Page 43 - Pharmaceutical Analytical Chemistry II - Pharm D Clinical- 07-PA202

V- Potassium Iodate, KIO3
Properties

- It is a primary standard oxidizing agent,
- Its aqueous solutions are stable indefinitely

Applications

Andrew´s method

- Determination of I− or I2 / I− (Iodine solution)

- Carried out in strongly acidic solutions> 4M HCl (for stability of
I+ as ICl or ICl2-)
- Ind. used, CCl4 or CHCl3

[1] Determination of I−.

Two steps reaction:

Step 1: IO3− + 5I− + 6H+ 3I2 + 3H2O
colorless Brown solution

Step 2: IO3− + 2I2 + 10Cl− + 6H+ 5ICl2− + 3H2O
Brown Yellow iodonium ion

Overall reaction:

IO3– + 2I– + 6Cl– + 6H+ ⎯⎯⎯→ 3ICl2– + 3H2O

Color change during titration:

Colorless (IO3− + I− ) to yellowish brown (I2 ) to dark brown (↑I2 )to
faint brown-yellow (↓ I2 , ↑ICl2− ) this is accompanied by fading of
pink color of CHCl3 layer, ep is indicated by disappearance of last
traces of I2 " CHCl3 layer is colorless"

[2] Determination of I2 / I- mixture

a) for total content:
Direct titration by st. IO3− , 5M HCl, CCl4 Ind.

IO3− + 2I2 + 10Cl− + 6H+ 5ICl2− + 3H2O
Brown Yellow

IO3– + 2I– + 6Cl– + 6H+ ⎯⎯⎯→ 3ICl2– + 3H2O

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