet, the stronglyhygroscopic properties of non-hydrated calcium chloride present some hazards. It can act as anirritant bydesiccating moist skin. Solid calcium chloride dissolvesexothermically, andburns can result in themouth and esophagus if it is ingested. Ingestion of concentrated solutions or solid products may causegastrointestinal irritation orulceration.[72]
Calcium chloride dissolves in water, producing chloride and theaquo complex[Ca(H2O)6]2+. In this way, these solutions are sources of "free" calcium and free chloride ions. This description is illustrated by the fact that these solutions react withphosphate sources to give a solid precipitate ofcalcium phosphate:
3 CaCl2 + 2 PO3−4 → Ca3(PO4)2 + 6 Cl−
Calcium chloride has a very highenthalpy change of solution, indicated by considerable temperature rise accompanying dissolution of the anhydrous salt in water. This property is the basis for its largest-scale application.
Aqueous solutions of calcium chloride tend to be slightly acidic due to the influence of the chloride ions on the hydrogen ion concentration in water. The slight acidity of calcium chloride solutions is primarily due to the increased ionic strength of the solution, which can influence the activity of hydrogen ions and lower thepH slightly. The pH of calcium chloride in aqueous solution is the following:[74][75]
Structure of the polymeric[Ca(H2O)6]2+ center in crystalline calcium chloride hexahydrate, illustrating the high coordination number typical for calcium complexes.
In much of the world, calcium chloride is derived fromlimestone as a by-product of theSolvay process, which follows the net reaction below:[10]
Calcium chloride occurs as the rareevaporite minerals sinjarite (dihydrate) andantarcticite (hexahydrate).[77][78][79] Another natural hydrate known is ghiaraite – a tetrahydrate.[80][79] The related mineralschlorocalcite (potassium calcium chloride,KCaCl3) andtachyhydrite (calcium magnesium chloride,CaMg2Cl6·12H2O) are also very rare.[81][82][79] The same is true for rorisite, CaClF (calcium chloride fluoride).[83][79]
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