Preparation and Standardization of 0.05 M Iodine

Iodine Solution Preparation

• Dissolve about 14 g of iodine in a solution of 36 g of potassium iodide in 100 ml of water.
• Add three drops of hydrochloric acid and dilute with water to 1000 ml.
• Standardize the solution in the following manner.

Iodine Solution Standardization

• Weigh accurately about 0.15 g of arsenic trioxide, previously dried at 105° for 1 hour.
• Dissolve in 20 ml of 1M sodium hydroxide by warming, if necessary.
• Dilute with 40 ml of water, add 0.1 ml of methyl orange solution and add dropwise dilute hydrochloric acid until the yellow color is changed to pink.
• Add 2 g of sodium carbonate, dilute with 50 ml of water and add 3 ml of starch solution.
• Titrate with the iodine solution until a permanent blue color is produced.
• Store in amber-colored, glass-stoppered bottles.
• 1 ml of 0.05 M iodine is equivalent to 0.004946 g of As2O3.
• Calculate the molarity of solution by the following formula:

            As2O3 in mg
M = ----------------------------
         Iodine in ml x 4.946
Also see: Determination of Shelf Life of Solutions in Laboratory