Potassium Ferricyanide - K₃[Fe(CN)₆]

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What is Potassium Ferricyanide?

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.

FAQ (Frequently Asked Questions)

1. Is potassium ferricyanide toxic?

Potassium ferricyanide is known for its relatively low toxicity. However, the major hazard associated with this compound is that it is mildly irritant to both eyes and skin. It is also noted that the highly toxic gas hydrogen cyanide is produced when this compound is placed under more strongly acidic conditions. Thus, proper care must be taken in potassium ferricyanide storage.

2. List some uses of potassium ferricyanide.

A few uses of potassium ferricyanide can be listed below:

  • Potassium ferricyanide is used as an oxidizing agent to eliminate silver from both positive and negative colours.

  • It is also aware that this compound has several applications in the field of photography. For example, potassium ferricyanide can be employed in numerous photographic print toning processes.

  • This can also be used during steel and iron hardening.

  • Sometimes, the electroplating procedure is carried out with this compound as one of its raw materials.

  • The potassium ferricyanide usage in wool dyes is also seen.

3. Comment on the solubility of potassium ferricyanide in water.

Potassium ferricyanide is known for its extreme solubility of water. For example, the solubility of this compound in cold water is about 330 grams per litre.

The solubility of potassium ferricyanide at a temperature of 20 degrees celsius in water is estimated to be approximately equivalent to 464 grams per litre. Eventually, the solubility of this compound in hot water can reach a maximum of 775 grams per litre.

4. List an application of Potassium Ferricyanide?

Potassium ferricyanide can be used to determine the ferric reducing power potential of a sample (such as chemical compound extract). Such measurement can be used to determine the sample antioxidant property.

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