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Potassium Ferrocyanide is a yellow crystalline salt made from the cyanogen compounds. It is an inorganic compound obtained as a by-product of the carbonization of coal. Potassium Ferrocyanide can directly be received by the reaction of potassium cyanide [KCN] with ferrous salts.
- Potassium Ferrocyanide is widely used in making iron blue pigments.
- It is an inorganic compound with the formula K4[Fe(CN)6].
- It is a component of amperometric biosensors in the form of electron transfer agents.
- Potassium Ferrocyanide is manufactured by passing chlorine through a solution.
- The product is obtained by separation from the chlorine solution.
- It is used as a colouring agent in the food and pharmaceutical industries.
- The colouring agent does not affect the safety of the food.
- Potassium Ferrocyanide is a highly stable compound.
Read More: Precipitation Titration
Key Terms: Potassium Ferrocyanide, Ferrous Salts, Iron, Potassium Carbonate, Chlorine, Potassium Hexacyanoferrate, Solubility, Potash
What is Potassium Ferrocyanide?
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Potassium Ferrocyanide is an inorganic compound with the chemical formula K4[Fe(CN)6]. It is also referred to as yellow potash prussiate, which is a yellow crystal substance.
- It was made up of wool or horn clippings stirring hot potassium carbonate with an iron rod.
- Potassium ferrocyanide is basically used for certain iron processes as a developer.
- It is used as an additive for developers of alkaline pyro.
- Other names of Potassium ferrocyanide include yellow prussiate of potash and potassium hexacyanoferrate (II).
Read More: Ferrous Sulphate
Potassium Ferrocyanide Structure
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The molecular formula of the Potassium Ferrocyanide is K4[Fe(CN)6]. Its structure is given in the image provided below.
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General Properties of Potassium Ferrocyanide
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The general properties of Potassium Ferrocyanide are provided in the table below:
| Category | Data |
|---|---|
| K4[Fe(CN)6] | Potassium Ferrocyanide |
| Density | 1.85 g/cm³ |
| Molecular Weight/ Molar Mass | 368.35 g/mol |
| Boiling Temperature | 400 °C |
| Melting point | 300 °C |
| Chemical Formula | K4Fe(CN)6 |
Read More: Column chromatography
Physical Properties of Potassium Ferrocyanide
The physical properties of Potassium Ferrocyanide are as follows:
- The IUPAC name of Potassium Ferrocyanide is Potassium Hexacyanidoferrate (II) C6FeK4N6.
- It was made by stirring hot potassium carbonate with wool or horn clipping with an iron rod.
- Another type ferrocyanide is Potassium ferricyanide with the chemical formula K3[Fe (CN)6].
- This bright red salt consists of the coordination compound [Fe (CN)6]3−.
- It shows some green-yellow luminous and is solution is thus shown solubility in water.
- The colour of this complex compound is due to unpaired electrons.
- The molecular weight of potassium ferrocyanide is 368.35 g/mol.
- Its density is approximately 1.85 g/cm3.
- The solubility of the compound in cold water is known to be roughly 330 grams per litre.
- When temperature is increased to 20 degrees Celsius, the solubility of potassium ferrocyanide becomes equal to 464 grams per litre.
- The solubility of this compound in hot water is known to be more than 775 grams per litre.
- It is also found to be soluble in some particular acids.
| Category | Data |
|---|---|
| Odour | No odour |
| Appearance | Light yellow crystalline granules |
| Covalently-Bonded Unit | 10 |
| Hydrogen Bond Acceptor | 12 |
| Complexity | 127 |
| Solubility | Insoluble in ethanol and ether |
Read More: Aqua regia
Chemical Properties of Potassium Ferrocyanide
The chemical properties of Potassium Ferrocyanide are as follows:
- Potassium ferrocyanide reacts with sulphuric acid in a medium aqueous form of ferrous sulphate, potassium sulphate, carbon monoxide, and ammonium sulphate.
The chemical reaction is shown as:
K4[Fe(CN)6] + 6H2SO4 + 6H2O → 2K2SO4 + FeSO4 + 3(NH4)2SO4 + 6CO
- Potassium ferrocyanide reacts with ferric chloride and forms potassium chloride [KCL] and a complex compound Iron (III) potassium Hexacyanidoferrate (II).
The chemical reaction is shown as:
K4[Fe(CN)6] + FeCl3 → KFe [Fe(CN)6] + 3 KCL
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Preparation of Potassium Ferrocyanide
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Potassium hexacyanoferrate (II), K4Fe (CN)6·3H20, is procured commercially from gasworks spent oxide (which contains Prussian blue) by treatment with lime and successive treatment of the solution with a soluble potassium salt, the less soluble potassium hexacyanoferrate (II) can be crystallized from this mixture.
