Give the reaction for the two given: Zn^2+ + K_3Fe(CN)_6 ---> ? and Zn^2+ + K_4Fe(CN)_6 ---> ?
Reaction of potassium ferrocyanide and Zn2+ ions in acid solution is not exactly stoichiometric, and best represented by the following equation,
3Zn2+ + 2 K4Fe(CN)6 = K2Zn3 [Fe(CN)6]2 (s)
A variation of ±3% in Zn2+ concentration values is common, though. In any case, the result is a gray white precipitate of the mixed ferrocyanide complex.
Potassium ferricyanide, on the other hand, is primarily an oxidising agent and does not react with Zn2+ ions, either in cold or hot solution. This inactivity forms the basis of spot identification of Gr.IIIB cations (Mn, Co, Ni, Zn) in a mixture.