Detailed Explanation of K₃[Fe(CN)₆] Structure and Reactions
Potassium ferricyanide is described as a coordination compound having the chemical formula as K3[Fe(CN)6]. This chemical compound is available as a bright red salt under standard conditions for both temperature and pressure (in general, abbreviated to STP). Every potassium ferricyanide molecule holds three positively charged potassium cations and one ferricyanide anion. It is also noted that the ferricyanide anion’s coordination structure is octahedral.
Potassium ferricyanide is much known to be soluble in water. Moreover, this coordination compound’s aqueous water solutions are also known to show specific greenish-yellow or green fluorescence levels. This coordination compound discovery is credited to the German chemist named Leopold Gmelin. Potassium ferricyanide is also believed to have been discovered in 1822. Initially, the main application of this compound was in the dye industry to prepare ultramarine dyes.
Preparation of Potassium Ferricyanide
Potassium ferricyanide is prepared on an industrial scale by obtaining a potassium ferrocyanide solution and passing the chlorine gas through it. When the chlorine gas is passed via potassium ferrocyanide solution, it forms red-coloured potassium ferricyanide. From the potassium ferrocyanide solution, this compound goes on to self separation. The chemical equation for the reaction can be given as follows:
2K4[Fe(CN)6] + Cl2 → 2KCl + K3[Fe(CN)6]
Thus, it is understood that potassium chloride’s two molar equivalents are obtained for every molar equivalent of chlorine gas passed via potassium ferrocyanide solution.
Structure of Potassium Ferricyanide
Potassium ferricyanide is well known to have an extremely complicated polymeric structure (usually with the case of most metal cyanides). A simplified structure of potassium ferricyanide molecules can be given as follows:
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It is important to note that ferricyanide anion, at times known as hexacyanoferrate (III) anion, may contain octahedral coordination geometry. Moreover, the ferricyanide centres in this coordination compound are known to be cross-linked with the potassium cations of positively charged. Also, in this coordination compound, the potassium cations are known to be bound to the cyanide ligands.
It should also make a note that when potassium ferricyanide is dissolved in water, the bond between the cyanide ligand and potassium cation is broken. It is also noted that in the ferricyanide anion, the cyanide group acts as a ligand by donating an electron pair to the central metal atom (in this case, it is iron).
Properties of Potassium Ferricyanide
Some of the important physical and chemical properties of potassium ferricyanide can be listed as follows:
The chemical formula of potassium ferricyanide is given as K3[Fe(CN)6].
This coordination compound’s molar mass is equal to 329.24 grams per mole.
Under any standard conditions, for both temperature and pressure (usually abbreviated as STP), potassium ferricyanide is known to exist in deep red crystal form.
For this coordination compound, it is not uncommon to exist in the form of either pellet or in a powder that is either orange or dark red.
Roughly, the density of this coordination compound is near to 1.89 grams per cubic centimetre under the standard conditions (when it exists in solid phase).
The melting point of potassium ferricyanide is near 573 Kelvin. Thus, this compound melts at a temperature of 300℃.
The potassium ferricyanide compound does not contain any boiling point because it undergoes decomposition prior to reaching any specific boiling point.
Potassium ferricyanide is also known to be highly soluble in water. For suppose, the solubility of this compound in cold water is given as roughly 330 grams per litre.
At a temperature of 20℃, the solubility of potassium ferricyanide in water is given as approximately equal to 464 grams per litre. So, finally, the solubility of this compound in hot water is as high as 775 grams per litre.
It should also be noted that potassium ferricyanide is less soluble in alcohol and is also soluble in specific acids.
This coordination compound’s crystal structure is known to be monoclinic.
Uses of Potassium Ferricyanide
A few of the important applications of potassium ferricyanide are listed as follows:
The most notable application of potassium ferricyanide is in the Cyanotype process, where it is employed in the processes of printing that yield cyan-blue prints.
Also, this compound is known to have several applications in the photography field. For suppose, many processes of print toning in the photography field are known to employ potassium ferricyanide.
Potassium ferricyanide is also employed as an oxidizing agent for the silver removal from certain colour positives and colour negatives.