![Preparation of Potassium Ferrocyanide- K4[Fe(CN)6]](https://images.collegedunia.com/public/image/3d7925dd51422d0c3b49440db3d1f5e0.png)
In the laboratory it is easily prepared by treating aqueous iron (II) sulphate with an excess of potassium cyanide[KCN], the initially precipitated iron (II) cyanide dissolves upon boiling in the excess of potassium cyanide[KCN] solution and the ferrocyanide crystallizes on cooling.
Read More: Noble gases
Applications of Potassium Ferrocyanide
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The applications of Potassium Ferrocyanide are as follows:
- Potassium Ferrocyanide is used to harden iron and steel.
- It is widely used in electroplating and in dyeing wool.
- Potassium Ferrocyanide is used as a mild oxidizing agent in organic chemistry.
- It is used as moderately used as a strong oxidizer when coupled with ferricyanide.
- It is used as a developer for some iron processes and as an additive for alkaline pyro developers.
- This compound is used in the production of citric acid and wine.
- Potassium ferrocyanide is used in titration according to the redox reactions.
- It is also used in a mixture of phosphate-buffered solution and a buffer for bet-galactosidase.
- Potassium Ferrocyanide is also utilized as an oxidant for catalyst regeneration in dihydroxylations.
- It can also be used as electron transfer agents
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Toxic Nature of Potassium Ferrocyanide
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- Potassium Ferrocyanid when mixed with other chemicals or gets heated with any chemical is very dangerous.
- Potassium Cyanide releases cyanide anion when it is consumed by a person.
- It is strongly bonded with ferrous ions and thus did not get hydrolyzed.
- The LD50 value of potassium ferrocyanide is almost the same as common salt
Read More: Cathode Ray Experiment(JJ Thomas)
Things to Remember
- Potassium Ferrocyanide is the chemical compound with the formula K3[Fe (CN)6].
- It is a yellow crystal also known as yellow prussiate of potash.
- It was made by stirring hot potassium carbonate with wool or horn clipping with an iron rod.
- The Melting Point and boiling point of Potassium Ferrocyanide is 69 – 71 ° C & 400 °C respectively.
- It is also used as a mild oxidizing agent in organic chemistry.
- It is used as moderately used as a strong oxidizer when coupled with ferricyanide.
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Sample Question
Ques: When we mix Potassium Ferrocyanide with cadmium ions then what is colour of the precipitate obtained in reaction. (A) Bluish white (B) Dirty White (C)Greenish white (D) White (3 marks)
Ans: The reaction of Potassium Ferrocyanide ion with different ions-
- When Potassium Ferrocyanide is reacted with Fe3+ we get Prussian blue precipitate of Ferric ferrocyanide (Fe4{Fe [CN ]6}3).
- When Potassium Ferrocyanide K4[Fe (CN)6] reacts with Zn+2 we get a Greenish white precipitate called Zn2[Fe {CN}6].
- When Potassium Ferrocyanide K4[Fe (CN)6] react with Cd2+ we get bluish white precipitate Cd2[Fe (CN)6].
- When Potassium Ferrocyanide K4[Fe (CN)6] reacts with Cu2+ we get reddish-brown precipitate called Cu2[Fe (CN)6]
- So, the answer is Bluish white
Ques: Find the colour of the precipitate when the acetic acid (CH3COOH) and potassium ferrocyanide K4[Fe (CN)6] are mixed with a copper salt. (A) Blue (B) Black (C) Brown (D) White (2 marks)
Ans: As acetic acid is a weak acid (CH3COOH), it will not react the reaction will only occur in potassium ferrocyanide and copper salt, the reaction thus follows will:
2CuSO4 + K4[Fe (CN)6] = Cu2[Fe (CN)6] +K2SO4
the product we got is called Cupricferrocyanide which gives the precipitate of Reddish-brown colour. So, the most appropriate answer is Reddish Brown Colour
Ques: Find what happens when potassium ferrocyanide is added to a ferric salt solution. (2 marks)
Ans: Potassium Ferrocyanid is an inorganic compound which was made by stirring hot potassium carbonate with wool or horn clipping with an iron rod.When potassium ferrocyanide is added to a ferric salt solution prussian blue colour complex which is called ferri-ferrocyanide is formed.
Ques: Calculate can’t Hoff factor if potassium ferrocyanide is 80% ionized. (4 marks)
Ans: If potassium ferrocyanide is 80% ionized we get a degree of dissociation which is then represented by the sign ‘α’. If we convert it from the per cent form to fraction from it will be represented as
80\100 = 0.8
Potassium ferrocyanide is ionised as, K4[Fe (CN)6] -> 4K+ + [Fe (CN)6]4-
then we get the number of ions formed from 1 molecule of electrolyte; 1 molecule of potassium ferrocyanide gives 4 ions of potassium and 1 ions of [Fe (CN)6]4-
So if we represent it by ‘n’ then
n = 4+1 = 5
Now used it in the formula of can’t Hoff
i = 1 + (n-1) ‘α’ ( this formula is valid for any dissociation reaction )
then i = 1 + (5-1) 0.8
= 1 + 4 × 0.8
= 1 + 3.2
= 4.2
Answer is the i= 4.2
Ques: What are the uses of potassium ferrocyanide. (5 marks)
Ans: The uses of potassium ferrocyanide are:
- Potassium Ferrocyanide is used to harden iron and steel also as a laboratory reagent.
