IODINE SOLUTION, 0.1 N


              IODINE SOLUTION, 0.1 N            




                     Preparation                        

Take 12.7 g of iodine and 60 g of potassium iodide (KI) to an 800-mL beaker, add 30 mL of water, and stir until solutionis complete. Dilute with water to 500 mL, and filter through a sintered-glass filter. Wash the filter with about 15 mL of water, transfer the combined filtrate and washing to a 1-L
volumetric flask, dilute to the mark with water, and mix. Store the solution in a glass-stoppered, amber-glass bottle in a cool place.

Standardization

Transfer 1 g of primary standard arsenic trioxide (As2O3) to a platinum dish, and dry at 105°C for 1 h. Cool in a desiccator.
Weigh accurately 0.20 g of the dried As2O3 and transfer to a 500-mL conical flask. Add 10 mL of sodium hydroxide solution (NaOH, 40g/L), and swirl to dissolve. When solution is complete, add 100 mL of water and 10 mL of sulfuric acid (H2SO4, 1 + 35), and mix. Slowly add sodium bicarbonate (NaHCO3) until efferves-cence ceases, add 2 g of NaHCO3 in excess, and stir until dissolved. Add 2 mL of starch solution (10 g/L) and titrate with the iodine solution to the first permanent blue color.

*Warning—Arsenic trioxide is extremely toxic, avoid ingestion

                     Calculation                        

Normality of the iodine solutions

I = w /0.04946*v
where:
I= normality of the iodine solution,
w= grams of As2O3 used, and
V= millilitres of iodine solution required for titration of the solution.

Ex
0.2202 = grams of As2O3 used, and
44.8 = millilitres of iodine solution required for titration of the solution.
 I = 0.2202/0.04946*44.8
   = 0.0993 N




                          Stability                          

*Re-standardize sealed bottles monthly.
*Re-standardize open bottles weekly.

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