D-Block and F-Block Elements: Conversion of Pyrolusite into Potassium Manganate (For CBSE, ICSE, IAS, NET, NRA 2022)

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Potassium Permanganate

  • Pyrolusite ore is the starting material for the manufacture of potassium permanganate.
  • Pyrolusite is first converted into potassium manganate which is oxidized to potassium permanganate.

Conversion of Pyrolusite into Potassium Manganate

Pyrolusite is fused with hydroxide of sodium or potassium in the presence of air. manganite first formed is converted into a dark green mass of corresponding manganate as follows:

Potassium manganite

Potassium manganate

The dark green mass of potassium manganate is dissolved in a small quantity of cold water to form a dark green solution from which dark green crystals of potassium manganate may be obtained on concentration.

Conversion of Potassium Manganate to Potassium Permanganate

Potassium manganate may be converted into potassium permanganate by oxidation either chemically with chlorine or ozone or electrolytically at the anode.

Anodic oxidation

Physical Properties

  • Potassium permanganate forms dark purple red rhombic prisms.
  • It is sparingly soluble in water giving a deep purple colored solution which is opaque until very dilute.
  • The crystal on heating evolve oxygen and a black powder of potassium manganate and manganese dioxide.

Chemical Properties

Potassium permanganate is a powerful oxidizing agent.

The action in acidic, neutral and alkaline solutions are as follows:

In acidic solution, two molecules of permanganate furnish five atoms of oxygen as follows

Ferrous sulphate is oxidized to ferric sulphate by acidified potassium Permanganate.

In neutral solution the main reaction is:

oxidizes salts to and to and as follows:

In alkaline solutions the main reaction is:

Alkaline permanganate oxidizes iodides to iodates:

Uses

  • Potassium permanganate is used as an oxidizing agent in the laboratory and in industry.
  • It is used for disinfecting wells and lake water, as mouthwash, for washing wounds and gargling during throat infections.
  • It is used as a reagent in volumetric analyses for estimating Fe (II) ion, oxalic acid, oxalate ion, Sulphide and hydrogen peroxide.

F-Block Elements (Lanthanoids)

  • The two rows of elements shown separately at the periodic table contains f-Block elements.
  • The elements from are called lanthanoids.

Electronic Configuration

  • Lanthanum is the first member of the third transition series and has one two and two electrons.
  • Cerium retaining two electrons, has two electrons in the orbitals and none in the orbitals.
  • The atoms of the elements from cerium to lutetium have two to fourteen electron in their -orbitals.
  • Lanthanum does not possess any electrons, but it is placed with other element as a customary basis.
  • The filling up of the orbitals is regular with some exceptions is shown in table.

Electronic Configuration of Lanthanides

Electronic Configuration of Lanthanides

Lanthanoids Contraction

  • The regular decrease in atomic radii with increase in atomic number in the lanthanoids is known as lanthanide contraction.
  • This is because each succeeding lanthanide differs from its immediate predecessor in having one more electron in the orbitals and one extra proton in the nucleus of the atom.
  • electron constitute the inner shells and are rather ineffective in screening the nucleus.
  • Thus, there is a gradual increase in the attraction of the nucleus for the peripheral electrons as the nuclear charge increase.
  • This leads to a decrease in the atomic radii.

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