Question

Calculate the oxidation number of the central metal atom (underlined) in the following complex species:

K₄[Fe(CN)₆]

Answer 1

Given complex: K₄[Fe(CN)₆]

Let the oxidation number of Fe be x.

CN⁻ (cyanide ion) has a charge of –1 each.

There are 6 CN⁻ ions, so total charge from ligands = 6 × (–1) = –6.

Potassium ions (K⁺) each have a charge of +1, and there are 4 K⁺ ions, so total positive charge from potassium = +4.

Since the compound is neutral overall:

4(+1) + [x + 6(−1)] = 0

4 + (x − 6) = 0

x − 2 = 0

x = +2

The oxidation number of Fe is +2.