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IODINE

Iodine ia a halogen element belonging to the group VII of the periodic table. It is a black dark violet shining solid, with a metallic lusture. It is characterised by

1. Atomic number 53
2. Relative atomic mass 126.9045
3. Relative density 4.94
4. Melting point 113.5^OC
5. Boiling point 183.45^OC
6. Iodine is insoluble in water but soluble in inorganic solvents.

PREPARATION

1. In the laboratory iodine can be prepared by the following reactions

• 2KI + Cl₂

è 2KCl + I₂

• CuSO₄ + 2KI

è CuI₂ + K₂SO₄

• NaIO₃ + 5NaI + 6H₂SO₄

è 6NaHSO₄ + 3H₂O + 3I₂

1. Commercially it is prepared from Chile salt-petre ( basically NaNO₃ in which small quantities of NalO₃ are present).

2NaIO₃+ 5NaHSO₃ è 3NaHSO₄ + 2Na₂SO₄ + H₂O+ I₂

 NOTE: If NaHSO₃ is present in excess then HI is produced

NaHSO₃ + I₂ + H2O è NaHSO₄ + 2HI

CHEMICAL PROPERTIES

1. Oxidising properties

H₂S + I₂ è 2HI + S

Na₂SO₃ + I₂ + H₂O è H₂SO₄ + 2HI

2. Iodine directly combines with elements

H₂+ I₂ è 2HI

2P + 3I₂ è 2PI₃

3. Reaction with alkalies

In cold

NaOH + I₂ è NaI + HIO

When heated

6NaOH + 3I₂ è 5NaI + NaIO₃ + 3H₂O

USES

1. Iodine is used in the manufacture of various iodine compounds ( iodoform, iodides etc.)
2. It is widely used in the medical field ( tincture of iodine)
3. It finds its uses in analytical chemistry.

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