Question

The formula for iron (III) hexacyanoferrate (II), commonly known as prussian blue, is

(a) \(\mathrm{Fe}_{3}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]_{2}\)

(b) \(\mathrm{Fe}_{2}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]_{3}\)

(c) \(\mathrm{Fe}_{4}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]_{3}\)

(d) \(\mathrm{Fe}_{3}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]_{4}\)

Answer 1

Correct option is (c) \(\mathrm{Fe}_{4}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]_{3}\)

We proceed from left to right, iron (III) means Fe³⁺, hexacyano means 6CN^- ions are present and ferrate (II) means Fe²⁺ is the central metal atom.

So, the complex ion is [Fe(CN)₆]^4- and the counter ion is Fe³⁺. So, after balancing the charge, the formula becomes Fe₄[Fe(CN)₆]₃.