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Reactions of Cobalt
Reactions with water
Water has little or no effect on cobalt. However, the reaction of red-hot cobalt and steam produces cobalt(II) oxide.
  2Co(s) + O2(g)2CoO(s)
Reactions with air
Cobalt is not very reactive with air. Cobalt will not react directly with nitrogen. Heating will produce cobalt oxide.
  3Co(s) + 4O2(g)2Co3O4(s)
Heating above 900°C will result in cobalt(II) oxide being formed.
  2Co(s) + O2(g)2CoO(s)
Reactions with halogens
Cobalt reacts with chlorine, bromine and iodine to form cobalt dihalides.
  Co(s) + Cl2(g)CoCl2(s)
  Co(s) + Br2(l)CoBr2(s)
  Co(s) + I2(s)CoI2(s)
Reactions with acids
Cobalt metal dissolves in dilute sulphuric acid to form solutions containing the Co(II) ion and hydrogen gas.
  Co(s) + H2SO4(aq)Co2+(aq) + SO42-(aq) + H2(g)
 
Reduction Potentials
Balanced half-reaction E0 / V
Co3+ + e-Co2+ +1.808
Co2+ + 2e-Co(s) -0.277
Co3O4(s) + 8H+ + 2e-3Co2+ + 4H2O +2.11
Co2O3(s) + 6H+ + 2e- 2Co2+ + 3H2O +1.75
Co(OH)2(s) + 2e-Co(s) + 2OH- -0.73
Co(NH3)63+ + e-Co(NH3)62+ +0.1
CoO(OH)(s) + H2O + e-Co(OH)2(s) + OH- +0.17