Potassium Cyanide

How does potassium cyanide cause sudden death?

  • Potassium cyanide when consumed causes death by gradually arresting the supply of oxygen to our body’s cells by forming complexes with haemoglobin and cytochrome (a protein which helps in the respiration of cells), depriving them of their capacity to transport or exchange oxygen.
  • Normally, oxygen is carried to different parts of the body from the lungs by the blood using haemoglobin, which is the iron-containing, oxygen-carrying molecule of the red blood cells. 
  • Haemoglobin is made up of a globular protein and four heme groups. The iron (in ferrous state) present in these heme complexes can bond to either an oxygen molecule or a water molecule or exchange one for the other without much difficulty. It is because of this ability that haemoglobin is able to pick up oxygen from the lungs, carry it to the cells, and bring water in return.
  • Cells respire oxygen with the help of myoglobin (haemoglobin-like proteins present in the cells) and cytochrome, which carries electrons.
  • Specific forms of cytochrome and haemoglobin also cause sudden death when poisoned by cyanide.
    • When potassium cyanide is consumed, it splits into a potassium ion and a cyanide ion.
    • The cyanide ion has a greater affinity for the ferrous ion.
    • As a result it occupies the site meant for oxygen in haemoglobin. This process is irreversible and prevents the transfer of oxygen.
  • One form of cytochrome, designated cytochrome-a, also binds with the cyanide ion and stabilises the iron to such an extent that it does not take part in the electron transfer to the cell. This prevents oxygen intake by the cell.
  • The symptoms of cyanide poisoning are giddiness, headache, and bluish tinge of the skin. If not treated immediately, unconsciousness and death will follow. 
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Potassium Cyanide:

  • It is a compound with the formula KCN.
  • It is characterized as a white crystalline solid. 
  • Potassium cyanide is highly soluble in water.
  • It is a reducing agent and reacts with acids of all kinds to generate poisonous hydrogen cyanide gas. 
    • A reducing agent (also known as a reductant, reducer, or electron donor) is a chemical species that “donates” an electron to an electron recipient (called the oxidizing agent or electron acceptor).
  • KCN is produced by treating hydrogen cyanide with an aqueous solution of potassium hydroxide, followed by evaporation of the solution in a vacuum: HCN + KOH → KCN + H2O.
  • Potassium cyanide is highly toxic, and a dose of 200 to 300 milligrams will kill nearly any human.


  • Most KCN is used in gold mining, organic synthesis, and electroplating.
  • KCN is widely used in organic synthesis for the preparation of nitriles and carboxylic acids.
  • It also finds use for the synthesis of hydantoins, which can be useful synthetic intermediate. 
  • Within the chemicals industry, potassium cyanide is most often used to help prepare chemicals for use in sectors such as manufacturing, pharmaceutical, and plastics. It is a powerful reagent for which the applications are growing alongside the demand for industrially manufactured products.
  • KCN is used as a photographic fixer in the wet plate collodion process.
    • The KCN dissolves silver where it has not been made insoluble by the developer.
    • This reveals and stabilizes the image, making it no longer sensitive to light.
    • Modern wet plate photographers may prefer less toxic fixers, often opting for sodium thiosulfate, but KCN is still used.
    • In the 19th century, cyanogen soap, a preparation containing potassium cyanide, was used by photographers to remove silver stains from their hands.

Prelims Previous Year Question (2015): 

Q. Brominated flame retardants are used in many household products like mattresses and upholstery.

Why is there some concern about their use?

1. They are highly resistant to degradation in the environment.

2. They are able to accumulate in humans and animals.

Select the correct answer using the code given below.

(a) 1 only

(b) 2 only

(c) Both 1 and 2

(d) Neither 1 nor 2

Answer: (c)

Practice Question for Prelims 

Q. ‘Potassium Cyanide’ has applications in which of the following?

    1. Electroplating
    1. Used as a photographic fixer
    1. Gold Mining
    1. Fire extinguishing agent
    1. Pharmaceutical sectors

Select the correct answer using the code given below:

(a) 1, 2 and 3 only

(b) 1, 2, 3 and 5 only

(c) 1, 2, 3 and 4 only

(d) 2, 3, 4 and 5 only

Answer: (b)


    • Potassium Cyanide is non-combustible but forms flammable gas on contact with water or damp air.
    • The agent itself does not burn, but it may decompose upon heating to produce corrosive and/or toxic fumes.
  • Potassium cyanide releases highly flammable and toxic hydrogen cyanide gas on contact with water or damp air and in a fire.
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