|Other names||cobaltous chloride, cobalt (2+) chloride|
|Molar mass||Molar mass::129.84 g/mol|
|Appearance||Blue crystal or powder in anhydrous form|
|CAS number||CAS number::7646-79-9|
|Density and phase||Density::1.6795 g/ml, solid|
|Solubility in water||
43.6 g/100 mL (0 °C)
|Melting point||Melting point::735°C|
|Boiling point||Boiling point::1,049°C|
|Acidity (pKa)||4.6 in aqueous solution of .2 mol|
|Crystal structure||CdCl2 structure|
|MSDS||Material safety data sheet|
|R/S statement|| R: R49-R22-R43/43-R50/53 |
|Other cations||cobalt (III) chloride|
| Except where noted otherwise, data are given for|
materials in their standard state (at 25 °C, 100 kPa)
Disclaimer and references
Cobalt chloride is an inorganic, crystalline compound that appears as a blue powder. When hydrated, the salt takes on a deep magenta color. This property makes cobalt chloride a very popular moisture indicator in desiccants. Although relatively stable, this compound poses several hazards to the human health, capable of damaging the respiratory and cardiovascular systems. It is also especially dangerous to aquatic environments. Despite these hazards, cobalt chloride is utilized in several ways; besides its presence in desiccants, the cobalt chloride is used as a reagent, in studies of the human body, and as a basis of creating other cobalt compounds.
Cobalt chloride is an inorganic compound that can act as a weakly acidic salt.  One of its most distinct properties is the significant difference in color between the anhydrous (lacking water) and hydrous forms.  The initial appearance of cobalt chloride is a light blue powder, but when hydrated with water molecules, it becomes a deep purple-magenta.  The compound does not have to be submerged in water for this color change to occur--exposure to moist air will turn the blue powder to reddish-pink.  When the moisture is evaporated through heat, the compound will return to its original blue color, demonstrating that the reaction is easily reversible.  Another property of cobalt chloride is its solubility in water, alcohol, acetone, ether, glycerol, and pyridine. The compound is stable alone, but is reactive with alkali metals, certain oxidizing agents, and ammonia vapor. Although it is non-combustible, bead-forms of the compound have been experimented with and are predicted to have a flash point of -10°C.  The compound's smell is also slightly stinging to the nose. As a chloride compound, cobalt chloride can conduct electricity when dissolved or fused in water, and the chlorine gas can be separated from the cobalt metal through electrolysis.  
Depending on the hydrate, cobalt chloride can have a third color. For example, cobalt (II) chloride hexahydrate (CoCl2 . 6 H2O) is the deep magenta color the compound is known for. The dihydrate from (CoCl2 . 2 H2O) is a lighter, more purplish color. Finally, the anhydrous form is blue.  The most common form of cobalt chloride is its hexahydrate form, with a molecular weight of 237.93 g/mol.  It is soluble in the same substances as the anhydrous form, except for pyridine. This crystalline, solid form has an experimental melting point of 87 °C, density of 1.92 g/cm3 at 20 °C, a predicted boiling point of 100°C, and a decomposition temperature of 230 °F. The flash point is not predicted. In contrast to the anhydrous form, the hexahydrate does not have an odor.   
Co(OH)2 + 2 HCl → Co(H2O)6Cl2
As a compound, cobalt chloride is usually available for immediate use in most required volumes.  Cobalt chloride is most significantly known for its use as a choice indicator of moisture in desiccants--substances that will soak up water vapor in the air around them.   In its anhydrous state, cobalt chloride is blue in color. However, when hydrated, it becomes a deep, purplish rose. The stark contrast between the two colors makes it a popular chemical for detecting moisture, as any presence of water will be clearly marked. A common example of this property's application is one of the most widely used desiccant products: Blue Indicating Silica Gel. This gel, in bead form, will turn from blue to pink when fully saturated with moisture. Another way cobalt chloride is used for this specific property is in humidity indicator cards. These cards are pieces of paper injected with the compound, with blue dots that become pink when a certain level of humidity is reached. 
