cobaltchloride

Cobalt(II) chloride is a chemical compound with the formula CoCl₂. It is a salt in which cobalt is in the +2 oxidation state and chloride is the counteranion. In its anhydrous form it appears as a blue-black powder while the hydrated forms, especially the hexahydrate, are red to purple. The color change between anhydrous and hydrated forms is a classic indicator of moisture and is widely used in laboratory demonstrations and as a visual humidity indicator.

Physical and chemical properties include high solubility in water and many organic solvents. When dissolved, the solution is blue due to the Co²⁺ ion in an octahedral environment; upon drying the solution turns deep purple as the CoCl₂·6H₂O crystals form. The compound has a melting point of about 705 °C for the anhydrous salt, while the hexahydrate decomposes around 140 °C. Cobalt(II) chloride acts as a mild oxidizing agent and is used in the preparation of other cobalt complexes and polymers. It is also employed as a catalyst in certain organic reactions, such as the synthesis of vinyl chlorides.

Preparation techniques traditionally involve the direct combination of cobalt metal or cobalt(II) oxides with hydrochloric acid, followed by evaporation of the solution. Industrial production often uses the reaction of cobalt(II) sulfate or cobalt(II) nitrate with dilute hydrochloric acid, precipitating cobalt(II) chloride as a salt that is then crystallized.

Safety considerations note that cobalt(II) chloride is toxic if ingested or inhaled and can irritate skin, eyes, and mucous membranes. It should be handled with gloves and eye protection, and adequate ventilation is recommended. In addition, acute exposure may cause respiratory irritation, and long‑term effects may include skin sensitization. Proper waste disposal procedures must be followed in accordance with local regulations for hazardous materials.