Potassium Permanganate: Discovery, Preparation, Properties

Potassium Permanganate is a dark purple coloured substance having the chemical formula of \({\rm{KMn}}{{\rm{O}}_4}\) and is usually referred to or used for its excellent oxidising property. Potassium permanganate is present in the markets as it is a disinfectant and used for medicinal purposes. Also, \({\rm{KMn}}{{\rm{O}}_4}\) is readily available in the form of tablets, crystals or powder in the market.

Potassium permanganate is used as a medicine for many skin conditions. These include fungal infections of the foot, impetigo, pemphigus, superficial wounds, dermatitis and tropical ulcers. It is used with procaine benzylpenicillin for tropical ulcers. It is commonly used in skin conditions that produce too much fluid. It can be applied as a soaking dressing or bath. This article will discuss its uses, its preparation and many other minor attributes attached to it.

Discovery of Potassium Permanganate

German-Dutch alchemist called Johann Rudolf Glauber 1659 discovered Potassium permanganate. As an alchemist, He mixed two minerals, pyrolusite and potassium carbonate. Pyrolusite is a mineral of manganese\(\left( {{\rm{Mn}}{{\rm{O}}_2}} \right)\), and Potassium carbonate is \({{\rm{K}}_2}{\rm{C}}{{\rm{O}}_3}.\) He obtained a substance from mixing them, which, when dissolved in water, gives green colour at first, leading to purple colour and ending on a red colour solution. Hence, indicating the formation of Potassium permanganate.

In the 1800s, British scientist Henry Bollmann Condy working on disinfectants, also found a way to produce \({\rm{KMn}}{{\rm{O}}_4}\) with the help of the same pyrolusite mineral and Sodium hydroxide. When Henry heated the pyrolusite, sodium hydroxide mixture and added water to it, the combination produced \({\rm{KMn}}{{\rm{O}}_4}.\) This solution had disinfectant qualities but was not entirely stable.

So he stabilised the solution by adding Potassium hydroxide instead of sodium hydroxide in the making and patented the method to prepare Potassium permanganate. He named this solution “Condy’s Fluid” and its crystalline form as “Condy’s Crystal”.

Learn About Potassium Permanganate

Structure of KMnO₄

Potassium permanganate is an ionic compound consisting of a potassium cation and a permanganate anion. The manganese atom in the permanganate ion is bonded to \(4\) oxygen atoms through three double bonds and one single bond, as shown in the below picture.

Preparation of Potassium Permanganate

As was done years back, now also Potassium permanganate is prepared with the help of pyrolusite which is \({\rm{Mn}}{{\rm{O}}_2}\) and reacting it with various types of chemical reagents. Usually, \({\rm{KMn}}{{\rm{O}}_4}\) is prepared in two steps:

1. Converting the pyrolusite into potassium manganate.
2. Converting the obtained potassium manganate into \({\rm{KMn}}{{\rm{O}}_4}\).

Let us study the process

A. The conversion of pyrolusite mineral\(\left( {{\rm{Mn}}{{\rm{O}}_2}} \right)\) into potassium manganate: The conversion of pyrolusite into the green coloured potassium manganate is done by reacting the pulverised or powdered mineral with potassium hydroxide or potassium carbonate in the presence of air, i.e.,  in the presence of oxygen or some powerful oxidising agent like potassium nitrate or potassium chlorate

\({\rm{2Mn}}{{\rm{O}}_2} + 4{\rm{KOH}} + {{\rm{O}}_2} \to 2{{\rm{K}}_2}{\rm{Mn}}{{\rm{O}}_4} + 2{{\rm{H}}_2}{\rm{O}}\)
\(2{\rm{Mn}}{{\rm{O}}_2} + 2{{\rm{K}}_2}{\rm{C}}{{\rm{O}}_3} + {{\rm{O}}_2} \to 2{{\rm{K}}_2}{\rm{Mn}}{{\rm{O}}_4} + {\rm{2C}}{{\rm{O}}_2}\)
\({\rm{Mn}}{{\rm{O}}_2} + 2{\rm{KOH}} + {\rm{KN}}{{\rm{O}}_3} \to {{\rm{K}}_2}{\rm{Mn}}{{\rm{O}}_4} + {\rm{KN}}{{\rm{O}}_2} + 2{{\rm{H}}_2}{\rm{O}}\)
\({\rm{3Mn}}{{\rm{O}}_2} + 6{\rm{KOH}} + {\rm{KCl}}{{\rm{O}}_3} \to 3{{\rm{K}}_2}{\rm{Mn}}{{\rm{O}}_4} + {\rm{KCl}} + 2{{\rm{H}}_2}{\rm{O}}\)

The same potassium manganate obtained in this reaction shows the disproportionation reaction to convert into potassium permanganate if allowed to stay in a neutral or acidic solution for an extended period.

