The formula for Ferric ferrocyanide, widely recognized as Prussian Blue, is C18Fe7N18.
Understanding Ferrocyanide Terminology
The term "ferrocyanide" specifically refers to the complex anion [Fe(CN)₆]⁴⁻, also systematically known as hexacyanoferrate(II). The "ferro-" prefix within "ferrocyanide" indicates that the iron within this complex anion is in the +2 oxidation state (Fe(II)).
The original question, "ferro ferrocyanide," can be ambiguous due to the repeated "ferro." In chemical nomenclature:
- Ferrous (or ferro) refers to Iron(II) (Fe²⁺) in simple salts.
- Ferric refers to Iron(III) (Fe³⁺) in simple salts.
Given the reference provided, which pertains to "Ferric ferrocyanide," the question is best interpreted as seeking the formula for this specific compound, commonly known as Prussian Blue. However, for clarity, it's worth noting the distinction:
- Ferric Ferrocyanide (Prussian Blue): This compound features an Iron(III) (Fe³⁺) cation bonded to the hexacyanoferrate(II) anion.
- Ferrous Ferrocyanide: A less common or typically less stable compound that would theoretically feature an Iron(II) (Fe²⁺) cation bonded to the hexacyanoferrate(II) anion.
The Chemical Formula of Ferric Ferrocyanide (Prussian Blue)
Based on PubChem data (CID 2724251), the precise chemical formula for Ferric ferrocyanide is C18Fe7N18.
This aggregated molecular formula directly corresponds to the more commonly expressed structural formula of Prussian Blue, which is Fe₄[Fe(CN)₆]₃. Let's break down how these two representations are equivalent:
- The structural formula Fe₄[Fe(CN)₆]₃ indicates that there are four Iron(III) ions (Fe³⁺) acting as cations and three hexacyanoferrate(II) anions ([Fe(CN)₆]⁴⁻).
- Each [Fe(CN)₆]⁴⁻ anion consists of one central Iron(II) ion (Fe²⁺) coordinated with six cyanide ligands (CN⁻).
To derive the aggregated formula C18Fe7N18 from Fe₄[Fe(CN)₆]₃:
- Total Iron (Fe) atoms: 4 (from the Fe³⁺ cations) + 3 (from the Fe²⁺ within the anions) = 7 Fe
- Total Carbon (C) atoms: 3 (anions) × 6 (C per anion) = 18 C
- Total Nitrogen (N) atoms: 3 (anions) × 6 (N per anion) = 18 N
Thus, the formula C18Fe7N18 accurately represents the elemental composition of Ferric ferrocyanide.
| Compound Name | Common Structural Formula | Aggregated Molecular Formula | Cation Iron State | Anion Iron State |
|---|---|---|---|---|
| Ferric Ferrocyanide | Fe₄[Fe(CN)₆]₃ | C18Fe7N18 | Iron(III) (Fe³⁺) | Iron(II) (Fe²⁺) |
| Ferrous Ferrocyanide | Fe₂[Fe(CN)₆] | Fe₃C₆N₆ | Iron(II) (Fe²⁺) | Iron(II) (Fe²⁺) |
Note: While "ferro ferrocyanide" could literally suggest Ferrous Ferrocyanide (Fe₂[Fe(CN)₆]), the context of the provided reference strongly points to Ferric Ferrocyanide, which is a significant and widely studied compound known as Prussian Blue.
Applications and Importance
Ferric ferrocyanide, or Prussian Blue, is renowned for its vibrant, deep blue color and has been used for centuries:
- Pigment: It is a historically significant pigment extensively used in paints, inks, and as a popular artist's color. Its excellent lightfastness and intense hue make it highly valuable.
- Medical Antidote: In medicine, it is used as an oral treatment for thallium poisoning and radioactive cesium contamination. It works by binding these toxic ions in the digestive tract, preventing their absorption and facilitating their excretion.
- Electrochemistry: Its redox properties make it useful in certain electrochemical applications, including electrochromic displays and as a component in some battery technologies.
- Analytical Chemistry: It plays a role in various analytical procedures, such as the qualitative and quantitative detection of iron(II) ions through the formation of Turnbull's blue, which is chemically identical to Prussian blue.
The unique charge-transfer interactions between the iron centers in different oxidation states within its lattice contribute to its characteristic intense blue color.
