Potassium permanganate is a purple-coloured crystalline salt that has important industrial, laboratory and medical applications.
It’s also commonly known as chameleon mineral, Condy’s crystals, permanganate of potash, although its IUPAC name is potassium manganate(VII).
The discovery of potassium permanganate can be traced back to Rudolf Glauber who, in 1659, produced potassium manganate (K2MnO4) from the mixture of pyrolusite (manganese dioxide) and potassium carbonate. The solution turns green when dissolved in water, which then gradually becomes violet and finally turns red. This was the first description of the chemical production of potassium permanganate. Refer to the balanced chemical equations below.
Initial reaction between manganese dioxide and potassium carbonate:
MnO2 + K2CO3 → K2MnO4
Secondary reaction when potassium manganate is dissolved in water:
3 K2MnO4 + 2 H2O → 2 KMnO4 + 4 KOH
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What is potassium permanganate used for?
Potassium permanganate is a strong oxidising agent that doesn’t produce toxic byproducts, making it useful for a variety of applications.
One of the first commercially available disinfectant products was popularised by the chemist and industrialist Henry Bollmann Condy in the late 19th century and early 20th century. His eponymous Condy’s crystals were effective in killing bacteria and fungi.
Potassium permanganate is used to treat a variety of skin conditions, such as fungal foot infections. It’s also used as a treatment for pemphigus (an auto-immune disease of the skin and mucus), superficial wounds, dermatitis, and tropical ulcers. Potassium permanganate is mainly applied topically on the skin.
One of the primary industrial applications of potassium permanganate is water treatment. It removes iron and hydrogen sulphide from water, thereby eliminating the rotten egg smell of factory wastewater.
Many commercially valuable organic compounds, such as medicines, require potassium permanganate to be synthesised. Some examples include ascorbic acid (vitamin C), chloramphenicol (antibiotic), saccharin (artificial sweetener), and isonicotinic acid (antibacterial drug for TB).
Potassium permanganate is also used in analytical chemistry. For example, it can help to determine the amount of organic material that can be oxidised in an aqueous solution. This is known as the permanganate value. This value is calculated through titration.
Fruits like bananas can easily become overripe and spoil as ethylene accumulates, which makes storing fruit a challenge. Potassium permanganate is used to oxidise the ethylene produced by such fruits and thus slow down the ripening process.
Potassium permanganate is often included in survival kits as it can be used to start fires and purify water.
Potassium permanganate formula
The chemical formula for potassium permanganate is KMnO4. The four oxygen atoms per molecule make the compound a good oxidising agent.
As you can see from this illustration, the permanganate group forms the negatively charged ion (anion) and the potassium forms the positively charged ion (cation). The permanganate is the one that oxidises.
Is potassium permanganate an antiseptic?
Being a strong oxidising agent makes potassium permanganate a good but mild antiseptic. It can kill bacteria and fungus by oxidising the cell membranes of microorganisms, which causes the membranes to rupture.
Consequently, it can dry the skin because of its astringent properties. Potassium permanganate can also be taken orally but in a very low concentration of just 0.01% or one part per ten thousand.
What are the dangers of potassium permanganate?
Despite its many medicinal properties, potassium permanganate is considered a hazardous substance in high concentrations. It can cause severe irritation and even burn the skin and eyes.
When inhaled, it can result in coughing and shortness of breath. High levels of exposure can even lead to pulmonary oedema (fluid build-up in the lungs), and damage the liver and kidneys.
Does potassium permanganate expire?
When tightly sealed, potassium permanganate has a shelf life of around five years. However, once you open the container, it will start to degrade and may only take about a year to expire.
The substance is relatively stable as long as it is not exposed to the open air, especially air with high humidity.
Is potassium permanganate harmful?
As previously mentioned, potassium permanganate can irritate the skin and damage the eyes. It also has harmful effects on the internal organs. It’s therefore important to avoid direct and concentrated exposure to the substance. Inhalation or ingestion can be particularly dangerous.
What are the applications of potassium permanganate in chemistry?
Potassium permanganate is particularly useful in analytical chemistry. It can be used to determine the permanganate value of a sample solution, which is the amount of organic material that can be oxidised. This is calculated through redox titration.
Potassium permanganate can also be used to calculate the kappa number of a wood pulp, which is an indication of its bleachability.
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