Chemical elements
  Cobalt
    Isotopes
    Energy
    Production
    Preparation
    Application
    Physical Properties
    Chemical Properties
      Hydrogen Occlusion
      Detection
      Estimation
    Compounds
    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

Detection of Cobalt





Dry Tests for Cobalt Detection

Salts of cobalt are usually of a rose-red colour when hydrated, and yield a beautiful blue colour in the borax bead test provided they are not present in excessive amount, otherwise the bead becomes opaque and appears black. When heated on charcoal with reduction mixture in the blowpipe test, metallic cobalt separates out in the form of small magnetic beads. When strongly heated with alumina a blue colour is produced, known as Thenard's blue.


Wet Tests for Cobalt Detection

In qualitative analysis by Wet Methods, it is usual to precipitate cobalt, along with any nickel, zinc, and manganese that may be present, by passage of hydrogen sulphide through an ammoniacal solution containing these metals in the presence of ammonium chloride. The sulphides are dissolved in aqua regia, and excess of acid boiled off. Sodium hydroxide or peroxide is now added, whereby the hydroxides of cobalt, nickel, and manganese are precipitated, the zinc remaining in solution. The washed precipitates are dissolved in hydrochloric acid, excess of ammonium acetate added, and the sulphides of cobalt and nickel precipitated with hydrogen sulphide, manganese remaining in solution. It now remains to separate the nickel from the cobalt. This may be effected by Liebig's Cyanide Process, which consists in dissolving the precipitates in aqua regia or hydrochloric acid with a little bromine, boiling off excess of acid or bromine, nearly neutralising with sodium carbonate, and adding potassium cyanide until the precipitated cyanides are just redissolved. After again boiling, which converts the cobalt into potassium cobalti-cyanide, K3CoC6N6, sodium hypobromite is added, which precipitates black hydrated nickel oxide, leaving the cobalt in solution. The solution may now be evaporated to dryness with dilute sulphuric acid, and either tested for cobalt by the dry methods mentioned above, or the presence of cobalt confirmed by any of the reactions:
  1. α-nitroso β-naphthol yields a red precipitate of cobalti-nitroso β-naphthol with acetic acid solutions of cobalt salts.
  2. Potassium thiocyanate yields a blue colour with solutions of cobalt salts, a blue alcoholic layer being produced on addition of amyl alcohol or of alcohol and ether to the mixture and shaking.
  3. Potassium nitrite yields a yellow precipitate of potassium cobalti-nitrite, K3Co(NO2)6, when added to a solution of a cobalt salt containing free acetic acid.
  4. Ammonium sulphide yields a black precipitate when added to an ammoniacal solution of a cobalt salt.
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