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Table Of Content

What is Iodine?

Iodine is a chemical element of the Halogen family with atomic number 53. It is represented by symbol I. It exists as diatomic solid, I2(S).Iodine is an essential part of our diet deficiency of which cause Goiter.

Black Flakes of Iodine

Black Flakes of Iodine

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Commercial Methods of obtaining Iodine

From Chile saltpeter (NaNO3)

Chile saltpeter contains trace amount of Sodium Iodate (NaIO3) and Sodium Periodate (NaIO4) as impurity. An important property of Chile saltpeter is that it is soluble in water while its impurities are not .This property can be used to separate impurities from Chile saltpeter.

Sodium Iodate

Sodium Iodate

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The rock containing Chile saltpeter is crushed and dissolved in hot water which is allowed to cool for a while. On cooling Chile saltpeter crystallizes and can be separated from the residue (richer with Iodate ion) left in mother liquor.

This concentrated solution is now divided into two parts:

First part is allowed to react with Sodium bisulfite (NaHSO3) so as to reduce Iodate (IO3-) to Iodide (I-).

Reaction of Sodium bisulfite with Iodate to produce Iodide

This solution is added to unreacted second part so as to produce Iodine I2.

Reaction of Iodide with Iodate to produce Iodine

Solid Iodine obtained, can be separated out by filtration. It can be purified by sublimation process as Iodine crystals are sublimable.

Sublimation of Iodine

From sea water

Sea water contained Iodide (I-) which is oxidized by Chlorine to produce Iodine.

Reaction of Iodide with Chlorine to produce Iodine

Properties of Iodine

  • It exists as diatomic solid and crystallizes as black flakes and has a metallic luster.
  • It is a poor oxidizing agent in comparison to Fluorine, Chlorine and Bromine.
  • A solid crystal of Iodine conducts electricity .Their conductivity is directly proportional to temperature. Conductivity of Iodine increases with the rise in temperature. This property is due to self ionization of Iodine into cation Iodonium (I3+) and I3- ion.

Iodine molecule breaking to Iodonium and I3- ion at higher temperature

Uses of Iodine

It is used to synthesize many compounds which have unique commercial uses.

  1. Iodoform (CHI3) is used as an antiseptic.
  2. Silver Iodide (AgI) is used in photographic film.
  3. Sodium Iodide (NaI) small amount is added to table salt so as to make it iodized. If the salt is not iodized it may cause Goitre.
  4. Jincture Iodine (Iodine in Potassium Iodide (KI)) is used as an antiseptic.
  5. Nessler’s Reagent K2 [HgI4] is used as a laboratory reagent for detection of Ammonia.

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