- It is also used as a mild oxidizing agent in organic chemistry.
- It is used as moderately used as a strong oxidizer when coupled with ferricyanide.
- It is used as a developer for some iron processes and as an additive for alkaline pyro developers.
- This compound is used in the production of citric acid and wine.
- Potassium ferrocyanide is chiefly used to determine potassium permanganates concentration in the laboratory, which itself is a compound and frequently used in titration according to the redox reactions.
Ques: Mention some of the physical properties of potassium ferrocyanide. (4 marks)
Ans: The physical properties of potassium ferrocyanide are:
- Potassium Ferrocyanide is the chemical compound with the formula K3[Fe (CN)6] is a yellow crystal also known as yellow prussiate of potash. It was made by stirring hot potassium carbonate with wool or horn clipping with an iron rod.
- Another type is Potassium ferricyanide which creates a bright red salt consists of the coordination compound [Fe (CN)6]3−.
- It shows some green-yellow luminous and is solution is thus shown solubility in water.
- The colour of this complex compound is due to unpaired electrons.
- The crystal field theory, K4[Fe (CN)6] KX4[Fe (CN)X6] has no unpaired electrons so it has to be colourless.
- The molecular weight of potassium ferrocyanide is 368.35 g/mol and its density is 1.85 g/cm3.
- The Melting Point and boiling point of Potassium Ferrocyanide is 69 – 71 ° C & 400 °C respectively.
Ques: Is potassium ferrocyanide toxic? Explain. (3 marks)
Ans: Potassium ferrocyanide is not decomposed to cyanide in the body, therefore it is not toxic to humans.
- This compound is not considered as toxic in nature but when mixed with other chemicals or gets heated with any chemical it caused be very dangerous
- While potassium Cyanide is a toxic substance and releases the cyanide anion when it is consumed by a person, the case of potassium ferrocyanide is different it is non – toxic in nature.
- It is strongly bonded with ferrous ions and thus did not get hydrolyzed.
Ques: How can potassium ferricyanide be prepared from potassium ferrocyanide. (2 marks)
Ans: To prepare potassium ferricyanide from potassium ferrocyanide, a 100 g potassium ferrocyanide solution in 1000 ml water must be saturated with chlorine, and stirred constantly until the solution shows a fine, deep red colour.
Ques: What are the general properties of potassium ferricyanide. (4 marks)
Ans: The general properties of potassium ferricyanide are as follows:
| Category | Data |
|---|---|
| K4[Fe(CN)6] | Potassium Ferrocyanide |
| Density | 1.85 g/cm³ |
| Molecular Weight/ Molar Mass | 368.35 g/mol |
| Boiling Temperature | 400 °C |
| Melting point | 300 °C |
| Chemical Formula | K4Fe(CN)6 |
Ques: Calculate can’t Hoff factor if potassium ferrocyanide is 20% ionized. (4 marks)
Ans: If potassium ferrocyanide is 80% ionized we get a degree of dissociation which is then represented by the sign ‘α’. If we convert it from the per cent form to fraction from it will be represented as
20\100 = 0.2
Potassium ferrocyanide is ionised as, K4[Fe (CN)6] -> 4K+ + [Fe (CN)6]4-
then we get the number of ions formed from 1 molecule of electrolyte; 1 molecule of potassium ferrocyanide gives 4 ions of potassium and 1 ions of [Fe (CN)6]4-
So if we represent it by ‘n’ then
n = 4+1 = 5
Now used it in the formula of can’t Hoff
i = 1 + (n-1) ‘α’ ( this formula is valid for any dissociation reaction )
then i = 1 + (5-1) 0.2
= 1 + 4 × 0.2
= 1 + 0.8
= 1.8
Answer is the i= 4.2
Ques: What are the reactions involved in the chemical properties of the potassium ferrocyanide. (2 marks)
Ans: The reactions involved in the chemical properties of the potassium ferrocyanide are as follows:
K4[Fe(CN)6] + 6H2SO4 + 6H2O → 2K2SO4 + FeSO4 + 3(NH4)2SO4 + 6CO
K4[Fe(CN)6] + FeCl3 → KFe [Fe(CN)6] + 3 KCL
Ques: What are the advantages of using potassium ferrocyanide. (3 marks)
Ans: The advantages of using potassium ferrocyanide are as follows:
- Potassium Ferrocyanide is highly soluble in water.
- It is used as food coluring agent but does not hamper the safety of food.
- Potassium Ferrocyanide is a highly stable compound with low melting point.
- The stains of Potassium Ferrocyanide can easily be washed with cold water.
- It is non-flammable and does not contain any carcinogen.
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