Potassium Permanganate and Potassium Dichromate

An oxidizing agent (also known as an oxidizer or an oxidant) is a chemical species that tend to oxidize other substances, causing the oxidation state of the material to rise by causing it to lose electrons. Halogens (such as chlorine and fluorine), oxygen, and hydrogen peroxide are examples of oxidizing agents.

Because oxidizing agents are generally found at their maximum potential oxidation states, they have a strong proclivity to acquire electrons and undergo reduction. Ions, atoms, and molecules with a high affinity for electrons are regarded as excellent oxidizers. The higher the electron affinity, the more powerful the oxidizing power.

Potassium permanganate and potassium dichromate are two strong oxidizing agents.

Potassium permanganate, commonly known as potash permanganate, has the chemical formula KMnO4. It’s made from the mineral pyrolusite. Potassium Permanganate is an odourless solid that resembles dark purple or bronze-coloured crystals. K2Cr2O7 is the chemical formula for potassium dichromate. Chromite ore is used to make K2Cr2O7. It is a crystalline substance that is red-orange in colour.

Potassium Permanganate

The following stages are involved in the preparation of KMnO4:

• MnO2 to potassium manganate conversion: In the presence of air, powdered pyrolusite is fused with potassium hydroxide to generate potassium manganate, a green chemical.

2MnO₂ + 4KOH + O₂ → 2K₂MnO₄ + 2H₂O

• Potassium manganate oxidation to potassium permanganate: There are two techniques for oxidation. There are two types of oxidation: chemical oxidation and electrolytic oxidation.

Chemical oxidation: Potassium permanganate is formed by treating potassium manganate with chlorine or ozone.

2K₂MnO₄ + Cl₂ →2KMnO₄ +2KCl

2K₂MnO₄ + H₂O+O₃ →2KMnO₄ +2KOH+O₂

Electrolytic oxidation: The potassium manganate solution is electrolyzed in this manner.

K₂MnO₄ ⇔2K⁺+MNO^2-₄

H₂O⇔H++OH^–

• Manganate ions are transformed into permanganate during this process.

MnO₄^2-→MnO₄^–+e^–

The green colour solution transforms to a purple colour solution after oxidation, which is concentrated by evaporation and forms crystals upon cooling.

Structure

Potassium permanganate is an ionic compound made up of a potassium cation (K⁺) and the permanganate anion (MnO₄^–). The manganese atom in the permanganate anion is connected to four oxygen atoms through three double bonds and one single bond. Manganese’s oxidation state in this salt is +7. Solid KMnO₄ has an orthorhombic crystal structure. Each (MnO₄^–) structure has a tetrahedral geometry.

Properties

• When potassium permanganate is heated, potassium manganate, manganese dioxide, and oxygen are produced.

2KMnO₄→ K₂MnO₄ +MnO₂+ O₂

• In acidic or alkaline solutions, it is a potent oxidizing agent.
• It takes the shape of purple crystals and dissolves in hot water.
• It is noncombustible, yet it acts as a catalyst in the combustion of combustible elements.
• When combined with glycerine, it will ignite.
• In large concentrations, it can become poisonous.
• It is a powerful oxidizing agent (a chemical that quickly transfers oxygen to other molecules), resulting in the formation of dark brown manganese dioxide, which stains anything organic. It is easily able to receive electrons from other compounds.
• It explodes when it comes into contact with sulfuric acid.
• It instantly interacts with glycerol and simple alcohols, creating flame and smoke.

Potassium Dichromate

Preparation

Potassium dichromate is a widely used chemical in the industry as an oxidising agent and in the synthesis of a variety of other chemicals.

Dichromates are often made from chromates, which are made by combining chromite ore with sodium/potassium carbonate in the presence of air.

• Sodium Chromate Preparation: In a reverberatory furnace, finely powdered chromite ore is heated with sodium carbonate in the presence of air. Sodium chromate is formed as a result of this reaction.

4FeCr₂O₄ + 8Na₂CO₃ + 7O₂ → 8Na₂CrO₄ + 2Fe₂O₃ + 8CO₂

• Sodium chromate is converted into sodium dichromate: The sodium chromate produced in the preceding process is treated with strong sulfuric acid to produce sodium dichromate.

2Na₂CrO₄ + 2H⁺ → Na₂Cr₂O₇ + 2Na⁺ + H₂O

• Sodium dichromate to potassium dichromate conversion: Following the formation of sodium dichromate, potassium dichromate is created by treating it with KCl.

Na₂Cr₂O₇ + 2KCl → K₂Cr₂O₇ + 2NaCl

As a result, we eventually have orange crystals of potassium dichromate.

Structure

The chromate ion has a tetrahedral shape, but the dichromate ion is made up of two tetrahedra that share one corner and have a bond angle of 126° with the chromate ion. Potassium dichromate’s chemical/molecular formula is K2Cr2O7, and its molecular mass is 294.185 g/mol. Potassium dichromate is an ionic compound composed of two potassium ions and one negatively charged dichromate ion.

In dichromate ion, two hexagonal chromium ions have an oxidation state of +6 and are bound to three oxygen atoms each as well as a bridging oxygen atom.

Properties

• Potassium dichromate decomposes when heated to generate potassium chromate, chromic oxide, and oxygen.

4K₂Cr₂O₇ + 2CrO₃ + 3O_{2 ^→}4K₂CrO₄+ 2CrO₃ + 3O₂

• It is a strong oxidizing agent. It converts iodide to iodine.
• When an orange-red solution of K₂Cr₂O₇ combines with an alkali, a yellow solution is formed due to the creation of potassium chromate.
• The yellow hue of K₂CrO_4.
• turns to orange-red when acidified due to the reformation of K₂Cr₂O_7.
• The chemical features vivid red crystals and is used for dyeing, colouring, tanning, and other purposes.
• It can be used as an astringent, antiseptic, and caustic in medicine. When heated, it releases hazardous chromium fumes.
• It is a very caustic and powerful oxidising agent, and it is utilised in wood preservatives, pigment production, and photochemical processes.