Cobalt

• COBALT (Co2+/Co3+) is a steel-grey, slightly magnetic metal.
• It melts at 1490°C. The metal dissolves readily in dilute mineral acids
• The dissolution in nitric acid is accompanied with the formation of nitrogen oxide.
• In aqueous solutions cobalt is normally present as the Cobalt (II) ion or Co2+; sometimes, especially in complexes, the cobalt (III) ion or Co3+ is encountered.
• These two ions are derived from the oxides CoO and Co2O3 respectively. The cobalt (II) – cobalt (III) oxide or Co3O4 is also known.
• In aqueous solutions of cobalt (II) compounds the red Co2+ ions are present.
• Anhydrous or undissociated cobalt (II) compounds are blue.
• If the dissociation of cobalt compounds is suppressed, the color of the solution turns gradually to blue.
• Cobalt (III) ions are unstable, but their complexes are stable both in solution and in dry form.
• Cobalt (II) complexes can easily be oxidized to cobalt (III) complexes.