Chemical reactions of the elements

Reaction of cobalt with air

Cobalt is not particularly reactive with air. However on heating the oxide Co3O4 is formed. If the reaction is carried out above 900°C, the result is cobalt(II) oxide, CoO. Cobalt does not react directly with nitrogen, N2.

3Co(s) + 4O2(g) → 2Co3O4(s)

2Co(s) + O2(g) → 2CoO(s)

Reaction of cobalt with water

Water has little effect upon cobalt metal. The reaction between red hot cobalt metal and steam produces cobalt(II) oxide, CoO.

2Co(s) + O2(g) → 2CoO(s)

Reaction of cobalt with the halogens

The dibromide cobalt(II) bromide, CoBr2, is made through the direct reaction between cobalt metal and bromine.

Co(s) + Br2(l) → CoBr2(s) [green]

The corresponding chloride and iodide may be made in the same way, but other methods seem to be used in preference forsynthetic use.

Co(s) + Cl2(g) → CoCl2(s) [blue]

Co(s) + I2(s) → CoI2(s) [blue-black]

Reaction of cobalt with acids

Cobalt metal dissolves slowly in dilute sulphuric acid to form solutions containing the aquated Co(II) ion together with hydrogen gas, H2. In practice, the Co(II) is present as the complex ion [Co(OH2)6]2+.

Co(s) + H2SO4(aq) → Co2+(aq) + SO42-(aq) + H2(g)

Reaction of cobalt with bases

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cobalt atomic number