![]() This 19-electron species is a good reducing agent, being readily oxidised to the yellow 18-electron cobaltacenium cation, which is isoelectronic with ferrocene. Reaction of anhydrous CoCl 2 with sodium cyclopentadienylide in THF gives the black sandwich compound cobaltocene. ![]() For example, the reaction of 1-norbonyllithium with CoCl 2 produces the brown, thermally stable cobalt(IV) tetralkyl - the only compound of its kind for which the detailed structure is fully known : In the laboratory, cobalt(II) chloride serves as a standard precursor for the synthesis of other cobalt compounds. Otherwise, aqueous solutions of cobalt(II) chlorides behave like other cobalt(II) salts, such as precipitating CoS upon treatment with H 2S. These cobalt (II) complexes are usually either octahedral or tetrahedral. Similarly, paper impregnated with cobalt chloride, known as "cobalt chloride paper" is used to detect the presence of water.ĬoCl 2♶H 2O and CoCl 2 are weak Lewis acids that convert to many other complexes. When cobalt(II) chloride is added as an indicator, the drying agent is blue when still active, pink when exhausted, corresponding to anhydrous and hydrated CoCl 2, respectively. In the US calcium sulfate is sold as a drying agent under the trade name Drierite. The hydrated form can be prepared from cobalt(II) hydroxide or cobalt(II) carbonate and hydrochloric acid.Ī common use for cobalt(II) chloride was for the detection of moisture, for example in drying agents such as silica gel this use was disscontinued due to the carcenogenic nature of cobalt salts. CoCl 2♶H 2O is deliquescent and the anhydrous salt CoCl 2 is hygroscopic, readily converting to the hydrate.Ĭobalt(II) chloride can be prepared in its anhydrous form from cobalt metal and chlorine gas: ![]() It has the interesting property that a concentrated aqueous solution is red at room temperature, but becomes blue when heated. This species dissolves readily in water and alcohol. In the solid state CoCl 2♶H 2O contains trans-♲H 2O, two water molecules in its formula unit being water of crystallization. The rose hexahydrate is one the most common cobalt compounds in the laboratory.Īqueous solutions of both CoCl 2 and the hydrate contain the species 2+. Because of this dramatic color change and the ease of the hydration/dehydration reaction, "cobalt chloride" is used as an indicator for water. CoCl 2 is blue, and CoCl 2♶H 2O is deep rose. Rhodium(III) chloride Iridium(III) chlorideĮxcept where noted otherwise, data are given for materials in their standard state (at 25 ☌, 100 kPa) Infobox disclaimer and referencesĬobalt(II) chloride is the chemical compound with the formula Co Cl 2, although the term is used also to refer to the hexahydrate, which is a different chemical compound. 2 Dangerous for the environment ( N)Ĭobalt(II) fluoride Cobalt(II) bromide Cobalt(II) iodide Cobalt(II) oxide When conducting experiments, wearing gloves can ensure the substance doesn’t transfer to hands.Toxic ( T) Carc. Named for a shade of blue, cobalt chloride in liquid or paper form is toxic when ingested. When heated, wet cobalt chloride paper can turn back from pink to blue as the water molecules are burned off and the original crystalline structure of the chemical is restored. According to the American Chemistry Council, cobalt chloride has a crystalline structure that changes as the molecules shift to make room for water molecules, leading to the color change that makes this substance ideal for detecting the presence of humidity. Cobalt chloride paper can be purchased in premade sheets, but it can also be made by dipping paper into a cobalt chloride solution and letting it dry.Īs humidity increases, cobalt chloride will shift from blue to pink, with a purplish color serving as the mid-phase hue between these two colors. ![]() Cobalt chloride is an inorganic salt that is bright blue when it is not exposed to humidity. When testing for humidity, the experimenter can simply use cobalt chloride paper to detect airborne water particles.
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