Experiments with Potassium ferrocyanide

 

               Reaction of potassium ferrocyanide with zinc chloride

Potassium hexacyanoferrate (II) is a lemon yellow coloured inorganic complex, also called potassium ferrocyanide. The ferrocyanide ion consists of iron in the +2 state coordinately bonded to six cyano ligands. It is a versatile chemical, and is widely used in qualitative chemical analyses. However, it should not be confused with potassium ferricyanide, which consists of iron in the +3 state coordinately bonded to six cyano ligands, and has reddish crystals.



For this experiment, four solutions were prepared in test tubes. The first was of copper nitrate, the second was of zinc chloride, and the third was of ferrous chloride. The fourth solution was of potassium ferrocyanide in distilled water.

The potassium ferrocyanide solution was added to all the other three test tubes, with visible results.

The three test tubes contain the products of the reaction with potassium ferrocyanide. The brown one is of the reaction with copper nitrate, the bluish white one is of reaction with zinc chloride, and the blue one is of reaction with ferrous chloride.


The brown colour is characteristic of cupric ions, and is used to determine its presence in qualitative inorganic analysis. The bluish white precipitate is characteristic of the reaction between zinc ions and potassium ferrocyanide.

As for the blue one, the colour produced is called Prussian blue, and it is used as a pigment in the paint industry. It is of historic importance, for it has been used since centuries. The colour is produced when potassium ferrocyanide reacts with ferric/ferrous ions.

                              The formation of Prussian blue.



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