Iodine Volumetric Solution Preparation and Standardization

Iodine Volumetric Solution Preparation and Standardization (0.1 N) as per USP:

Preparation of Reagent:

Starch TS: Mix 1 gm of soluble starch with 10 mg of red mercuric iodide and a sufficient amount of cold water to make a thin paste. Add 2 ml of boiling water, and boil for 1 min with continuous stirring. Cool, and use only a clear solution.

1N Hydrochloric Acid: Dilute 85ml of Hydrochloric acid into 1000ml of water.

Sodium Thiosulfate VS (0.1 N): Dissolve about 26gm of sodium thiosulfate and 200mg of sodium carbonate in 1000ml of recently boiled and cooled water.

Iodine Volumetric Solution Preparation (0.1 N):

Dissolve about 14gm of Iodine in a solution of 36gm of Potassium Iodide in 100ml of water, add 3 drops of Hydrochloric acid, and dilute with water to 1000 ml.

For lower strength refer to the given table:

Strength of VS	Quantity of Iodine to be taken (g)	Quantity of Potassium Iodide to be taken (g)	Makeup with water (ml)
0.01 N	1.4	3.6	1000
0.05 N	6.5	18	1000

Standardization of Iodine Volumetric Solution (0.1 N):

1. Transfer 25ml of the Iodine solution into a 250ml of volumetric flask.
2. Dilute to volume with water to 100ml.
3. Add 1ml of 1N hydrochloric acid.
4. Swirl gently to mix.
5. Titrate with 0.1 N Sodium thiosulfate VS until the solution has a pale yellow color.
6. Add 2 ml of starch TS.
7. Continue the titration until the solution turns colorless.

Calculation formula of Iodine Volumetric Solution (0.1N):

• N x V
• Normality of Iodine = —————
• I

Where,

• N= Normality of Sodium Thiosulfate VS,
• V= Volume of Sodium Thiosulfate consumed,
• I= Volume of Iodine solution taken for titration

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