Chemical elements
  Cobalt
    Isotopes
    Energy
    Production
    Preparation
    Application
    Physical Properties
    Chemical Properties
    Compounds
      Cobaltous Fluoride
      Hydrated Cobaltous Fluoride
      Cobaltic Fluoride
      Cobaltous Chloride
      Cobaltic Chloride
      Cobaltous Bromide
      Cobaltous Iodide
      Cobalt Oxy-fluoride
      Cobalt Oxy-chloride
      Cobalt Chlorate
      Cobalt Perchlorate
      Cobalt Bromate
      Cobalt Iodate
      Cobalt Monoxide
      Cobaltous Hydroxide
      Tri-cobalt Tetroxide
      Cobalt Sesquioxide
      Hydrated Cobaltic Oxide
      Cobalt Dioxide
      Cobalt Monosulphide
      Tricobalt Tetrasulphide
      Cobalt Sesquisulphide
      Cobalt Disulphide
      Cobalt Polysulphides
      Cobaltous Sulphite
      Cobaltic Sulphite
      Cobalt Thiosulphate
      Cobalt Dithionate
      Cobalt Sulphate
      Ammonium Cobalt Sulphate
      Potassium Cobalt Sulphate
      Cobaltic Sulphate
      Ammonium Cobalt Alum
      Potassium Cobalt Alum
      Cobalt Subselenide
      Cobalt Selenide
      Tricobalt Tetraselenide
      Cobalt Sesquiselenide
      Cobalt Diselenide
      Cobalt Selenite
      Cobalt Diselenite
      Cobalt Triselenite
      Cobaltous Selenate
      Cobaltic Selenate
      Cobalt Sesquitelluride
      Cobalt Tellurite
      Cobalt Chromate
      Cobalt Dichromate
      Double Chromates
      Cobalt Molybdate
      Cobalt Nitride
      Cobalt Azoimide
      Nitro-cobalt
      Potassium Cobaltous Nitrite
      Potassium Cobalti-nitrite
      Sodium Cobalti-nitrite
      Sodium Potassium Cobalti-nitrite
      Ammonium Cobalti-nitrite
      Barium Cobalti-nitrite
      Red Sodium Cobalti-nitrite
      Red Barium Cobalti-nitrite
      Red Strontium Cobalti-nitrite
      Zinc Cobalti-tri-nitrite
      Silver Cobalti-tri-nitrite
      Cobalto-cobalti-tri-nitrite
      Cobaltous Nitrate
      Cobaltic Nitrate
      Cobalt Subphosphide
      Cobalt Sesquiphosphide
      Tri-cobalt Diphosphide
      Tetra-cobalt Triphosphide
      Cobalt Hypophosphite
      Cobalt Phosphite
      Cobalt Metaphosphate
      Tri-cobalt Di-arsenide
      Cobalt Monarsenide
      Cobalt Tri-arsenide
      Cobalt Arsenites
      Cobalt Arsenates
      Cobalt Antimonide
      Cobalt Di-antimonide
      Cobalt Antimonate
      Cobalt Thio-antimonite
      Cobalt Carbide
      Cobalt Tetra-carbonyl
      Cobaltous Carbonate
      Basic Cobaltous Carbonates
      Cobaltic Carbonate
      Cobaltous Cyanide
      Potassium Cobalto-cyanide
      Nickel Cobalto-cyanide
      Cobaltous Cobalto-cyanide
      Zinc Cobalto-cyanide
      Cobalti-cyanic Acid
      Ammonium Cobalti-cyanide
      Barium Cobalti-cyanide
      Potassium Cobalti-cyanide
      Cobalt Cobalti-cyanide
      Cupric Cobalti-cyanide
      Ferrous Cobalti-cyanide
      Nickel Cobalti-cyanide
      Silver Cobalti-cyanide
      Lead Cobalti-cyanide
      Sodium Cobalti-cyanide
      Cobalt Thiocyanate
      Cobalt Subsilicide
      Cobalt Monosilicide
      Cobalt Disilicide
      Cobalt Orthosilicate
      Cobalt Fluosilicate
    PDB 1a0c-1epy
    PDB 1et4-1k7y
    PDB 1k98-1r6x
    PDB 1r8k-1v9b
    PDB 1vl3-212d
    PDB 222d-2eff
    PDB 2ehd-2j3z
    PDB 2j4j-2r1p
    PDB 2r2s-331d
    PDB 362d-3fqw
    PDB 3ft6-3igy
    PDB 3igz-3o0n
    PDB 3o0o-4req
    PDB 4xim-9icb

