Potassium ferrocyanide
Overview
 
Potassium ferrocyanide is the inorganic compound
Inorganic compound
Inorganic compounds have traditionally been considered to be of inanimate, non-biological origin. In contrast, organic compounds have an explicit biological origin. However, over the past century, the classification of inorganic vs organic compounds has become less important to scientists,...

 with formula K4[Fe(CN)6]•3H2O. It is the potassium salt of the coordination complex
Complex (chemistry)
In chemistry, a coordination complex or metal complex, is an atom or ion , bonded to a surrounding array of molecules or anions, that are in turn known as ligands or complexing agents...

 [Fe(CN)6]4-. This salt forms lemon-yellow monoclinic crystal
Crystal
A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is known as crystallography...

s.
Potassium ferrocyanide is produced industrially from hydrogen cyanide, ferrous chloride, calcium hydroxide
Calcium hydroxide
Calcium hydroxide, traditionally called slaked lime, is an inorganic compound with the chemical formula Ca2. It is a colourless crystal or white powder and is obtained when calcium oxide is mixed, or "slaked" with water. It has many names including hydrated lime, builders lime, slack lime, cal, or...

, the combination of which affords Ca2[Fe(CN)6].11H2O.
Encyclopedia
Potassium ferrocyanide is the inorganic compound
Inorganic compound
Inorganic compounds have traditionally been considered to be of inanimate, non-biological origin. In contrast, organic compounds have an explicit biological origin. However, over the past century, the classification of inorganic vs organic compounds has become less important to scientists,...

 with formula K4[Fe(CN)6]•3H2O. It is the potassium salt of the coordination complex
Complex (chemistry)
In chemistry, a coordination complex or metal complex, is an atom or ion , bonded to a surrounding array of molecules or anions, that are in turn known as ligands or complexing agents...

 [Fe(CN)6]4-. This salt forms lemon-yellow monoclinic crystal
Crystal
A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is known as crystallography...

s.

Synthesis

Potassium ferrocyanide is produced industrially from hydrogen cyanide, ferrous chloride, calcium hydroxide
Calcium hydroxide
Calcium hydroxide, traditionally called slaked lime, is an inorganic compound with the chemical formula Ca2. It is a colourless crystal or white powder and is obtained when calcium oxide is mixed, or "slaked" with water. It has many names including hydrated lime, builders lime, slack lime, cal, or...

, the combination of which affords Ca2[Fe(CN)6].11H2O. This solution is then treated with potassium salts to precipitate the mixed calcium-potassium salt CaK2[Fe(CN)6], which in turn is treated with potassium carbonate to give the tetrapotassium salt.

Chemical reactions

The most famous reaction involves treatment with ferric salts to give Prussian blue
Prussian blue
Prussian blue is a dark blue pigment with the idealized formula Fe718. Another name for the color Prussian blue is Berlin blue or, in painting, Parisian blue. Turnbull's blue is the same substance but is made from different reagents....

. With the approximate composition KFe2(CN)6, this insoluble but deeply coloured material is the blue of blueprint
Blueprint
A blueprint is a type of paper-based reproduction usually of a technical drawing, documenting an architecture or an engineering design. More generally, the term "blueprint" has come to be used to refer to any detailed plan....

ing.

Upon treatment with chlorine
Chlorine
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...

 gas, it converts to potassium ferricyanide
Potassium ferricyanide
Potassium ferricyanide is the chemical compound with the formula K3[Fe6]. This bright red salt contains the octahedrally coordinated [Fe6]3− ion. It is soluble in water and its solution shows some green-yellow fluorescence.-Preparation:...

:
2 K4[Fe(CN)6] + Cl2 → 2 K3[Fe(CN)6] + 2 KCl

This reaction can be used to remove potassium ferrocyanide from a solution. When the two are combined, the product is Prussian blue
Prussian blue
Prussian blue is a dark blue pigment with the idealized formula Fe718. Another name for the color Prussian blue is Berlin blue or, in painting, Parisian blue. Turnbull's blue is the same substance but is made from different reagents....

. Potassium ferrocyanide, potassium ferricyanide, and Prussian blue account for over 97% of cyanides in the environment.

Applications

Potassium ferrocyanide finds many niche applications in industry. It and the related sodium salt are widely used as anti-caking agents for both road salt and table salt. The potassium and sodium ferrocyanides area also used in the the purification of tin and the separation of copper from molybdenum ores. Potassium ferrocyanide is used in the production of wine and citric acid.

In the laboratory, potassium ferrocyanide is used to determine the concentration of potassium permanganate
Potassium permanganate
Potassium permanganate is an inorganic chemical compound with the formula KMnO4. It is a salt consisting of K+ and MnO4− ions. Formerly known as permanganate of potash or Condy's crystals, it is a strong oxidizing agent. It dissolves in water to give intensely purple solutions, the...

, a compound often used in titration
Titration
Titration, also known as titrimetry, is a common laboratory method of quantitative chemical analysis that is used to determine the unknown concentration of an identified analyte. Because volume measurements play a key role in titration, it is also known as volumetric analysis. A reagent, called the...

s based on redox
Redox
Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....

reactions. Potassium ferrocyanide is used in a mixture with potassium ferricyanide and phosphate buffered solution (PBS) to provide a buffer for X-Gal
X-gal
X-gal is an organic compound consisting of galactose linked to a substituted indole. The compound was synthesized by Jerome Horwitz and collaborators in Detroit, MI, in 1964. The formal chemical name is often shortened to less accurate but also less cumbersome phrases such as bromochloroindoxyl...

, which is used to cleave Beta-galactosidase
Beta-galactosidase
β-galactosidase, also called beta-gal or β-gal, is a hydrolase enzyme that catalyzes the hydrolysis of β-galactosides into monosaccharides. Substrates of different β-galactosidases include ganglioside GM1, lactosylceramides, lactose, and various glycoproteins...

, giving a bright blue visualization where an antibody (or other molecule), conjugated to Beta-gal, has bonded to its target.

Trivia

Potassium ferrocyanide can be used as a fertilizer for plants. It is often used as a gardening technique. In an experiment to test this aim, plants were either deprived of nitrogen or given a nitrogen-rich environment while all were exposed to potassium ferrocyanide and potassium ferricyanide. The plants were unable to sustain themselves solely on the cyanides, but the uptake of the cyanides did increase in the absence of nitrogen. Furthermore, the plants appeared to have different methods for the uptake of the two cyanides.

Toxicity

Potassium ferrocyanide itself is nontoxic, although upon contact with strong acid it can release of toxic hydrogen cyanide gas. The lethal dose
Lethal dose
A lethal dose is an indication of the lethality of a given substance or type of radiation. Because resistance varies from one individual to another, the 'lethal dose' represents a dose at which a given percentage of subjects will die...

(LD50) in rats is low, at 6400 mg/kg.

External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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