Potassium Ferrocyanide - K₄Fe(CN)₆

What is Potassium Ferrocyanide?

Potassium ferrocyanide is defined as an inorganic compound having the chemical formula K4Fe(CN)6 (potassium ferrocyanide formula). Potassium ferrocyanide is otherwise called yellow potash prussiate, which is a yellow crystal. It was made with either horn or wool clippings stirring hot potassium carbonate using an iron rod. Potassium ferrocyanide compound can be used for certain iron processes as a developer and as an additive for alkaline pyro developers.

Potassium hexacyanoferrate (II), yellow prussiate of potash are the other names of Potassium Ferrocyanide.

Potassium Ferrocyanide Structure – K4Fe(CN)6

The structure of Potassium Ferrocyanide can be represented as follows:

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Properties of Potassium Ferrocyanide

Let us look at some of the important properties of potassium ferrocyanide


Potassium ferrocyanide

Chemical Formula


Molecular Weight or Molar Mass

368.35 g/mol


1.85 g/cm³

Melting Point

300 °C

Boiling Point

400 °C

Physical Properties of Potassium Ferrocyanide – K4Fe(CN)6


Light yellow, crystalline granules



Hydrogen Bond Acceptor


Covalently-Bonded Unit



Insoluble in ether, ethanol



Chemical Properties of Potassium Ferrocyanide – K4Fe(CN)6

K4[Fe(CN)6] + 6H2SO4 + 6H2O → 2K2SO4 + FeSO4 + 3(NH4)2SO4 + 6CO

  • Potassium ferrocyanide further reacts with ferric chloride and forms potassium chloride and a complex compound Iron (III) potassium hexacyanidoferrate (II). The chemical reaction can be given as follows:

K4[Fe(CN)6] + FeCl3 → KFe[Fe(CN)6] + 3 KCIC

Uses of Potassium Ferrocyanide – K4Fe(CN)6

  • Potassium Ferrocyanide can be used in steel tempering and the engraving process. It is also employed in pigment manufacture and as a chemical reagent.

  • A small amount in hydroquinone and pyro developers tends to lower fog and produce greater density.

  • It is also used in potassium cyanide manufacture, which can be extensively used in gold mining.

  • Besides, Ferro Cyanogen produces the most metal compounds insoluble in water, where a few of which exhibit highly characteristic colours. It serves as a test for both ferric and cupric compounds.

Applications of Potassium Ferrocyanide

The important applications of Potassium ferrocyanide can be listed as follows:

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

  • It is also used in animal feeding.

  • Potassium ferrocyanide is used to determine potassium permanganate concentration in the laboratory, which is a compound often used in titrations according to the redox reactions. Potassium ferrocyanide compound is used in a mixture with the phosphate-buffered solution and potassium ferricyanide to give a buffer for beta-galactosidase. It can be used to cleave X-Gal, producing a bright blue visualization where an antibody (otherwise another molecule), conjugated to the Beta-gal, has bonded to its target. Also, on reacting with Fe(3), it produces a Prussian blue colour. Therefore, it can be used as an identifying reagent for iron in laboratories.

  • Potassium ferrocyanide compound is used as a plant fertilizer.

  • Before 1900 AD, prior to the invention of the Castner process, potassium ferrocyanide compound was the essential source of alkali metal cyanides. Potassium cyanide was produced by decomposing potassium ferrocyanide in this historical process. The chemical reaction can be given as follows:

K4[Fe(CN)6] → 4 KCN + FeC2 + N2

Toxicity of Potassium Ferrocyanide on Salt

Acute oral toxicity of the potassium ferrocyanide is given as 5000mg/kg. It means 350gm for a 70kg human. Although the molecules consist of cyanide ions, they are bound more tightly to the iron atom and stay with the iron right through the human digestive system.

The amount that is added to the table salt for anti-caking is of the order of 20 mg/kg of sodium chloride, which means that we would have to eat a truckload of table salt to reach the potassium ferrocyanide’s toxic level. Of course, the salt would kill us long before the potassium ferrocyanide.

Market Availability of Potassium Ferrocyanide

Potassium ferrocyanide compound exists as odourless, light yellow crystals that are soluble in water but insoluble in alcohols. This compound is also referred to as either yellow prussiate of potassium hexacyanoferrate (II) or potash. Potassium ferrocyanide is manufactured from potassium hydroxide and hydrogen ferrocyanide. This compound is not considered to be toxic, but it is dangerous when mixed with other chemicals or heated with them. It can be used commonly for the production of pigments & dyes, steel & iron, pharmaceutical, and many other chemicals, and as a food additive.

FAQs (Frequently Asked Questions)

1. Explain if potassium ferrocyanide is toxic?

Potassium ferrocyanide is not considered to be toxic to humans because it is not decomposed to cyanide in the human body. However, if this compound gets mixed with strong acids, it can be potentially fatal.

2. Give the uses of potassium ferrocyanide.

Potassium ferrocyanide has several uses in many industries. This compound, including the related sodium salt (also called sodium ferrocyanide), is commonly used for both table salt and road salt as anti-creating agents. In addition, sodium and potassium ferrocyanides can be used to purify isolate and tin copper from molybdenum ores. Potassium ferrocyanide can also be used for citric acid and wine production.

3. How is potassium ferricyanide prepared from potassium ferrocyanide?

A 100 grams of potassium ferrocyanide solution in 1000 ml of water should be saturated with chlorine and stirred regularly until the solution exhibits a fine, deep red colour.

4. Give the modern and historical production of potassium ferrocyanide.

Historical Production

Potassium ferrocyanide compounds have traditionally been made from organic compounds containing iron filings, nitrogen and potassium carbonate. Common carbon and nitrogen sources were leather scrap, torrified horn, dried blood, or offal.

Modern Production

Potassium ferrocyanide can be produced industrially from ferrous chloride, hydrogen cyanide, and calcium hydroxide, the combination of which affords Ca2[Fe(CN)6]·11H2O. This solution is then combined with potassium salts to precipitate the salt of mixed calcium-potassium CaK2[Fe(CN)6], which is then treated with potassium carbonate for the processing of tetra potassium salt.

5. Potassium ferrocyanide is which type of salt?

Potassium ferrocyanide is a kind of potassium salt with the coordination complex [Fe(CN)6]4. This specific salt forms the lemon-yellow monoclinic crystals.