Potassium Ferrocyanide

Dhristi JEE 2022-24

What is Potassium Ferrocyanide?

Potassium Ferrocyanide K4(Fe(CN)6) is used in the food and pharmaceutical industries for colouring purposes. The potassium ferrocyanide is used as a colourant in sugar, in food products such as baked goods, pasta, fruit, jelly and pie fillings, dairy products, meat and fish products, coffee, and chewing gum; and as a component in medicines and pharmaceuticals such as vaccines, vitamins, and antibiotics. It is commonly used in the manufacturing of dry-matter-free foods and food colourants, but there is the increased use of foods containing small amounts of added potassium ferrocyanide. This colourant is not a food additive and does not affect food safety. Potassium Ferrocyanide is usually added to sugar to improve the colour of the food product. It is approved for use as a colourant in food and as a component of medicines and medical foods for colour control.


Advantages

  • Potassium Ferrocyanide does not affect food safety.

  • Potassium ferrocyanide is water-soluble and stable to hydrolysis and does not generate toxic material.

  • Highly stable.

  • Does not stain the mouth, lips, teeth or fingers.

  • Stains are washable with cold water.

  • Easy to handle.

  • High stability and low melting point.

  • Colour is permanent and will not run.

  • Colour strength can be varied by adjusting the pH and amount of ingredients.

  • Colourants with this property help to produce clear and attractive baked goods.

  • It is a good absorber of moisture from sugar.

  • It is not a carcinogen.

  • It does not oxidise rapidly and can be used in large amounts.

  • It is safe for use with children, pregnant women, the elderly, and the sick.

  • It is non-flammable.

  • Low cost.

  • It does not react with most other food products.

  • It does not alter the taste of the food to which it is added.

  • Potassium ferrocyanide does not harm the environment.


Applications

Potassium ferrocyanide is used as a colourant in foods and beverages such as jam, jelly, marmalade, and baking powder. It can also be used in some medicines and medicines containing calcium or iron. It is also a component of some medical food. Potassium ferrocyanide can also be used to colour some medical foods for specific groups of patients such as those with kidney or cardiac problems.


History

Ferrocyanide salts were first produced in the 1840s. Potassium ferrocyanide was produced in 1891 by Thomas Graham and Alfred Rose of the English Pharmaceutical Society. This was the first successful commercial production of potassium ferrocyanide.


Potassium ferrocyanide was first used as a colourant in the food industry in the 1890s. It was then used to colour gelatin for food products, such as jam and marmalade, to distinguish them from cheaper, synthetic-coloured products. Many patents were obtained to protect the new colourant.


It was authorised for use of ferrocyanide as a food colouring in the 1930s. It was approved for use in jelly, jam, marmalade, candy, and baking powder.


There is some dispute about the name potassium ferrocyanide. It is also known as “green salt.”


Benefits:

  • It is a good colourant because it gives the product a bright green colour. It does not lose colour when it is heated or exposed to sunlight.

  • It has fewer disadvantages than a synthetic colourant.

  • It is safe for use in food products.

  • It may be used in a broad range of food products.

  • It is not volatile, so there is no risk of it burning the mouth.

  • It does not cause cancer.

  • It is inexpensive.


About Potassium Ferrocyanide -K4(Fe(CN)6)

Potassium Ferrocyanide -K4(Fe(CN))6 is a ferricyanide salt or a potassium salt. It is a colourless or yellowish solid material. As a salt, it is a strong acid salt. It is soluble in water, ether and other solvents.


Potassium ferrocyanide -K4(Fe(CN)6) is used as a catalyst in photographic, biochemical and analytical chemistry. It is mainly used as a potassium salt for the preparation of potassium ferrocyanide - K4(Fe(CN))6. Potassium ferrocyanide -K4(Fe(CN)6) is also called potassium ferricyanide -K4(Fe(CN))6, potassium ferricyanide -K4(Fe(CN)2), potassium ferricyanide -K4(Fe(CN)2), potassium ferricyanide -K4(Fe(CN)2) and potassium ferricyanide -K4(Fe(CN)3). Potassium ferrocyanide -K4(Fe(CN)6) is also called potassium dichromate -K4Cr2O7).


Potassium ferrocyanide - K4(Fe(CN)6) is used in many processes in the analytical laboratory for the detection and determination of metals. It is used in analytical chemistry for the determination of trace amounts of copper and iron, for the determination of iron in the steel and for the analysis of copper and iron. It is used to detect the presence of copper in iron ore, the determination of iron and copper in aluminium by atomic absorption and for the identification and determination of copper in a solution. It is used in analytical chemistry for the determination of arsenic, cadmium, lead and zinc in the determination of arsenic and lead in ore, lead in steel and in steel of all grades.


The use of potassium ferrocyanide - K4(Fe(CN)6) as an indicator in the precipitation titrimetric procedure is widely known. The reaction is carried out at low pH values in the presence of various bases and the excess of the base is determined by titration with acid. The precipitation with potassium ferrocyanide - K4(Fe(CN)6) in the presence of various metals is also performed. The precipitation of iron (II) with potassium ferrocyanide - K4(Fe(CN)6) is used for the identification and determination of iron in iron ore, the determination of iron in the steel and for the identification of copper in an aluminium alloy. The precipitation of aluminium in the presence of potassium ferrocyanide -K4(Fe(CN)6) can be used for the identification and determination of aluminium in an aluminium alloy.


A simple extraction procedure for the determination of aluminium in the range 5-70 microg/g using 2-(p-toluenesulfonic acid)-3,6-diamino-9-ethyl carbazole - DAEC is described. The results obtained by the extraction and chelation method agree with those obtained by the electrothermal atomic absorption spectrometry.


Potassium ferrocyanide is defined as an inorganic compound having the chemical formula K4(Fe(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 –K4(Fe(CN)6)

The structure of Potassium Ferrocyanide can be represented as follows:


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


Properties of Potassium Ferrocyanide

IUPAC Name

Potassium ferrocyanide

Chemical Formula

K4(Fe(CN)6)

Molecular Weight or Molar Mass

368.35 g/mol

Density

1.85 g/cm³

Melting Point

300 °C

Boiling Point

400 °C


Physical Properties of Potassium Ferrocyanide – K4(Fe(CN)6)

Appearance

Light yellow, crystalline granules

Odour

Odourless

Hydrogen Bond Acceptor

12

Covalently-Bonded Unit

10

Solubility

Insoluble in ether, ethanol

Complexity

127


Chemical Properties of Potassium Ferrocyanide – K4(Fe(CN)6)

\[ K_{4}(Fe(CN)_{6}) + 6H_{2}SO_{4} + 6H2O \rightarrow  2K_{2}SO_{4} + FeSO_{4} + 3(NH_{4})_{2}SO_{4} + 6CO \]

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

\[ K_{4}(Fe(CN)_{6}) + FeCl_{3} \rightarrow KFe[Fe(CN)_{6}] + 3 KCIC \]


Uses of Potassium Ferrocyanide – K4(Fe(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 of 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 them 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 an anti-caking agent 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 the 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. The 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 visualisation 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, the 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:

\[ K_{4}(Fe(CN)_{6}) \rightarrow  4 KCN + FeC_{2} + N_{2} \]


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 compounds exist 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 and dyes, steel and iron, pharmaceutical, and many other chemicals, and as a food additive.

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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?

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 color.

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.

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