Potassium Permanganate (Kmno4)

Physical and Chemical Properties of Potassium Permanganate


Potassium Permanganate is also known as permanganate of potash or Condy’s crystals. It is a chemical compound with the chemical formula of KMnO4. It is made of a potassium (K+) ion and permanganate (MnO4-) ion. It is a strong oxidizing agent, so it readily takes and accepts electrons from other substances.

The physical shape of potassium permanganate is an odourless solid and they are dark purple in colour or bronze-coloured crystals. If these crystals are dissolved in water, the solution becomes purple in colour. Potassium permanganate can oxidize many substances, so it is very well known as the strong oxidizing agent.

The other names of potassium permanganate are chameleon mineral, Condy’s crystals, permanganate of potash, and hypermangan. The crystal structure of potassium permanganate is called orthorhombic.

The formula and structure:

KMnO4 is the chemical formula of potassium permanganate and 158.034 g/mol is the molar mass. Potassium permanganate is an ionic compound poised of potassium cation (K+) and the permanganate anion (MnO4-), in which the manganese atom is attached to four oxygen atoms through one single bond and three double bonds. The manganese metal is in the +7-oxidation state in this salt. Solid KMnO4 has an orthorhombic crystal structure.

The physical properties of potassium permanganate:

  • • Potassium permanganate is found as a bright purple coloured crystalline solid.

  • • It is odourless and has a density of 2.70 g/ml.

  • • The Melting point of potassium permanganate is 240 degree Celsius.

  • • It is available commercially as crystals, powder or tablets.

  • • It is soluble in water, acetone, acetic acid, methanol, and pyridine.

  • • It gets dissolved in ethanol and inorganic solvents.

  • The chemical properties of potassium permanganate:

  • • It gets readily dissolved in water to give a characteristic bright purple, dark pink or magenta coloured solution.

  • • It is a strong oxidizer that stains most organic materials that meet it, due to the formation of a dark brown reduced product MnO2.

  • • It is stable at normal circumstances but decomposes upon heating to give MnO2.

  • • Solid KMnO4 reacts violently with concentrated sulphuric acid, glycerol, and some simple alcohols.

  • Preparation of Potassium Permanganate:

    Potassium Permanganate is prepared from the mineral pyrolusite (MnO2). The preparation involves the following steps:

  • • Conversion of MnO2 to Potassium Manganate:

  • The powdered pyrolusite is combined with potassium hydroxide in presence of air to form potassium manganate, which is a green coloured compound.

    2MnO₂+ 4KOH+ O₂------->2K₂MnO₄ + 2H₂O 

  • • Oxidation of potassium Manganate to Potassium Permanganate:

  • Oxidation can be done in two methods. They are chemical oxidation and electrolytic oxidation.

    Chemical oxidation process:

    In this process, Potassium Manganate is treated with chlorine or ozone to form Potassium Permanganate.

    2K₂MnO₄+ Cl₂ 2KMnO₄ + 2KCl

    2K₂MnO₄ + H₂O + O₃ 2KMnO₄ + 2KOH + O₂

    Electrolytic oxidation process:

    In this process, potassium manganate solution is electrolyzed.

    K₂MnO₄ ↔ 2K⁺ + MnO²₄-

    H₂O ↔ H⁺ + OH-

    In this process, manganate ions are transformed into permanganate

    MnO²₄- (green) MnO⁻₄ + e⁻ (purple)

    After the oxidation process, the green colour solution transforms into a purple colour solution which is concentrated by evaporation and forms crystals on cooling.

    2KMnO₄→K₂MnO₄ + MnO₂ + O₂

    Organic and analytical:

    In Organic and Analytical labs, potassium permanganate is a very valuable reagent. In organic labs, it is used to synthesize and react with different organic compounds. In analytical labs, potassium permanganate is used to find out the amount of material that can be oxidized in a chemical sample, and the amount is referred to as the permanganate value.

    For example, it is used to find the kappa number, or the estimate of how much chemicals need to be used to bleach wood pulp, the fibrous material when fibres of wood are separated and later made into paper.

    Uses of Potassium Permanganate:

    Potassium Permanganate is a compound that can either easily transfer oxygen atoms to another compound or readily receive them from another compound. Both oxidation process namely the chemical and electrolytic oxidation change the properties of the original compound interacting with potassium permanganate.

    Potassium permanganate oxidizing ability gives it disinfectant, deodorizing, and cleansing properties that make it useful in several ways.

