Potassium+Ferrocyanide


 * Potassium ferricyanide ** is the [|chemical compound] with the formula K3[Fe(CN)6]. This bright red salt contains the [|octahedrally] [|coordinated] [|[Fe(CN)63−]] ion. It is soluble in water and its solution shows some green-yellow [|fluorescence].

Potassium ferrocyanide is produced industrially from [|hydrogen cyanide], [|ferrous chloride], [|calcium hydroxide], 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.[|[][|2][|]]

n 19th century, it was used for reading [|palimpsests] and old manuscripts.

The compound has widespread use in [|blueprint] drawing and in [|photography] ( [|Cyanotype] process). [|Iron] and [|copper] [|toning] involve the use of potassium ferricyanide. Potassium ferricyanide is used as an [|oxidizing agent] to remove [|silver] from negatives and positives, a process called dot etching. In [|color photography], potassium ferricyanide is used to reduce the size of color dots without reducing their number, as a kind of manual color correction. The compound is also used to [|harden] [|iron] and [|steel], in [|electroplating] , [|dyeing] [|wool] , as a [|laboratory] [|reagent] , and as a mild [|oxidizing agent] in [|organic chemistry].

It is also used in black-and-white photography with [|sodium thiosulfate] (hypo) to reduce the density of a [|negative] or [|gelatin silver print] where the mixture is known as Farmer's reducer; this can help offset problems from [|overexposure] of the negative, or brighten the highlights in the print. [|[4]]

Potassium ferricyanide is also one of two compounds present in [|ferroxyl indicator solution] (along with [|phenolphthalein] ) which turns blue ( [|Prussian blue] ) in the presence of Fe2+ ions, and which can therefore be used to detect metal oxidation that will lead to rust. It is possible to calculate the number of moles of Fe2+ ions by using a [|colorimeter], because of the very intense color of [|Prussian blue] Fe4[Fe(CN)6]3.

Potassium ferricyanide is often used in physiology experiments as a means of increasing a solution's [|redox potential] (E°' ~ 436 mV at pH 7). As such, it can oxidize reduced cytochrome c (E°' ~ 247 mV at pH 7) in intact isolated mitochondria.

[|Sodium dithionite] is usually used as a reducing chemical in such experiments (E°' ~ −420 mV at pH 7).

Potassium ferricyanide is used in many amperometric [|biosensors] as an [|electron transfer] agent replacing an enzyme's natural electron transfer agent such as [|oxygen] as with the [|enzyme] [|glucose oxidase]. It is used as this ingredient in many commercially available blood [|glucose meters] for use by [|diabetics].

Potassium ferricyanide is the main component of Murakami's etchant for cemented carbides.

Prussian blue
[|Prussian blue], the deep blue pigment in blue printing, is generated by the reaction of K3[Fe(CN)6] with ferrous (Fe2+) ions.

In [|histology], potassium ferricyanide is used to detect ferrous iron in biological tissue, as the stain [|Perls' Prussian blue]. In this reaction, potassium ferricyanide reacts with ferrous iron in acidic solution to produce an insoluble blue pigment, and both the stain and the pigment are commonly referred to as [|Turnbull's blue]. To detect ferric (Fe3+) iron, potassium //ferrocyanide// is used instead; the stain and pigment produced are commonly known as Prussian blue. It has been found that the compound formed in the Turnbull's blue reaction and the compound formed in the Prussian blue reaction are the same unique compound, [|Prussian blue].

Safety
Potassium ferricyanide has very low toxicity, its main hazard being that it is a mild irritant to the eyes and skin. However, under very strongly acidic conditions, highly toxic [|hydrogen cyanide] gas is evolved, according to the equation:

6 H+ + [Fe(CN)6]3− → 6 HCN + Fe3+ [|[9]] The reaction with [|hydrochloric acid] is as follows:

6 HCl + K3[Fe(CN)6] → 6 HCN + FeCl3 + 3 KCl
 * [|IUPAC name] [|[hide]] Potassium hexacyanoferrate(III) ||
 * Other names [|[hide]] Red prussiate

Prussian red

Potassium ferricyanide || [|[show]] || [|[show]] || 464 g/L (20°C) 775 g/L ("hot water") [|[1]] || soluble in [|acid] soluble in water || [|geometry] || [|octahedral] at Fe ||
 * ~ Identifiers ||
 * [|CAS number] || [|13746-66-2]  [[image:http://upload.wikimedia.org/wikipedia/en/thumb/f/fb/Yes_check.svg/7px-Yes_check.svg.png width="7" height="7" caption="Yes"]] ||
 * [|PubChem] || [|26250]  ||
 * [|RTECS number] || LJ8225000 ||
 * [|Jmol] -3D images || [|Image 1] ||
 * [|SMILES]
 * [|InChI]
 * ~ Properties ||
 * [|Molecular formula] || C6N6FeK3 ||
 * [|Molar mass] || 329.24 g/mol ||
 * Appearance || deep red crystals ||
 * [|Density] || 1.89 g/cm3, solid ||
 * [|Melting point] || 300 °C, 573 K, 572 °F ||
 * [|Boiling point] || //decomp.// ||
 * [|Solubility] in [|water] || 330 g/L ("cold water")
 * [|Solubility] || slightly soluble in [|alcohol]
 * ~ Structure ||
 * [|Crystal structure] || [|monoclinic] ||
 * [|Coordination]
 * ~ Hazards ||
 * [|MSDS] || [|MSDS] ||
 * EU Index || Not listed ||
 * [|R-phrases] || [|R20], [|R21] , [|R22] , [|R32] ||
 * [|S-phrases] || [|S26], [|S36] ||
 * [|Flash point] || Non-flammable ||
 * ~ Related compounds ||
 * Other [|anions] || [|Potassium ferrocyanide] ||
 * Other [|cations] || [|Prussian blue] ||

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 are also used in the purification of tin and the separation of copper from molybdenum ores. Potassium ferrocyanide is used in the production of wine and citric acid.[|[][|2][|]] In the laboratory, potassium ferrocyanide is used to determine the concentration of [|potassium permanganate], a compound often used in [|titrations] based on [|redoxreactions]. Potassium ferrocyanide is used in a mixture with potassium ferricyanide and phosphate buffered solution (PBS) to provide a buffer for [|X-Gal], which is used to cleave [|Beta-galactosidase], giving a bright blue visualization where an antibody (or other molecule), conjugated to Beta-gal, has bonded to its target. Potassium ferrocyanide can be used as a fertilizer for plants.[//[|citation needed]//]

Toxicity
Potassium ferrocyanide is nontoxic, although upon contact with strong acid it can release toxic [|hydrogen cyanide] gas. It is not decomposed to cyanide in the body. The toxicity in rats is low, with [|lethal dose] (LD50) at 6400 mg/kg.[|[][|1][|]]