Ferric ferrocyanide has which chemical formula from the following options?

Ferric ferrocyanide has which chemical formula from the following options?

• A. Fe3[Fe(CN)6]2
• B. Fe4[Fe(CN)6]2
• C. Fe4[Fe(CN)6]3
• D. Fe5[Fe(CN)6]3

Answer: (C)

This item tests how oxidation states and charge balance work in a mixed-valence coordination solid. Ferric ferrocyanide contains ferric ions (Fe3+) and ferrocyanide units [Fe(CN)6]4−. If we take four Fe3+ ions, their total positive charge is +12. With three ferrocyanide units, the total negative charge is 3 × (−4) = −12. The charges cancel, giving a neutral compound with the formula Fe4[Fe(CN)6]3, where the lattice iron is Fe3+ and the ferrocyanide units remain [Fe(CN)6]4−. Other options would force the lattice iron to have non-integer oxidation states or break charge balance, which isn’t consistent with ferric ferrocyanide’s composition.

This item tests how oxidation states and charge balance work in a mixed-valence coordination solid. Ferric ferrocyanide contains ferric ions (Fe3+) and ferrocyanide units [Fe(CN)6]4−. If we take four Fe3+ ions, their total positive charge is +12. With three ferrocyanide units, the total negative charge is 3 × (−4) = −12. The charges cancel, giving a neutral compound with the formula Fe4[Fe(CN)6]3, where the lattice iron is Fe3+ and the ferrocyanide units remain [Fe(CN)6]4−.

Other options would force the lattice iron to have non-integer oxidation states or break charge balance, which isn’t consistent with ferric ferrocyanide’s composition.