\(3{\rm{MnO}}_4^{2 – } + 4{{\rm{H}}^ + } \to 2{\rm{MnO}}_4^ – + {\rm{Mn}}{{\rm{O}}_2} + 2{{\rm{H}}_2}{\rm{O}}\)

B. The potassium manganate obtained from the above reaction is then treated with oxidising agents to convert it into potassium permanganate. The solution of Potassium manganate passed with the bubbles of gases like carbon dioxide, chlorine or ozonised oxygen gas. When passed through the green solution of potassium manganate, these gases convert it into a purple coloured solution of potassium permanganate.

\(3{{\rm{K}}_2}{\rm{Mn}}{{\rm{O}}_4} + 2{\rm{C}}{{\rm{O}}_2} \to 2{\rm{KMn}}{{\rm{O}}_4} + {\rm{Mn}}{{\rm{O}}_2} + 2{{\rm{K}}_2}{\rm{C}}{{\rm{O}}_3}\)
\({\rm{2}}{{\rm{K}}_2}{\rm{Mn}}{{\rm{O}}_4} + {\rm{C}}{{\rm{l}}_2} \to 2{\rm{KMn}}{{\rm{O}}_4} + 2{\rm{KCl}}\)
\({\rm{2}}{{\rm{K}}_2}{\rm{Mn}}{{\rm{O}}_4} + {{\rm{H}}_2}{\rm{O}} + {{\rm{O}}_3} \to 2{\rm{KMn}}{{\rm{O}}_4} + 2{\rm{KOH + }}{{\rm{O}}_2}\)

Amongst the given reactions, the reaction of potassium manganate with carbon dioxide is the most uneconomical as it is forming the pyrolusite mineral again in the reaction. The most economical reaction is the reaction of potassium manganate with chlorine gas as the by-product obtained disappears during the reaction.

Properties of Potassium Permanganate

The properties of potassium permanganate are particular and are essential for the field of chemistry.:

A. Physical Properties 

1. The colour of potassium permanganate is precise and known, which is dark purple.

2. The solubility of potassium in water is excellent as it can allow \(76\,{\rm{g}}\) of potassium permanganate into \(1\) litre of water at \(25^\circ \,{\rm{C}}.\)

3. Potassium permanganate has a melting point of \(513\,{\rm{K}}\left( {240^\circ \,{\rm{C}}} \right)\)

4. Potassium permanganate has a density of \(2.7\,{\rm{g/ml}}\)

Study About Preparation and Properties of Potassium

B. Chemical Properties

1. On heating, potassium permanganate gets decomposed into potassium manganate and manganese oxide with oxygen gas.

\(2{\rm{KMn}}{{\rm{O}}_4} \to {{\rm{K}}_2}{\rm{Mn}}{{\rm{O}}_4} + {\rm{Mn}}{{\rm{O}}_2} + {{\rm{O}}_2}\)

2. Potassium permanganate reacts with concentrated sulphuric acid to form \({\rm{M}}{{\rm{n}}_2}{{\rm{O}}_7}\) which on heating converts back into \({\rm{Mn}}{{\rm{O}}_2}\)

\(2{\rm{KMn}}{{\rm{O}}_4} + 2{{\rm{H}}_2}{\rm{S}}{{\rm{O}}_4} \to {\rm{M}}{{\rm{n}}_2}{{\rm{O}}_7} + 2{\rm{KHS}}{{\rm{O}}_4} + {{\rm{H}}_2}{\rm{O}}\)

\(2{\rm{M}}{{\rm{n}}_2}{{\rm{O}}_7} \to 4{\rm{Mn}}{{\rm{O}}_2} + 3{{\rm{O}}_2}\)

3. When potassium permanganate is heated in the presence of hydrogen gas, it forms caustic potash.

\(2{\rm{KMn}}{{\rm{O}}_4} + 5{{\rm{H}}_2} \to 2{\rm{KOH}} + 2{\rm{MnO}} + 4{{\rm{H}}_2}{\rm{O}}\)

4. The most important chemical property of Potassium permanganate is its oxidising property as it is an excellent oxidising agent. It also reacts differently depending on the nature of the medium in which it is present, in acidic, basic or neutral medium.