Also, this compound can be used during iron and steel hardening.
The electroplating process is often done with the help of this compound as one of the raw materials.
Potassium ferricyanide is also used in wool dyeing.
This compound can also be used as a laboratory reagent. Several organic reactions are conducted by employing this compound as a mild oxidizing agent.
FAQs on Potassium Ferricyanide: Key Properties, Uses, and Safety
1. What is potassium ferricyanide and what is its chemical formula?
Potassium ferricyanide is an inorganic coordination compound with the chemical formula K₃[Fe(CN)₆]. It is characterised by its bright red crystalline solid form and is also known by its IUPAC name, Potassium hexacyanidoferrate(III). The iron atom at the centre of the complex is in the +3 oxidation state.
2. What are the key physical properties of potassium ferricyanide?
Potassium ferricyanide is a bright red crystalline solid with no significant odour. It is highly soluble in water, with its solubility increasing as the temperature rises (from approximately 330 g/L in cold water to 775 g/L in hot water). However, it is only slightly soluble in alcohol and is not soluble in nonpolar solvents.
3. What are the main uses and applications of potassium ferricyanide?
Potassium ferricyanide is a versatile chemical with several important applications in both laboratory and industrial settings. Its key uses include:
Blueprint Production: It is a primary component in the cyanotype process, which produces the characteristic blue-and-white architectural and engineering drawings known as blueprints.
Qualitative Analysis: It serves as a sensitive reagent to test for the presence of ferrous ions (Fe²⁺), forming a deep blue precipitate called Turnbull's blue.
Photography: In traditional photography, it is used in toning solutions and to reduce the density of silver in negatives and positives.
Industrial Processes: It is employed in the hardening of iron and steel, in electroplating, and as an oxidising agent in certain organic syntheses.
4. What are the primary safety concerns and hazards associated with potassium ferricyanide?
Under normal conditions, potassium ferricyanide has relatively low toxicity. However, it is a mild irritant to the eyes and skin, and appropriate safety gear should be worn when handling it. The most significant hazard is its reaction with strong acids. This reaction can decompose the compound and release highly toxic hydrogen cyanide (HCN) gas, which is extremely dangerous if inhaled. Therefore, it must be stored away from acids.
5. What is the fundamental difference between potassium ferricyanide and potassium ferrocyanide?
The primary difference lies in the oxidation state of the central iron atom. In potassium ferricyanide (K₃[Fe(CN)₆]), the iron is in the +3 oxidation state, making the complex an anion [Fe(CN)₆]³⁻. In potassium ferrocyanide (K₄[Fe(CN)₆]), the iron is in the +2 oxidation state, forming the anion [Fe(CN)₆]⁴⁻. This difference in oxidation state also affects their colour (ferricyanide is red, ferrocyanide is yellow) and their chemical reactivity, with ferricyanide acting as an oxidising agent and ferrocyanide as a reducing agent.
6. How is the IUPAC name for K₃[Fe(CN)₆] determined from its structure?
The IUPAC name, Potassium hexacyanidoferrate(III), is determined by following specific nomenclature rules for coordination compounds. First, the cation (Potassium) is named. For the anionic complex [Fe(CN)₆]³⁻, the ligands are named first (six cyanide ligands become 'hexacyanido'). Since the complex is an anion, the metal's name (Iron) is changed to end in '-ate' (ferrate). Finally, the oxidation state of the iron, which is +3, is written in Roman numerals in parentheses (III).
7. Why does potassium ferricyanide produce a deep blue colour when it reacts with ferrous (Fe²⁺) salts?
This colour change is due to the formation of a coordination polymer known as Turnbull's blue, which is structurally identical to Prussian blue. When potassium ferricyanide, containing the [Fe(CN)₆]³⁻ complex, is added to a solution with Fe²⁺ ions, an electron transfer reaction occurs. The Fe²⁺ ions are oxidised to Fe³⁺, and the Fe³⁺ in the complex is reduced to Fe²⁺. These newly formed ions then combine to create the intensely coloured Fe₄[Fe(CN)₆]₃ precipitate. This highly visible and specific reaction is why it is an excellent indicator for detecting ferrous ions.
