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Complex Ions

A complex ion is an ion that contains a metal cation bound to one or more small molecules or ions called ligands (such as NH3 or OH-). Complex ions are different to the other compounds you have come across so far. While in a complex ion, a cation is attached to an anion (or another ligand like ammonia) the complex ion has an overall charge to it.

Complex ions are soluble in water, that is, they do not precipitate. You will notice the formation of a complex ion when a precipitate disolves, or a coloured solution is formed. At level two you will come across seven complex ions.
These are:

Al3+(aq) + 4OH-(aq) —> [Al(OH)4]-(aq)

Zn2+(aq) + 4OH-(aq) —> [Zn(OH)4]2-(aq)

Zinc Tetraamine:
Zn2+(aq) + 4NH3 (aq) —> [Zn(NH3)4]2+(aq)

Pb2+(aq) + 4OH-(aq) —> [Pb(OH)4]2-(aq)

Iron III Thyocyanate:
Fe3+(aq) + SCN-(aq) —> [FeSCN]2+(aq)

Copper Tetraamine:
Cul2+(aq) + 4NH3 (aq) —> [Cu(NH3)4]2+(aq)

Silver Diamine
Ag+(aq) + 2NH3 (aq) —> [Ag(NH3)2]+(aq)
At level two you are not required to name complex ions.

Copyright © 2006, 2007 Craig Pilott