Cobalt

Today I´m going to talk about cobalt

Cobalt is a brittle, hard, silver-grey transition metal with magnetic properties similar to those of iron (ferromagnetic). Cobalt is present in meteorites. Ore deposits are found in Zaire, Morocco and Canada. The isotope cobalt-60 (⁶⁰Co) is an artificially produced isotope used as a source of γ rays (its high energy radiation is useful for sterilisation in medicine and of foods). Cobalt salts colour glass a beautiful deep blue colour. Cobalt compounds are important catalysts in a number of industrial processes. Cobalt is required in small amounts for life and is the only metal found in vitamins (cobalt is the critical component of vitamin B₁₂.

Table: basic information about and classifications of cobalt.

Name: Cobalt Symbol: Co Atomic number: 27 Atomic weight: 58.933195 (5) Standard state: solid at 298 K CAS Registry ID: 7440-48-4

Group in periodic table: 9 Group name: (none) Period in periodic table: 4 Block in periodic table: d-block Colour: lustrous, metallic, greyish tinge Classification: Metallic

Cobalt: historical information

Cobalt was discovered by Georg Brandt at 1735 in Sweden. Origin of name: from the German word "kobald" meaning "goblin" or evil spirit.

                                    

 

 

 

 

 

 

 

 

 

Minerals containing cobalt were of value to the early civilisations of Egypt and Mesopotamia for colouring glass deep blue.

Cobalt was announced to be an element by Georg Brandt about 1739 (or possibly 1735). He had been trying to demonstrate that the blue colour of glass was because of a new element, cobalt, rather than bismuth, an element often found in the same locations as cobalt.

Cobalt: physical properties

• Melting point: 1768 [or 1495 °C (2723 °F)] K
• Boiling point: 3200 [or 2927 °C (5301 °F)] K
• Density of solid: 8900 kg m^-3

 

Cobalt: orbital properties

• Ground state electron configuration:  [Ar].3d⁷.4s²
• Shell structure:  2.8.15.2
• Term symbol:   ⁴F_9/2
• Pauling electronegativity: 1.88 (Pauling units)
•  First ionisation energy: 760.4 kJ mol^-1
•  Second ionisation energy: 1648 kJ mol^-1

 

Isolation

Isolation: it is not normally necessary to make cobalt in the laboratory as it is available readily commercially. Many ores contain cobalt but not many are of economic importance. These include the sulphides and arsenides linnaeite, Co₃S₄, cobaltite, CoAsS, and smaltite, CoAs₂. Industrially, however, it is normally produced as a byproduct from the produstion of copper, nickel, and lead.

Normally the ore is "roasted" to form a mixture of metals and metal oxides. Treatment with sulphuric acid leaves metallic copper as a residue and disolves out iron, cobalt, and nickel as the sulphates. Iron is obtained by precipitation with lime (CaO) while cobalt is produced as the hydroxide by precipitation with sodium hypochlorite (NaOCl)

2Co²⁺(aq) + NaOCl(aq) + 4OH^-(aq) + H₂O → 2Co(OH)₃(s) + NaCl(aq)

The trihydroxide Co(OH)₃ is heated to form the oxide and then reduced with carbon (as charcoal) to form cobalt metal.

2Co(OH)₃ (heat) → Co₂O₃ + 3H₂O

2Co₂O₃ + 3C → Co + 3CO₂