5. The aldehydes transform into carboxylic acids with the help of potassium permanganate as the oxidising agent.

6. The alkynes are converted into Dione(Carbon compounds having two ketone groups) in the presence of potassium permanganate.

Uses of Potassium Permanganate

As potassium permanganate reduces, it does not leave any toxic product, and due to this, it is used as an oxidising agent. Most of the uses of potassium permanganate revolve around its oxidising nature.

1. The potassium permanganate is used extensively for its antiseptic property and is used to treat ulcers, wounds and other skin infections like eczema.
2. Water may have minerals of iron and hydrogen sulphides which leaves a smell in the water. Adding potassium permanganate in water removes unwanted minerals.
3. As stated above, potassium permanganate is used to synthesise many organic compounds and is even used to identify saturated hydrocarbons.
4. Potassium permanganate helps in preserving fruits like bananas by removing ethylene around them.
5. Potassium permanganate can be used to initiate fires and is present in survival kits.

Side Effects of Potassium Permanganate

1. Side effects may include skin irritation and discolouration of clothing. Serious burns of a child have been reported from an insoluble pellet. For the treatment of eczema, it is recommended to use it for a few days at a time because of the potential for skin irritation. High concentration solutions can result in chemical burns. Therefore, the British National Formulary recommends that 100 mg be dissolved in one litre of water before use to make a 1:10,000 (0.01%) solution. It is not recommended to wrap dressings soaked in potassium permanganate.

2. It is considered very toxic if taken by mouth. Side effects may include nausea, vomiting, and shortness of breath. Death can occur if eaten in sufficient quantities (about 10 grams).

3. Concentrated solutions result in adult respiratory distress syndrome or inflammation of the airways when intoxicated. Gastroscopy is one of the recommended measures for those consuming potassium permanganate. Activated charcoal or drugs that cause vomiting are not recommended. While drugs such as ranitidine and N-acetylcysteine ​​can be used in poisoning, the evidence for this use is poor.

Can Potassium Permanganate Kill You?

Potassium permanganate is good to use for the outer body only and should not be consumed at all. If swallowed, it may lead to severe abdominal pain, vomit and burning sensations, burning in the throat, shortness of breath and may even cause cardiovascular collapse or failure in the kidney and can even cause death.

FAQs

Q.1. Why KMnO4 is a self-indicator?
Ans. The solution under titration loses its purple colour once all the permanganate ions are used up in the reaction, indicating the end of the reaction. Therefore, it is called a self-indicator. It serves as an indicator apart from being one of the reactants.

Q.2. What are the uses of Potassium Permanganate?
Ans. Potassium Permanganate is used extensively for its antiseptic property and is used to treat ulcers, wounds and other skin infections like eczema. It is used to purify water and preserve fruits like bananas by removing ethylene around them.

Q.3. What is the structure of Potassium Permanganate?
Ans. Potassium Permanganate is an ionic compound consisting of a potassium cation and a permanganate anion. The manganese atom in the permanganate ion is bonded to 4 oxygen atoms through three double bonds and one single bond.

Q.4. Can I drink Potassium permanganate?
Ans. Potassium Permanganate is good to use for the outer body only and should not be consumed at all. If swallowed, it may lead to severe abdominal pain, vomit and burning sensations, burning in the throat, shortness of breath and may even cause cardiovascular collapse or failure in the kidney and can even cause death.

Q.5. Why is KMnO4 used to purify water and can act as a disinfectant?
Ans. Water may have minerals of iron and hydrogen sulphides which leaves a smell in the water. These minerals can be removed from the water by adding potassium permanganate.

Q.6. How is potassium Permanganate prepared?
Ans. Potassium Permanganate is prepared with the help of pyrolusite which isMnO2, and reacting with various types of chemical reagents. Usually, the preparation of Potassium permanganate is done in two steps: converting the pyrolusite into potassium manganate and converting the obtained potassium manganate into potassium permanganate.

Now that you have a detailed article on Potassium Permanganate, we hope your preparation goes off well. If you have any query do let us know about them in the comment section below and we will get back to you soon.