Question

oxidation state of iron in Fe₄[Fe(CN)₆]₃ is
a)+12/5
b)+10
c)+18/7
d)+1

Answer 1

It is Berlin blue ( Ferric ferrocyanide. Ferric hexacyanoferrate (II)) . Iron can have two oxydation number : +3 and +2.

You can understand that the first iron has the number +three because it needs 3 groups ferrocyanide to make the compound. the groups ferrocyanide have the charge -4, given from 6 ions  

C

N

−

with charge -1 and a atom of iron with charge +2.

So you have some iron with oxydation number + 3 and some with number +2

mathematically you have combining atoms and oxidation numbers:

4 (+3) + 3 [+2 + 6 (-1)] = 0

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