Answer: Fe = +2 (CN- is -1 each; 6(-1) + Fe = -4; Fe = +2).
- A Fe = +2 (CN- is -1 each; 6(-1) + Fe = -4; Fe = +2)
- B Fe = +3, the oxidation state found instead in the ferricyanide ion
- C Fe = 0, the oxidation state found instead in neutral iron carbonyls
- D Fe = +4, an oxidation state not consistent with this complex's overall charge
Correct answer: A. Fe = +2 (CN- is -1 each; 6(-1) + Fe = -4; Fe = +2)
Explanation: In [Fe(CN)₆]⁴⁻: each CN⁻ has a charge of -1; 6 CN⁻ contribute -6. Overall charge = -4. So Fe + (-6) = -4; Fe = +2. Ferrocyanide contains Fe(II).
Electron transfer in a redox reaction: zinc loses electrons (oxidised, acts as reducing agent) and copper(II) ions gain those same electrons (reduced, acts as oxidising agent).
Concept context
Master electron transfer in chemistry: assign oxidation states, balance half-reactions, identify oxidising and reducing agents, and connect redox to everyday reactions.