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Potassium Ferrocyanide [K4Fe(CN)6] or “Green salt” is an inorganic compound. It consists of potassium, iron, carbon, and nitrogen. It is also known as yellow potash prussiate (a yellow crystal). It was first discovered by French chemist Pierre Joseph Macquer in 1752 by reacting Prussian blue (C18Fe7N18 ) and potassium hydroxide (KOH). Sometimes it is used for the detection of metals in the analytical laboratory. In this article, we will discuss potassium ferrocyanide, its properties, and its applications in detail.
What is Potassium Ferrocyanide (K4Fe(CN)6?
Potassium Ferrocyanide is a chemical compound whose chemical formula is [K4Fe(CN)6]. It is a kind of potassium salt consisting of a central metallic atom (Fe). This salt forms lemon-yellow monoclinic crystals.
- Its IUPAC name is Potassium Hexacyanoferrate(II).
- Potassium Ferrocyanide is produced by mixing Hydrogen cyanide, iron(II) chloride, and calcium hydroxide. This is the modern production method of Potassium Ferrocyanide.
- It is mainly used as a coloring agent in the food industry.
- It appears in light yellow crystalline form.
Structure of Potassium Ferrocyanide
The following is the structure of Potassium Ferrocyanide:
 Potassium Ferrocyanide Physical Properties of Potassium Ferrocyanide
The physical properties of Potassium Ferrocyanide are discussed below:
- Potassium Ferrocyanide is soluble in water.
- The solubility in water increases with the increase in temperature. In cold water the solubility is roughly 330gm/liter and in hot water it is more than 770gm/liter.
- The density of Potassium Ferrocyanide is 1.85 g/cm3.
- Boiling point of it is 400°C or 752℉.
- Melting point of it is around 71℃.
- The molecular weight of it is 1.85g/cm3
- It appears as a light yellow crystalline granule.
- Potassium Ferrocyanide is insoluble in ether and ethanol
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Appearance
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Light yellow crystalline granules form
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Odor
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Odorless
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Covalently-Bonded Unit
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10
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Hydrogen Bond Acceptor
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12
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IUPAC name
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Potassium Hexacyanoferrate II
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Chemical Properties of Potassium Ferrocyanide
The Chemical properties of Potassium Ferrocyanide are discussed below:
K4[Fe(CN)6] + 6H2SO4 + 6H2O → 2K2SO4 + FESO4 + 3(NH4)2SO4 + 6CO
- Potassium Ferrocyanide reacts with ferric chloride to form a complex compound of Iron (III) Potassium Hexacyanidoferrate II and potassium chloride. The chemical reaction is given below:
K4Fe(CN)6 + FeCl3 → KFe[Fe(CN)6] + 3KCL
- By decomposing Potassium Ferrocyanide, potassium cyanide is produced. The chemical reaction is as follows:
K4[Fe(CN)6 → 4KCN + FeC2 + N2
Chemical Reactions of Potassium Ferrocyanide
Although, we have already discussed some chemical reactions with the chemical properties, a few more reactions are discussed below:
- When Potassium Ferrocyanide reacts with chlorine gas, it produces potassium ferricyanide. The chemical equation for this reaction is
2K4[Fe(CN)6] + Cl2 → 2K3[Fe(CN)6] + 2KCL
- Hydrogen peroxide oxidize Potassium Ferrocyanide to form potassium ferricyanide. The chemical equation for this reaction is
2K4[Fe(CN)6] + H2O2 → 2K3[Fe(CN)6] + 2KOH
Chemical Reactions Involving Potassium Ferrocyanide as a Catalyst
- It is used in the form of catalyst in photographic, biochemical and analytical chemistry.
- It is also an effective and gentle catalyst for the synthesis of benzothiazoles and benzoxazoles.
Uses of Potassium Ferrocyanide
- Potassium Ferrocyanide or K4[Fe(CN)6] is used to harden iron and steel.
- By decomposing Potassium Ferrocyanide we can produce potassium cyanide which is heavily useful in Gold mining.
- It is used in the production of citric acid and wine.
- It is used as an oxidizing agent in organic chemistry.
- It is also used in food and pharmaceutical industries as a coloring agent. Though it is not a food additive.
- It does not affect food safety, the World Health Organization confirms that Potassium Ferrocyanide is safe for consumption when used at approved levels.
Toxicity of Potassium Ferrocyanide
- Potassium cyanide is toxic but Potassium Ferrocyanide is not. It is used in salt to give it anti-caking properties.
- If it is mixed with other chemicals or if it is heated with any chemical compound, Potassium Ferrocyanide is very dangerous.
- When it is used as a coloring agent in food items at an approved level by W.H.O. it is safe to consume and does not affect food safety.
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FAQs on Potassium Ferrocyanide
Is Potassium Ferrocyanide soluble in Water?
Yes, Potassium Ferrocyanide is soluble in water. Its solubility increases with the increase in temperature.
Potassium Ferrocyanide is which type of salt?
Potassium Ferrocyanide is a kind of potassium salt consisting a central atom which is metallic (Fe). This salt forms lemon-yellow monoclinic crystals.
What happens when Potassium Ferrocyanide reacts with sulfuric acid?
When Potassium Ferrocyanide reacts with H2SO4 the reaction produces potassium sulfate, carbon monoxide, ferrous sulfate, ammonium sulfate.
K4[Fe(CN)6] + 6H2SO4 + 6H2O → 2K2SO4 + FESO4 + 3(NH4)2SO4 + 6CO
Is Potassium Ferrocyanide toxic?
Potassium cyanide is toxic but Potassium Ferrocyanide is not. When it is used in food items at an approved level by W.H.O. it is safe to consume and does not affect food safety.
How can Potassium Ferricyanide be prepared from Potassium Ferrocyanide?
We have to mix a 100 g potassium ferrocyanide solution in 1000 ml water and the mixture must be saturated with chlorine, and stirred constantly until the solution shows a deep fine red color. This is the process to prepare Potassium Ferricyanide from Potassium ferrocyanide.
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