Cobaltous Chloride, CoCl2






Cobaltous Chloride, CoCl2, results in the anhydrous condition when metallic cobalt or its sulphide is heated in chlorine; by heating the hydrated salt to 140° C., or by calcination of the chloropentammine chloride, [CoCl.5NH3]Cl2, in either case in a current of hydrogen chloride; by distilling a solution of the hexahydrated chloride in anhydrous ethylene glycol under reduced pressure; and finally by treatment of a solution of the hydrated chloride with gaseous hydrogen chloride. By the first of these methods blue crystalline scales are obtained which admit of purification by sublimation in a current of chlorine or carbon dioxide. Density, 2.937.

At red heat moist hydrogen reduces it to metallic cobalt. Dry hydrogen acts less readily, and a portion of the chloride sublimes. Magnesium likewise reduces it at high temperatures. The salt dissolves in alcohol to a blue solution, which becomes violet and later rose-coloured upon addition of water. Upon exposure to moist air, the anhydrous salt takes up water, forming first the di-hydrate and then the tetrahydrate.

Aqueous solutions of cobalt chloride may be obtained by dissolving the anhydrous salt in water, or the oxides or carbonate in hydrochloric acid. Upon concentration in the warm the hexahydrate, CoCl2.6H2O, is obtained as dark red monoclinic prisms of density 1.84. These melt at 60° C. in their own water of crystallisation. They lose four molecules of water either when warmed to 50° C. over sulphuric acid, or when kept for a prolonged period in vacuo over the same, the resulting dihydrate, CoCl2.2H2O, being rose-coloured. The dihydrate is also obtained by precipitation from solution on addition of concentrated hydrochloric acid.

By raising the temperature to 100° C. one further molecule of water is expelled, a violet monohydrate, CoCl2.H2O, remaining. The mono-hydrate may also be prepared by concentrating a solution of the hexahydrate in absolute alcohol at 95° C. The salt crystallises out in pale violet needles. At 110° to 120° C. the anhydrous salt is obtained as a blue mass.

The tetrahydrate, CoCl2.4H2O, is obtained by allowing either the anhydrous salt or the dihydrate to remain exposed to moist air. Further exposure yields the hexahydrate.

The solubility of cobalt chloride in water is as follows

Temperature ° C.- 4+ 71112253441454956789496112
Grams of CoCl2 per 100 grams solution28.031.231.332.534.437.539.841.746.748.448.850.551.252.3


..
. cobalt chloride solubility.
. The solubility curves of cobalt chloride.
In the cold the saturated solution is rose-coloured, like the crystalline hexahydrated salt. On warming it becomes violet between 25° and 50° C., above which latter temperature it is blue. This is explained by some as due to a change in hydration of the cobalt salt in solution from the red hexahydrate, through the violet monohydrate, to the blue anhydrous salt. Certainly the changes in colour correspond to breaks in the solubility curve as shown in Fig. A similar change in colour from red to blue likewise occurs with increase of concentration of the solution.

This simple hydration theory cannot explain all the known phenomena, as, for example, the opposite effects of calcium chloride and zinc chloride on the colours. Engel therefore assumed that the observed colours were due to certain double salts present in the solutions. In the case of pure cobalt chloride, hydrolysis was supposed to occur on heating the solution, the hydrochloric acid liberated uniting with unchanged cobalt chloride; and as an explanation of the colour change this is almost certainly incorrect. Ostwald suggested a simple ionic explanation, namely, that the red colour is that of the cobalt cation, and the blue that of the undissociated salt. This is certainly not a complete explanation, and seems to necessitate a very marked decrease in ionisation with rise of temperature, which experiment, so far, does not support.