Cobalt chloride is also applied in a variety of other areas. For example, the compound serves as an excellent crystalline, water soluble cobalt source for uses compatible with chlorides.  It can also act as an analytical reagent or, in its hexahydrate form, as a bioreagent, used in dealing with cell structure and insect cell culture.  Because it is an instigator of the production of HIF-1, cobalt chloride is used to study apoptotic effects in HepG2 cells. (HIF-1 is a protein responsible for responding to decreases in oxygen within a cell's environment, and apoptosis is when cells purposely let themselves die). The compound can also be used in studies to examine the protein expression of heat shock in inflamed skin.    In addition, cobalt chloride is utilized as a base for forming other cobalt compounds, which in turn can be found in the following products: alloys, batteries, dyes, pigments, magnets, eye makeup, lotions, glass, tattoos, solid soaps, binding agents in hardening metals, color changing merchandise, and artificial joint replacements.   Because of its color changing characteristic, cobalt chloride has the ability to be used as an invisible ink. When diluted in a solution, the compound is light pink, nearly colorless. If the ink is heated, such as under a light bulb, the salt will dehydrate and turn blue. In a reverse effect, the writing will disappear if it is breathed on, as the moisture emitted returns the compound to its former color. 
As demonstrated by its risk and safety statements, cobalt chloride has several hazards to be cautious of. It is not the most poisonous or deadly chemical, but is still capable of causing harm. Besides the usual protective eyewear and gloves, there are other listed precautions to be aware of. The following are some examples of cobalt chloride's risk and safety phrases.
R Phrases: (22) Harmful if swallowed (42/43) May cause sensitization by inhalation and skin contact (49) May cause cancer by inhalation (50/53) Very toxic to aquatic organisms; may cause long-term adverse effects in the aquatic environment.
S Phrases: (22) Do not breathe dust (53) Avoid exposure--obtain special instructions before use (60) This material and/or its container must be disposed of as hazardous waste.
Due to these characteristics, it is necessary to wear a full-face particle respirator during procedures involving the powdery cobalt chloride.   Different safety label systems, whether they be risk and safety phrases or hazard statements, warn of the potential health hazards that can result from interaction with cobalt chloride, including its hydrated form. The compound causes irritation to the lungs, skin, and eyes, also causing specific harm to the respiratory and cardiovascular systems. Breathing it in can result in asthma, delayed injury, or lung damage, even persistent problems such as pulmonary fibrosis. If it comes into contact with the skin, cobalt chloride may cause and allergic reaction, and prolonged contact may result in dermatitis. Blood abnormalities may also occur if the compound enters the circulatory system, such as thickening of the blood and cardiomyopathy (a chronic heart disease). Ingestion will result in gastrointestinal irritation, including nausea, vomiting, and diarrhea. Thyroid and nerve problems are also possible effects. According to animal studies, cobalt chloride may also be able to cause cancer.  
It is recommended that the compound be protected from moisture, dusty locations, excess heat, and any incompatible materials. Cobalt chloride also has hazardous decomposition products, including hydrogen chloride, irritating toxic fumes and gases, and cobalt and its oxides.  The compound is stable at room temperature in closed containers and under normal conditions, but is incompatible with alkali metals, strong oxidizing agents, and ammonia vapor.  
A video demonstrating cobalt chloride's color change in a chemical reaction.
- Cobalt chloride Cameo Chemicals. Web. Accessed 20 January 2014.
- Cobalt(II) chloride hexahydrate (CAS 7791-13-1) Santa Cruz Biotechnology. Web. Accessed 5 January 2014.
- Cobalt (II) chloride ChemSpider. Web. Accessed 5 January 2014.
- The Chemistry of Cobalt University of North Carolina at Pembroke. Web. Accessed 20 January 2014.
- Cobalt Chloride American Elements. Web. Accessed 5 January 2014.
- Hydrates of Cobalt chloride GenChem. Web. Accessed 20 January 2014.
- Cobalt chloride hexaydrate Sigma-Aldrich. Web. Accessed 5 January 2014.
- Material Safety Data Sheet Iowa State University. Web. 5 January 2014.
- Cobalt chloride Wikipedia. Web. Accessed 21 January 2014.
- What is a Desiccant? USA Emergency Supply. Web. Accessed 7 January 2014.
- Facts: Cobalt Chloride. Web. Accessed 5 January 2014.
- The human side of hypoxia-inducible factor NCBI. Web. Accessed 7 January 2014.
- Apoptosis AudioEnglish.org. Web. Accessed 7 January 2014.
- NA21 Cobalt (II) chloride hexahydrate allergEAZE. Web. Accessed 5 January 2014.
- Making invisible ink The Royal Society of Chemistry. Web. Accessed 5 January 2014.