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Trioxalatocobaltate II

trioxalatocobaltate iii

Cobalt-60 is used as a radioactive isotope in the Schilling test, to determine whether vitamin B12 is being produced in the body. It is also used in medicine for the treatment of certain cancers, as it gives off radiation which kills the cancer cells.

There are a number of other radioactive isotopes of Cobalt-60 and they are all used for different reasons. Some are used in medicine to treat diseases such as rheumatism, while others are used to make a variety of products such as the common multivitamin pills.

The oxidation state of Cobalt changes from +2 to +3 in the presence of oxygen. This is caused by the pink hexaamminecobalt(II) complex (which is unstable in the presence of oxygen) being oxidised to the brown hexaamminecobalt(III) complex.

This hexaamminecobalt(III) ion is stable in the presence of ammonia. It is formed by a ligand exchange reaction, where 6 ammonia molecules displace the water ligands on the cobalt ion. The octahedral structure of the complexes is made up of six unidentate ligands and has a coordination number of 6 from these.

When hydrochloric acid is added to the solution it turns from a pink to a blue colour. This is caused by the cobalt ion changing from a cation to an anion, because it replaces one of the water molecules with a chloride ion. This is a reversible reaction, and when the solution is re-additive with water it returns to its original pink colour.