Production
Prussian blue is produced by oxidation of ferrous ferrocyanide salts. These white solids have the formula M2Fe where M+ = Na+ or K+. The iron in this material is all ferrous, hence the absence of deep color associated with the mixed valency. Oxidation of this white solid with hydrogen peroxide or sodium chlorate produces ferricyanide and affords Prussian Blue.
A "soluble" form of PB, K, which is really colloidal, can be made from potassium ferrocyanide and iron(III):
- K+ + Fe3+ + 4- → KFeIII
The similar reaction of potassium ferricyanide and iron(II) results in the same colloidal solution, because 3- is converted into ferrocyanide.
"Insoluble" Prussian blue is produced if in the reactions above an excess of Fe3+ or Fe2+, respectively, is added. In the first case:
- 4Fe3+ + 34- → FeIII3
Read more about this topic: Prussian Blue
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