Cobalt: the essentials
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.
- Name: cobalt
- Symbol: Co
- Atomic number: 27
- Relative atomic mass (Ar): 58.933195 (5)
- Standard state: solid at 298 K
- Colour: lustrous, metallic, greyish tinge
- Classification: Metallic
- Group in periodic table: 9
- Group name: (none)
- Period in periodic table: 4
- Block in periodic table: d-block
- Electron shell structure: 2.8.15.2
- CAS Registry ID: 7440-48-4
Marmite, which we eat here in England and love it or hate it is a source of vitamin B12, actually a cobalt complex. The equivalent, but blander, in Australia is Vegemite. Marmite is available in the USA. Try mixing it with peanut butter.
Cobalt: historical information
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 around us Read more »
Cobalt salts in small amounts are essential to many life forms, including humans. It is at the core of a vitamin called vitamin-B12. Grazing animals do not to do well in areas where there is little cobalt in the soil.
Cobalt is not found as the free metal. There are a number of important ores from Canada, Morocco, and Zaire. Meteorites often contain cobalt.
| Location | ppb by weight | ppb by atoms | Links |
|---|---|---|---|
| Universe | 3000 | 60 | 
|
| Crustal rocks | 30000 | 10000 | 
|
| Human | 20 ppb by weight | 2 atoms relative to C = 1000000 | 
|
Physical properties Read more »
Density of solid: 8900 kg m-3
Molar volume: |196| cm3
Thermal conductivity: |206| W m‑1 K‑1
Heat properties Read more »
Melting point: 1768 [1495 °C (2723 °F)] K
Boiling point: 3200 [2927 °C (5301 °F)] K
Enthalpy of fusion: |203| kJ mol-1
Crystal structure Read more »
The solid state structure of cobalt is: hcp (hexagonal close-packed).
Cobalt: orbital properties Read more »
Cobalt atoms have 27 electrons and the shell structure is 2.8.15.2. The ground state electronic configuration of neutral Cobalt is [Ar].3d7.4s2 and the term symbol of Cobalt is 4F9/2.
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
Cobalt isotopes Read more »
Naturally occurring cobalt consists of a single stable isotope: 59Co. Cobalt-59 has spin 7/2. The usual NMR reference is K3[Co(CN)6] in D2O. Cobalt-60 is an artifical isotope, and is an important γ-ray source.
| Isotope | Mass /Da |
Natural abund. (atom %) |
Nuclear spin (I) |
Nuclear magnetic moment (μ/μN) |
|---|---|---|---|---|
| 59Co | 58.9331976 (16) | 100 | 7/2 | 4.627 |
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