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Potassium Permanganate (KMnO4)

Potassium Permanganate which is also commonly referred to as KMnO4 is a chemical compound that is used in many industries for its oxidizing functionality. This compound is also sold commercially mostly for medicinal purposes. It is available as crystals, powder, and tablets. While this is one of the most discussed topics in Chemistry we will understand everything about the compound in detail below.

Potassium Permanganate formula is written as KMnO4. This inorganic compound belongs to the category of salt and consists of two ions namely K+ and MnO-4 ions. Some of its key properties include its oxidizing and solubility properties. KMnO4 is a strong oxidizing agent and most of its uses are based on this property. It is also easily soluble in water and usually forms a pinkish or purple solution when potassium permanganate is in water. Below we will talk more comprehensively about this chemical compound.

IUPAC Name Potassium Permanganate
Chemical Formula KMnO4
Molar Mass 158.034 g/mol
Density 2.7 g/cm3
Melting Point 240 °C (464 °F; 513 K)

Discovery Of KMNO4

The traces of KMnO4 was first found when a Germa-Dutch chemist named Johann Rudolf Glauber started his experiments by mixing two compounds namely pyrolusite which is a mineral consisting of manganese dioxide and potassium carbonate. He dissolved the mixture in water which led to the formation of a green solution. This was potassium manganate. Interestingly, the colour of the solution slowly changed from blue to violet and red. This experiment represented the first production of KMnO4.

A more prominent discovery was made by a chemist from London, Henry Bollmann Condy. In his case, he fused pyrolusite with sodium hydroxide (NaOH) and dissolved it in water. This led to the production of a solution with several characteristics and the primary one was the disinfectant property. The solution was patented and used commercially. It was known as ‘Condy’s Fluid’. However, there was one drawback as the solution was found to be unstable. This defect was corrected with the use of potassium hydroxide (KOH) instead of NaOH. Moreover, potassium permanganate crystals could now be obtained from the solution. Later, these crystals were known as ‘Condy’s powder’ or ‘Condy’s crystals’.

Preparation Of KMnO4

Industrially, KMnO4 is prepared using manganese dioxide. As stated above, this chemical compound is reacted with alkali metal hydroxide which is potassium hydroxide. The mixture is then heated in the air at high temperatures. When the reaction is completed potassium manganate is formed.

2 MnO2 + 4 KOH + O2 → 2 K2MnO4 + 2 H2O

After the formation of potassium manganate, it goes under electrolytic oxidation in alkaline media to form permanganate.

2 K2MnO4 + 2 H2O → 2 KMnO4 + 2 KOH + H2

Alternatively, potassium permanganate can also be formed using a chemical oxidation process. It involves treating potassium manganate either with ozone or chlorine. K2MnO4 is oxidized to KMnO4 by bubbling CO2 or Cl2 or ozone.

3K2MnO4 + 2CO2 → 2KMnO4 + MnO2 + 2K2CO3

KMnO4 Structure

When KMnO4 is in solid-state it has an orthorhombic crystal structure where each MnO4 centres are arranged in a tetrahedral geometry.

KMnO4 Structure

Potassium Permanganate Properties

We will look at the physical and chemical properties of KMnO4 below.

Physical Properties

  • KMnO4 is usually in the form of a crystalline solid.
  • It is odourless.
  • KMnO4 colour is described to be purple or magenta.
  • KMnO4 molar mass is 158.034 g/mol.
  • It has a density of 2.7 g/cm3.
  • It’s melting point is 240 °C (464 °F; 513 K).

Chemical Properties

  • KMnO4 has high solubility and easily dissolves in water.
  • It acts as a strong oxidizing agent.
  • It can react violently with concentrated acids such as sulphuric acid and various alcohols. It can even produce fire when reacted with substances like glycerin.

KMnO4 Reactions

KMnO4 can be used to oxidize a lot of organic compounds. It can also be used to oxidize carbon atoms mostly with weak bonds. It can react with alcohols, alkenes, aldehydes, alkynes and aromatic side chains.

  • Aldehydes are generally oxidized to carboxylic acids.
  • Alcohols are oxidized to carbonyls.
  • Potassium permanganate can be used to oxidize alkenes to glycols.
  • In alkynes, there is a formation of diones.

KMnO4 Uses

Potassium permanganate uses are mostly centred around its oxidizing property. It is also used widely because there is no generation of toxic byproducts.

  1. KMnO4 is used extensively as an antiseptic to treat different kinds of fungal infections, ulcers, wounds and other skin conditions.
  2. It is used in water treatment mainly to remove minerals such as iron and hydrogen sulfide and control organisms such as zebra mussels.
  3. This chemical compound is also used to remove rust that may be found in water pipes and equipment.
  4. Another major use of potassium permanganate is in the synthesis of organic compounds.
  5. It is used in the preservation of fruits.
  6. It is found in survival kits. It can be used to start a fire easily.
  7. It is also used in rocket propellant.
  8. KMnO4 is used in treating fish diseases and parasites.

Adverse Effects Of KMnO4

We will understand some adverse effects of KMnO4. Normally the concentrated solution of potassium permanganate is usually corrosive in nature. It can cause irritation and burns on the skin as well as damage to the membranes in the eyes, throat, nose, etc. It also leaves a coloured stain on the skin and nails. Ingestion of potassium permanganate can lead to abdominal pain, vomiting, burns in the throat, shortness of breath, cardiovascular collapse, kidney damage and ultimately death.

Frequently Asked Questions – FAQs

What are the uses of potassium permanganate?

Potassium permanganate is used in water treatment to remove iron and hydrogen sulfide. It is used to keep water free from bacteria. It is also used as an oxidizing agent in organic reactions.

How is KMnO4 prepared?

2MnO2 + 4KOH + O2 → 2K2MnO4 + 2H2O
2K2MnO4 + 4HCl → 2KMnO4 + MnO2 + H2O + 4KCl

What are the dangers of potassium permanganate?

Potassium Permanganate causes irritation in the throat and nose on inhalation.

What is the molecular mass of potassium permanganate?

The molecular mass of potassium permanganate is 158 g/mol.

What happens when ethene reacts with KMnO4?

Ethene on reaction with KMnO4 gives ethylene glycol.
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