Potassium hexacyanoferrate (III) is also termed Red prussiate of Potash or Potassium ferricyanide whose chemical formula is K3[Fe(CN)6]. It was discovered by Leopold Gmelin in the year 1822. Potassium Hexacyanoferrate III is composed of potassium, iron, carbon, and nitrogen elements. It appears as deep red crystals, which decompose on heating. This compound contains the octahedrally coordinated [Fe(CN)6]3− ion. It is soluble in water and its solution exhibits slight green-yellow fluorescence. When it reacts with a strong acid, highly toxic hydrogen cyanide gas is evolved. It is prepared when chlorine is passed through a solution of potassium ferrocyanide. Potassium ferricyanide is widely used in photography and blueprint drawing. It is also used in calico printing, electroplating, and wool dyeing, as a laboratory reagent, and as an oxidant in organic chemistry. It is used to formulate Murakami’s etchant, which is used by metallographers.
Structure of Potassium Hexacyanoferrate (III)
Preparation of Potassium Hexacyanoferrate (III)
- When chlorine is passed through a solution of potassium ferrocyanide, potassium Hexacyanoferrate III is produced.
2K4[Fe(CN)6] + Cl2 → 2K3[Fe(CN)6] + 2KCl
Physical Properties of Potassium Hexacyanoferrate (III)
| Chemical Formula | K3[Fe(CN)6] |
|---|---|
| Other Names |
Potassium ferricyanide, Red prussiate of Potash, Prussian red |
| Molar Mass | 329.24 g/mol |
| Appearance | Deep red crystals |
| Density | 1.89 g/cm3 |
| Melting Point | 300 °C |
| Boiling Point | Decomposes |
| Solubility | Soluble in water, acid, and slightly soluble in alcohol |
Chemical Properties of Potassium Hexacyanoferrate (III)
- When potassium hexacyanoferrate (III) reacts with a strong acid, highly toxic hydrogen cyanide gas is evolved.
6H+ + [Fe(CN)6]3− → 6HCN + Fe3+
- Potassium ferrocyanide is obtained when potassium hexacyanoferrate (III) reacts with potassium hydroxide.
4KOH + 4K3[Fe(CN)6] → 2H2O + O2 + 4K4[Fe(CN)6]
- When potassium hexacyanoferrate (III) reacts with water, potassium monopentacyanoferrate and potassium cyanide are produced, and this reaction takes place in a boiling solution.
K3[Fe(CN)6] + H2O → K2[Fe(H2O)(CN)5] + KCN
- When potassium hexacyanoferrate (III) reacts with iron (III) chloride, iron (III) hexacyanoferrate (III) and potassium chloride are produced.
K3[Fe(CN)6] + FeCl3 → Fe[Fe(CN)6] + 3KCl
- When potassium hexacyanoferrate (III) reacts with freshly prepared iron (II) sulfate solution, a dark blue precipitate called Turnbull’s blue is produced.
4K3[Fe(CN)6] + 3FeSO4 → Fe4[Fe(CN)6]3 + 3K2SO4 + 6KCN
- When potassium hexacyanoferrate (III) reacts with lead (II) hydroxide and a diluted solution of potassium hydroxide, potassium hexacyanoferrate (II), lead (IV) oxide, and water are produced.
2K3[Fe(CN)6] + 2KOH + Pb(OH)2 → 2K4[Fe(CN)6] + PbO2 + 2H2O
Uses of Potassium Hexacyanoferrate III
- This compound is used as a mild oxidizing agent in organic chemistry.
- It is used in calico printing and wool dyeing.
- It is also used to harden iron and steel.
- It is used as a laboratory reagent and in electroplating.
- Potassium ferricyanide is widely used in photography and blueprint drawing.
- It is used to formulate Murakami’s etchant, which is used by metallographers. Murakami’s etchant is formed when potassium hexacyanoferrate III is mixed with potassium hydroxide (or sodium hydroxide as a substitute) and water.
Health Hazards of Potassium Hexacyanoferrate (III)
- Potassium hexacyanoferrate III is harmful if swallowed or inhaled.
- Potassium hexacyanoferrate III is low toxic but causes mild irritation to the eyes, skin, and respiratory tract.
- Potassium hexacyanoferrate III upon heating emits irritating or toxic fumes.
FAQs on Potassium Hexacyanoferrate (III)
Question 1: How is Potassium hexacyanoferrate (III) prepared?
Answer:
When chlorine is passed through a solution of potassium ferrocyanide, potassium Hexacyanoferrate (III) is produced.
2K4[Fe(CN)6] + Cl2 → 2K3[Fe(CN)6] + 2KCl
Question 2: What happens when Potassium hexacyanoferrate (III) reacts with water?
Answer:
When potassium hexacyanoferrate (III) reacts with water, potassium monoaquapentacyanoferrate and potassium cyanide are produced, and this reaction takes place in a boiling solution.
K3[Fe(CN)6] + H2O → K2[Fe(H2O)(CN)5] + KCN
Question 3: What are the uses of Potassium hexacyanoferrate (III)?
Answer:
This compound is used as a mild oxidizing agent in organic chemistry. It is used in calico printing and wool dyeing. It is also used to harden iron and steel. It is used as a laboratory reagent and in electroplating. Potassium ferricyanide is widely used in photography and blueprint drawing.
Question 4: What is the molecular weight of Potassium hexacyanoferrate (III)?
Answer:
Molecular formula of Potassium Hexacyanoferrate (III) is K3[Fe(CN)6]
Atomic mass of Potassium atom = 39.0983
Atomic mass of Iron = 55.845
Atomic mass of carbon atom = 12.011
Atomic mass of Nitrogen atom = 14.0067Molar mass = (3 × 39.0983) + 55.845 + (6 × 12.011) + (6 × 14.0067)
= 117.2949 + 55.845 + 72.066 + 84.0402
= 329.2461Hence, the molecular weight of Potassium Hexacyanoferrate (III) is 329.2461 g/mol.
Question 5: What happens when Potassium hexacyanoferrate (III) reacts with iron (II) sulfate solution?
Answer:
When potassium hexacyanoferrate (III) reacts with freshly prepared iron (II) sulfate solution, a dark blue precipitate called Turnbull’s blue is produced.
4K3[Fe(CN)6] + 3FeSO4 → Fe4[Fe(CN)6]3 + 3K2SO4 + 6KCN
Question 6: What are the hazards of Potassium hexacyanoferrate (III)?
Answer:
Potassium hexacyanoferrate (III) is harmful if swallowed or inhaled. It has low toxicity but causes mild irritation to the eyes, skin, and respiratory tract. Upon heating, it emits irritating or toxic fumes.