KMnO4 - Potassium Permanganate

Potassium permanganate is a versatile purple coloured chemical compound. It is a potassium salt of manganic acid. Also known as the permanganate of potash, it has many other names such as chameleon mineral, Condy’s crystals and hypermangan. Potassium permanganate was produced for the first time by German chemist Johann Rudolf Glauber in 1659 but was soon forgotten. It was rediscovered by British chemist Henry Condy, who manufactured disinfectants known as 'Condy's crystals', potassium permanganate became a big success. It has oxidising properties so it has found varied use in the medical and chemical industry. Its chemical formula is KMnO4.

Potassium Permanganate Structure – KMnO4

• Potassium permanganate is an ionic compound consisting of a potassium cation (K+) and permanganate anion (MnO4-).

• In permanganate anion (MnO4-) the manganese atom is bonded with four oxygen atoms through three double bonds and one single bond. The oxidation state of manganese in this salt is +7.

• The crystal structure of solid KMnO4 is orthorhombic. Each MnO4- structure is present in a tetrahedral geometry.

Physical Properties of Potassium Permanganate – KMnO4

• It is a bright purple or bronze coloured chemical compound.

• It has a density of 2.7g/ml and its molar mass is 158.034g/mol.

• The compound is odourless i.e. it has no smell but has a sweet taste.

• It has a high melting point of 2400 C.

• It is mostly found in powder, crystal or in tablet form.                                  

Chemical Properties of Potassium Permanganate

• Potassium permanganate is soluble in acetone, water, pyridine, methanol and acetic acid. It is also readily soluble in inorganic solvents.

• It has a rich purple colour in concentrated solution and pink colour in dilute solution.

• It is not combustible but supports the combustion of other substances.

• Under normal conditions, it is a highly stable compound but decomposes upon heating to form MnO2 and liberates oxygen.

             2KMnO4  \[ \overset{\bigtriangleup}{\rightarrow} \]  K2MnO4 + MnO2 + O2 

• It is a strong oxidising agent (a compound that can easily transfer its oxygen to other substances) forming a dark brown coloured manganese dioxide (MnO2) which stains anything that is organic. It can readily accept electrons from other substances.

• It reacts violently with sulphuric acid resulting in an explosion.

• It reacts immediately with glycerol and simple alcohols producing flame and smoke.

Reactions of Potassium Permanganate (KMnO4)

Most of the reactions with Potassium Permanganate are redox reactions (a chemical reaction in which one substance is oxidised and another is reduced). KMnO4 can oxidise many inorganic compounds. The medium of solution plays an important role in determining the products of the reaction.

• In the acid medium, manganese is reduced to Mn2+. 

 2KMnO4+ 5Na2SO3 + 3H2SO4 🡪 2MnSO4 + 5Na2SO₄ + K2SO4 + 3H2O 

• In a neutral medium, MnO2 forms a brown deposit.

   2KMnO4 + 3K2SO3 + H2O 🡪 3K2SO4+2MnO2 + 2KOH 

• In the alkaline medium, MnO42- is reduced. 

2KMNO4+ Na2SO3 + 2KOH 🡪 2K2MnO4 + Na2SO4 +     H2O

• On heating, permanganate crystals decompose to release oxygen.

2KMnO4 ∆→  K2MnO4 + MnO2 + O2

• On diluting permanganate crystals in the presence of direct sunlight, oxygen is liberated.

4KMnO4 + 2H2O Sunlight→ 4KOH + 4MnO2 + 3O2

• Other reactions of potassium permanganate are as follows:

With sulphuric acid:

2KMnO4+ H2SO4 🡪 Mn2O7 + K2SO₄ + H2O 

With hydrogen peroxide:

2KMnO4 + 3H2O2🡪 2KOH + 2MnO2 + 3O2+ 2H2O 

• It can also oxidise carbon atoms that have double bonds in weak alkaline or neutral medium.

СН2=СН2 + 2KMnO4+ 2H2O 🡪 CH2OH–CH2OH + 2MnO2 + 2KOH (with cooling).

• It can oxidise aldehydes to form carboxylic acids.

• It oxidises alcohol to form carbonyls.

• It can also oxidise carbon atoms that have triple bonds to form ions.

• It oxidises sugar to acids by breaking the carbon skeleton into double bonds.

Uses of Potassium Permanganate (KMnO4)

Medical uses

• Potassium permanganate acts as a disinfectant Due to its oxidising property, it can act as a disinfectant to treat skin infections such as dermtitis, canker sores, ulcers, eczema and fungal infections. When applied to small wounds, it attacks the outer cell membrane of the microorganism, thereby, oxidising it and destroying its structure. In some cases of large wounds, doctors advise potassium permanganate water baths with dilute solutions. Care must be taken as overuse of this chemical may cause irritation and burns.

• It can be used to clean wounds. Wet wounds like ulcers and abscesses can be cleaned with potassium permanganate solution. This treatment kills the microbes and prevents secondary infection. It also helps in drying out the blisters.

• It is very effective in treating a fungal infection called athlete’s foot. The oxidising action of permanganate solution kills the fungus thereby relieving the symptoms such as itching and burning sensation.

• It can also be used to treat allergies due to reactions to commercial hair dyes. Dyes contain an oxidizer that breaks down the melanin pigment in hair and allows for the dye to penetrate. Due to the incomplete action of dye and oxidizer sometimes there is an allergic reaction that causes discomfort and itchiness. Permanganate solution is applied in such a case as a compress to relieve the symptoms and to completely oxidise the dye.

Water treatment

• It is used in water treatment plants to kill contaminants and also to remove foul smells from water. It oxidises iron, hydrogen sulphide and manganese into solid particles which are then removed by filtration. The treatment does not produce any toxic substance so it is very safe for use.

• It can also be used to clean water in swimming pools.

Analytical and organic chemistry

Due to its strong colour and oxidising nature, potassium permanganate is used in chemistry labs as a reagent to calculate the amount of substance that can be oxidised in a sample. This value is referred to as the permanganate value.  

In the paper-making industry, the kappa number (amount of standard permanganate solution consumed by wood pulp) is used to find out the amount of chemical needed to bleach the pulp. Inorganic chemistry labs it is often used in reactions with organic compounds.

Other uses

• When mixed with 80% hydrogen sulphide it acts as a propellant for rockets and torpedoes.

• In rural areas, it is used to remove iron and hydrogen sulphide from well water.

• It can also help to remove rust from water pipes. 

• It can be used to remove snails from plants before being transferred to an aquarium.

• It is an important component in survival kits along with glycerine/ glucose tablets where it can come in handy in creating fire. By rubbing glucose tablets with permanganate powder, fire can be started. It can also be used to clean water and clean wounds.

• It can be used as an antidote in case of phosphorus poisoning.

• It is often used to treat parasite infections in fish.

Effects on Health

KMnO4 is a hazardous chemical as even short term exposure may cause discomfort. By following personal hygiene and taking proper precautions in handling potassium permanganate one can avoid health hazards. Some of its effects on health are as follows:

• Concentrated KMnO4 causes irritation to the skin and eyes. Long term exposure may damage the eyes permanently.

• If inhaled, it can cause irritation to the nose and throat. Even the lungs may be affected causing coughing, shortness of breath and pulmonary oedema (buildup of fluids in lungs).

• KMnO4 may also affect the liver and kidneys.

• Long term exposure may affect fertility.

Hence article is very important to understand the chemical potassium permanganate. All the necessary details of KMnO4 is provided here such as its physical, chemical properties, reactions, uses and effects on health.