Method for Preparation and Standardization of 0.1 (N) Iodine Solution

 Ø  Apparatus:-

·         250 ml Iodine flask

·         100 ml Cylinder

·         50 ml Burette

·         1000 ml Volumetric Flask

·         250 ml Beaker

Ø  Reagents:-

·         Iodine Resublimed

·         Starch Indicator

·         Arsenic Trioxide (A.R. Grade)

·         Potassium Iodide (A.R Grade)

·         Hydrochloric Acid (A.R Grade)

Ø  Preparation of Solution:-

·         0.1 (N) Iodine Solution:- 

Weight accurately 14 g Iodine Resublimed in a 1000 ml volumetric flask and keep close with stopper. Then take accurately 36 g Potassium Iodide in 250 ml beaker and dissolve it in 100 ml DM water. Add the Potassium Iodide Solution along with 0.1 ml Hydrochloric Acid (A.R. Grade) to the 1000 ml volumetric flask and mix very well until complete dissolution. Then make up the volume up to 1000 ml with DM water. Then mix very well. Store it in amber coloured stopper bottle protected from light.

·         Starch Indicator:-

Dissolve 0.1 g Starch in 100 ml by heating.

Ø  Procedure:-

Take accurately about 0.1 g of primary standard Arsenic Trioxide, previously dried at 120°C for 4 hours. Dissolve in 20 ml of 1 (N) Sodium Hydroxide by warming, if necessary. Dilute with 40 ml of DM water. Add 0.1 ml methyl orange indicator and add drop wise dilute Hydrochloric Acid until the yellow colour is changed to pink. Add 2 g Sodium Carbonate and dilute with 50 ml DM water. Add 3 ml starch solution. Titrate with the 0.1 (N) iodine solution until a permanent blue colour is produced.

Ø  Calculation:-

v Notes:-

o   Molecular weight of Arsenic Trioxide is 197.841 g/mol.

o   This is a four electron transfer system.

o   As₂O₃  + 5 H₂O + 2 I₂ = 2 H₃AsO₄ + 4 HI