Donnan and Bassett suggest that cobalt chloride solution, in addition to simple ions Co•• and Cl', contains complex anions CoCl3' or CoCl4', there being two equilibrium reactions in solution, as follow:
  1. CoCl2Co•• + 2Cl'
  2. CoCl2 + 2Cl' ⇔ CoCl4'
    CoCl2 + Cl' ⇔ CoCl3'
Granting that the cobalt ion in solution is red, and that the complete anion is blue and increases in concentration with rise of temperature, the observed colour changes are readily explained qualitatively; for the complex ions will break down with dilution, and also if there be added the chloride of a metal with a greater tendency to form complex ions, e.g. zinc chloride, while the formation of the complex ions CoCl4" (or CoCl3') will be augmented by increasing the concentration of chlorine ions, i.e. by adding hydrochloric acid or the highly dissociated chloride of a metal like calcium, which has little or no tendency to form complex ions. Donnan and Bassett found by electrolytic experiments that the blue solutions contain a blue anion and the red solutions a red cation, and further supported their view by other physico-chemical data; Denham has furnished additional corroborative evidence. Donnan and Bassett conclude that when the cobalt atom is in close association with chlorine, e.g. in CoCl2 and CoCl3' or CeCl4', a blue colour is developed, but that when, by dissociation or the presence of water molecules this close association is broken, e.g. in Co•• and CoCl2.6H2O, a red colour is observed.

The work of Vaillant and Lewis has shown that the colour changes cannot be quantitatively interpreted without considering that water plays a definite role in the reactions. It follows that if Donnan and Bassett's views on complex ion formation be correct, water is either produced or used up when cobalt chloride and chloride ion interact; thus, for example, where the ion CoCl3' is assumed for simplicity:

CoCl2.nH2O + Cl'.mH2OCoCl3'.pH2O + (n + m - p)H2O.

Kotschubei has determined the extent of the hydration of the cobalt ion in cobalt chloride solution by the electrolytic method briefly indicated in the first volume of this Series, and finds that the hydration increases with the dilution. He concludes from his own and other workers' experiments that the hydration diminishes with rise of temperature; also that the hydration of the cobalt chloride molecule varies in the same manner as that of the cobalt ion. He doubts the existence of complex ions in solutions of cobalt chloride, and considers that in the blue solutions formed by the addition of hydrochloric acid, calcium chloride, etc., the evidence for the existence of complex ions is inconclusive. On the other hand, he admits the presence of complex ion in the red solutions containing mercuric chloride, etc., and formulates the ions as probably being:

, , etc.

Cobalt chloride dissolves in alcohol to a blue solution, which becomes violet and then red on the addition of water. The alcoholic solution becomes red when very diluted or when cooled much below 0° C. The blue colour in these solutions has been attributed to the formation of double compound by Engel, to complex ion formation by Donnan and Bassett, and to both these causes by Kotschubei.

The change in colour undergone by cobalt chloride on varying the temperature is taken advantage of in the preparation of sympathetic inks.

The molecular weight of cobalt chloride as determined by the freezing-point method, with urethane as solvent, corresponds to the double formula, Co2Cl4 (compare ferrous chloride), but the results obtained by the boiling-point method indicate that under those conditions the molecule is single, namely, CoCl2.

The hexammoniate, CoCl2.6NH3, is produced by passing ammonia into a concentrated aqueous solution of cobalt chloride in the entire absence of air, or by passing it into a saturated solution of cobalt chloride in methyl acetate. It yields dark rose-red octahedral crystals.


Double Salts of Cobaltous Chloride

An unstable acid chloride, CoCl2.HCl.3H2O, is obtained as blue crystals by cooling to -23° C. a saturated solution of cobalt chloride in aqueous hydrogen chloride. CoCl2.LiCl.3H2O and CoCl2.NH4Cl.6H2O have also been obtained. A blue alcoholate, CoCl2.2CH3OH, is known. With iodine trichloride the complex, CoCl2.2ICl3.8H2O, is formed as orange-red crystals.
© Copyright 2008-2012 by atomistry.com