Chemical elements
    Physical Properties
    Chemical Properties
      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
      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
      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

Potassium Cobalti-cyanide, K3Co(CN)6

Gmelin first prepared and and described Potassium Cobalti-cyanide, K3Co(CN)6. It is readily produced by the oxidation of the cobalto-cyanide by warming its solution in the presence of air. This reaction is interesting, for when the solution is rapidly oxidised by atmospheric oxygen, twice as much oxygen is absorbed as corresponds to the equation:

2K4Co(CN)6 + H2O + О = 2K3Co(CN)6 + 2KOH, the excess of oxygen remaining, at the close of the reaction, as hydrogen peroxide.

If, however, the oxidation is allowed to proceed slowly, only a slight excess of oxygen is absorbed, and the amount of hydrogen peroxide resulting is proportionately low.

This is readily explained on the assumption that the reaction proceeds in two stages, in accordance with the theory of Engler, namely:
  1. Direct oxidation of the cobalto-cyanide with a molecule of oxygen according to the scheme:
    2K4Co(CN)6 + 2H2O + O2 = 2K3Co(CN)6 + 2KOH + H2O2.
  2. Indirect oxidation of the cobalto-cyanide with the hydrogen peroxide; thus:
    2K4Co(CN)6 + H2O2 = 2K3Co(CN)6 + 2KOH.
In the first case of rapid oxidation by atmospheric oxygen, the indirect reaction has little time to make itself felt. By slow atmospheric oxidation, however, the indirect reaction has a pronounced effect.

On boiling a solution of potassium cobalto-cyanide, hydrogen is evolved in amount equivalent to the oxygen required for the slow oxidation.

Potassium cobalti-cyanide may also be produced by the addition of dilute acetic acid or hydrogen chloride to a solution of the cobalto-cyanide in excess of potassium cyanide. The acid liberates hydrocyanic acid, which reacts as follows:

2K4Co(CN)6 + 2HCN = 2K3Co(CN)6 + 2KCN + H2.

Upon evaporation the salt may be obtained in yellow, anhydrous crystals isomorphous with potassium ferricyanide. Density 1.906.

Finally, potassium cobalti-cyanide results when Fischer's salt (potassium cobalti-nitrite) is added in small portions to a warm, concentrated solution of potassium cyanide. Nitrogen or nitrous oxide is evolved and the solution becomes yellow. On cooling, the potassium cobalti-cyanide crystallises out in pale yellow needles.

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