    Medical uses of Potassium Permanganate:

    Potassium permanganate sounds more like a confection that a highly caustic chemical used to treat infections. It is sold by prescription only. When it is mixed into liquid form, it is used to treat skin conditions, fungal infections, and ulcers.

    Skin infections:

    Potassium Permanganate treats a lot of skin infections, including canker sores, dermatitis, eczema, vaginal thrush, acne, and vulvovaginitis. When spread to small, wet wounds, only a small amount of a very dilute solution or liquid is necessary. Larger areas such as infected eczema on large areas of the body, predominantly in the presence of blisters, oozing or pus, may require cure with potassium permanganate water baths. These baths must contain very less potassium permanganate solution. The strength or dilution is essential as potassium permanganate crystals and concentrated solutions burn skin. Even dilute solutions can irritate skin and frequent use may cause burns.

    Wound cleaning:

    Potassium Permanganate wet dip treat blistering wounds such as ulcers and abscesses. The severe action dries out blisters, preparing them for further treatment. The broad antimicrobial properties kill bacteria, algae, and viruses at varying concentrations, decreasing the likelihood for secondary wound infections.

    Fungal infections:

    It treats fungal infections such as athlete’s foot. Symptoms of these conditions include itching or burning, usually between the toes, as well as redness or a scaly skin appearance related with to feeling as if the foot is on fire. These symptoms are relieved by killing the growth of the fungus using the oxidizing action of potassium permanganate. The affected foot is dipped in a solution of potassium permanganate dissolved in water for about 15 minutes twice a day for two to three weeks. One side effect of this treatment is that the foot will temporarily turn brown from the potassium permanganate.

    Hair dye allergies:

    Most commercially available permanent hair dyes contain a non-oxidized dye that is mixed with a developer or oxidizer. The oxidizer breaks down the natural hair pigment melanin, then the dye replaces the melanin. Limited reactions of this dye with the oxidizer may cause an allergic reaction. Dilute solutions of potassium permanganate are applied as a compress to the affected area in order to relieve the symptoms by fully oxidizing the dye when an allergic reaction occurs.

    Drinking water treatment of potassium permanganate in a well:

    Potassium permanganate is a point of entry treatment methods that oxidizes dissolved manganese, and hydrogen sulphide and iron into solid elements that are filtered out of the water. It can also be used to control iron bacteria growth in water.
    Potassium permanganate is available as a purplish solid and dry. A device will inject the solution of potassium permanganate into the water between the water pump and water holding tank.

    Potassium permanganate oxidizes iron, manganese, hydrogen sulphide into particles. The particles are then filtered with a multimedia filter which can be either manganese-coated aluminium silicate above manganese-treated green sand or an 8-inch layer of anthracite above manganese-treated green sand.

    If an insufficient amount of iron, manganese or hydrogen sulphide is oxidized prior to filtration, the manganese coating on the filter area acts as a backup oxidant to treat any remaining contaminant. If too much KMnO4 is fed into the water prior to filtration, the excess potassium permanganate serves as a regenerate for the filter area. When it leaves the filter, the water must be colourless.

    Hazardousness of potassium permanganate:

  • • Potassium permanganate can affect the breath when inhaled in.

  • • Contact of potassium permanganate can severely irritate the nose and throat.

  • • It can also irritate the lungs causing cough or shortness of breath. It can also affect the liver and kidney.

  • • It may decrease fertility.

  • • It stains skin and clothing and should be handled with care.

  • Other miscellaneous uses of potassium permanganate:

  • • Solutions of potassium permanganate are used together with 80% hydrogen peroxide to propel a rocket. In this, it was called Z-stoff. This propellant is still used in torpedoes.

  • • A dilute of 10mg/l of potassium permanganate can be used to eliminate snails from plants prior to placing them in a freshwater aquarium.

  • • High-grade potassium permanganate can be found at pool supply stores and is used in rural areas to eliminate hydrogen sulphide and iron from well water.

  • • Potassium permanganate is also used in survival kits along with either glycerine or a glucose tablet for making fire. The glucose tablet can be powdered and mixed with potassium permanganate and it will burn if rubbed. It can also purify water and wounds, so it is useful in a survival kit.

  • • It is employed to treat some parasite diseases in fish, treatment of drinking water, as well as an antidote in phosphorus poisoning.

  • A small experiment using potassium permanganate:

    Take a small pile of potassium permanganate crystals and let one drop of glycerine fall in. More popularly known as glycerol, this is a thick, clear, sweet tasting compound used in the food industry. Soon after dripping the glycerine on to the crystals, acrid smell and a waft of smoke will arise before the liquid bursts into flame, powerfully oxidized by the potassium permanganate.