- Formula
- Structure
- How is it done?
- Properties
- Physical properties
- Solubility
- Heat of dissolution
- Electrolytic decomposition
- References
The calcium chloride (CaCl 2) is an inorganic salt composed of calcium, alkaline earth metal and halogen chlorine. In this compound there are several electrostatic interactions that define the external appearance of its crystals and the rest of its physical properties.
Likewise, it is always accompanied by water molecules, forming hydrates of general formulas CaCl 2 xH 2 O, with x = 0, 1, 2, 4 and 6. When x = 0, the salt lacks water and is anhydrous, as indicates its chemical formula mentioned above.
Solid portions of CaCl 2 are illustrated in the upper image. In low humidity conditions, it is possible to keep anhydrous salt free of water, although its natural tendency is to absorb it until it dissolves (deliquescence).
Formula
Its chemical formula is CaCl 2: it expresses that for each Ca 2+ ion there are two Cl ions - which neutralize the positive charge. The calcium metal - from group 2 of the periodic table (Mr. Becambara) - gives up its two electrons to each chlorine atom, an element of group 17.
Structure
- Avoid freezing the water during winter. Calcium chloride generates a lot of heat as it dissolves and then, as the temperature increases, the ice melts. For this reason it is used to reduce the risk of the movement of people and vehicles during the cold season.
- Helps control dust on unpaved roads.
- Accelerates the drying speed of concrete once poured.
- CaCl 2 liquids increase the efficiency of drilling for the extraction of gas from its underground deposits, as well as that of oil.
- It is added to pools to reduce the erosion suffered by the concrete of their walls. The sedimented calcium fulfills this function.
- Because it is a hygroscopic salt, calcium chloride can be used as a desiccant, being able to lower the humidity of the air that surrounds it and, therefore, of the substances in contact with that air.
- It is used as a preservative in some foods, as well as an additive in several of these, such as energy drinks used by athletes, cheeses, beers, etc.
- In medical practice it is also useful in the treatment of depression caused by an overdose of magnesium sulfate, as well as in lead poisoning.
How is it done?
The natural sources of this compound are the brines extracted from the seas or lakes.
However, its main source comes from the Solvay process, in which limestone (CaCO 3) undergoes a series of transformations until the by-product is calcium chloride:
2NaCl (aq) + CaCO 3 (s) <=> Na 2 CO 3 (s) + CaCl 2 (aq)
The product of interest from this process is actually sodium carbonate, Na 2 CO 3.
Properties
Physical properties
It is a white, odorless and hygroscopic solid. This tendency to absorb humidity from the environment is due to the basicity of Ca 2+ ions.
Basicity of what kind: Lewis or Bronsted? From Lewis, due to the fact that the positive species is capable of accepting electrons. These electrons are donated, for example, by the oxygen atoms in water molecules.
The solid absorbs moisture to the point of dissolving in the same water that wets its crystals. This property is known as deliquescence.
Its density is 2.15 g / mL. As it incorporates water into its structure, the crystal "expands", increasing its volume and, consequently, decreasing its density. Only CaCl 2 · H 2 O breaks with this trend, showing a higher density (2.24 g / mL).
The molecular weight of the anhydride salt is approximately 111 g / mol, and for each molecule of water in its structure this weight increases by 18 units.
Solubility
CaCl 2 is very soluble in water and in some polar solvents, such as ethanol, acetic acid, methanol, and other alcohols.
Heat of dissolution
When dissolved in water, the process is exothermic and, therefore, heats the solution and its surroundings.
This is due to the fact that the aqueous complex stabilizes the Ca 2+ ions in solution to a better degree than the electrostatic interactions with Cl - ions. Since the product is more stable, the solid releases energy in the form of heat.
Electrolytic decomposition
Molten CaCl 2 can be subjected to electrolysis, a physical process that consists in the separation of a compound into its elements from the action of an electric current. In the case of this salt, the products are metallic calcium and gaseous chlorine:
CaCl 2 (l) → Ca (s) + Cl 2 (g)
Ca 2+ ions are reduced at the cathode, while Cl - ions are oxidized at the anode.
References
- Lisa Williams. (December 20, 2009). Icy Road.. Retrieved on April 9, 2018, from: flickr.com
- Wikipedia. (2018). Calcium chloride. Retrieved on April 9, 2018, from: en.wikipedia.org
- J. Mehl, D. Hicks, C. Toher, O. Levy, RM Hanson, GLW Hart, and S. Curtarolo, The AFLOW Library of Crystallographic Prototypes: Part 1, Comp. Mat. Sci. 136, S1-S828 (2017). (doi = 10.1016 / j.commatsci.2017.01.017)
- Shiver & Atkins. (2008). Inorganic chemistry. In The elements of group 2. (Fourth edition., P. 278). Mc Graw Hill.
- PubChem. (2018). Calcium Chloride. Retrieved on April 9, 2018, from: pubchem.ncbi.nlm.nih.gov.
- OxyChem. Calcium Chloride: A Guide to Physical Properties. Retrieved on April 9, 2018, from: oxy.com
- Carole Ann. Common Uses of Calcium Chloride. Retrieved on April 9, 2018, from: hunker.com