Potassium hexacyanoferrate(II) is added to a solution of CuSO4 and a chocolate-brown precipitate Cu2[Fe(CN)6] forms. The oxidation state of iron in this precipitate is

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Potassium hexacyanoferrate(II) is added to a solution of $CuSO X_{4}$ and a chocolate-brown precipitate $Cu X_{2} [Fe (CN) X_{6}]$ forms. The oxidation state of iron in this precipitate is

The ligand

CN X^{-}

has charge

- 1

, so the complex ion carries charge

x - 6

. Charge balance with two

Cu X^{2 +}

ions (

+ 4

) requires the complex to be

4 -

, so

x - 6 = - 4

and

x = + 2