3.5.5 Reactions of Inorganic Compounds in Aqueous Solution - Metal-aqua ions


Students should:
  • know that metal aqua ions are formed in aqueous solution: [M(H2O)6]2+, limited to M = Fe, Co and Cu [M(H2O)6]3+, limited to M = Al, Cr and Fe

Metal salt solutions

In aqueous solution transition metals tend to form octahedral complexes in which the ligands are water molecules. These complexes have six water molecules and are called hexaaqua or hexaaquo complexes.

the hexaaquairon(II) ionthe hexaaquacobalt(III) ion

As transition metals have variable oxidation states, the hexaaqua complexes may be with metals in the 2+ or 3+ oxidation states. However, not all oxidation states are stable in aqueous solution.

Apart from the transition metals, aluminium is also known to form hexaaquaaluminium complex ions:

Hexaaquaaluminium ions