Chemical Bonding and Molecular Structure

KMnO4

Potassium permanganate is an inorganic compound. It has the chemical formula \(KMnO_4\) and composed of K+ and \(MnO_4^-\) i.e., potassium ion and permanganate ion respectively. Potassium permanganate is a purplish-black crystalline salt. This crystalline salt easily dissolves in water and gives intensely pink or purple solutions. Learn more about KMnO4 here.

KMnO4

Introduction to \(KMnO_4\)

Potassium permanganate is broadly in use in the chemical industry and laboratories. It is in use as a strong oxidizing agent, and as a medication for dermatitis, for cleaning wounds, and also for general disinfection. Potassium permanganate is on the WHO Model List of Essential Medicines. Potassium permanganate is one of the safest and effective medicines needed in a health system.

In the year 1659, A German-Dutch chemist Johann Rudolf Glauber was the first person to discover the production of potassium permanganate.

As if when potassium permanganate crystals are dissolved in water the solution becomes purple. Potassium permanganate is considered a strong oxidizing agent and does not give toxic by-products. Potassium permanganate is generally prepared from other minerals such as manganese oxide.

Preparation of \(KMno_4\) (Potassium Permanganate)

Potassium permanganate is made industrially from manganese dioxide. Manganese also occurs as the mineral pyrolusite. In 2000, worldwide production of potassium permanganate was 30,000 tonnes. The manganese dioxide is fused with potassium hydroxide and then heated in air or with another source of oxygen, such as potassium nitrate or potassium chlorate. This process results in potassium manganate.

\(2 MnO_2 + 4 KOH + O_2 \rightarrow  2 K_2MnO_4 + 2 H_2O\)

With sodium hydroxide, the end product is not sodium manganate but it is Mn(V) compound, this compound is one reason the potassium permanganate is more commonly in use than sodium permanganate.

The potassium manganate is then converted into permanganate. It is done by the process of electrolytic oxidation in alkaline media:

\(2 K_2MnO_4+ 2 H_2O \rightarrow  2 KMnO_4 + 2 KOH + H_2\)

Other Methods

Potassium manganate can be oxidized using chlorine or by disproportionation process under acid conditions. The chlorine oxidation reaction is as follows:

\(2 K_2MnO_4 + Cl_2 \rightarrow  2 KMnO_4 + 2 KCl\)

And the acid-induced in disproportionation reaction is:

\(3 K_2MnO_4 + 4 HCl \rightarrow  2 KMnO_4 + MnO_2 + 2 H_2O + 4 KCl\)

A weak acid like carbonic acid is fine for this reaction:

\(3 K_2MnO_4 + 2 CO_2 \rightarrow  2 KMnO_4 + 2 K_2CO_3 + MnO_2\)

Permanganate salts can also be made by treating a solution of \(Mn^{2+}\) ions with strong oxidants. Oxidants like lead dioxide that is \(PbO_2\), sodium bismuthate that is \(NaBiO_3\), or peroxydisulfate can be in use.

Properties of \(KMnO_4\)

  • Potassium permanganate is an odourless and purple to magenta crystalline solid. \(KMnO_4\) is soluble in water, acetone, acetic acid, methanol, and pyridine.
  • It easily dissolves in ethanol and organic solvents.
  • Potassium permanganate is in the form of monoclinic prisms that is almost opaque with a blue metallic lustre.
  • Potassium permanganate is a very strong oxidizing agent and is useful as an oxidant in a wide spectrum of chemical reactions.
  • The Molecular Weight/ Molar Mass of Potassium permanganate is 158.034 g/mol.
  • The density of Potassium permanganate is \(2.703 g/cm^3\).
  • Also, the storage temperature of Potassium permanganate is room temperature.
  • The boiling point of potassium permanganate is \(100^oC\) and the melting point of potassium permanganate is \(240^oC\).
  • The oxidation state of potassium permanganate is +7.

FAQs on \(KMnO_4\)

Question 1: Explain the structure of potassium permanganate.

Answer: \(KMnO_4\) forms orthorhombic crystals with constants as a = 910.5 pm, b = 572.0 pm, c = 742.5 pm. The overall motif resembles that for barium sulfate, with which it gives solid solutions. In the solid, as in solution, each \(MnO_4^-\) ion centres are tetrahedral in geometry. The Mn–O distances are 1.62 Armstrong.

Question 2:  What are the uses of potassium permanganate?

Answer: Common uses of potassium permanganate are-

  • In a concentrated form, \(KMnO_4\) is an irritant to human eyes and skin and can react with many reducing agents or organic material but it is inflammable.
  • The antibacterial action of \(KMnO_4\) is according to the oxidation of proteins of bacteria or tissues by this compound. It leaves a stain on skin or tissues.
  • Potassium paramagnet acts as an antidote. A ratio of 1:5000 of permanganate solution when in use as a gastric wash oxidizes poison.
  • Potassium permanganate is stored in tightly closed containers and should be handled with care as an explosion may occur when it comes in contact with readily oxidizable substances.
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