Determination of Sodium Hypophosphite Monohydrate Content

 Ø  Apparatus:-

·         250 ml iodine flask

·         100 ml cylinder

·         50 ml burette

·         10 ml graduated pipette

·         2 ml bulb pipette

Ø  Reagents:-

·         0.1 (N) Sodium Thiosulphate Solution

·         0.1 (N) Iodine Solution

·         Starch Indicator

·         6 (N) Hydrochloric Acid

Ø  Preparation of Solution:-

·         0.1 (N) Sodium Thiosulphate :- 

Weight accurately 25 g Sodium Thiosulphate (A.R Grade) and about 0.2 g Sodium Carbonate. Dissolve it in 1000 ml DM water.

·         Starch Indicator:-

Dissolve 0.1 g of Starch in 100 ml DM water by heating.

·         6 (N) Hydrochloric Acid:-

Take 50 ml DM water in a glass beaker and add 50 ml Hydrochloric Acid (A.R Grade) slowly. Then mix thoroughly by a glass rod.

·         0.1 (N) Iodine Solution:- Weigh 40 g of potassium iodide (KI) in a 500 mL glass-stoppered flask and dissolve in 100 mL of purified water. Let the solution come to room temperature, add 12.7 g of resublimed iodine (I₂ ), restopper the flask, and swirl the flask until the iodine is completely dissolved. Transfer the solution quantitatively to a 1 L volumetric flask, add 3 drops of hydrochloric acid (37% HCl; sp g 1.19) and dilute to 1 L with purified water. Mix thoroughly and transfer to a glass stoppered alkali-resistant, amber-colored bottle.

Ø  Procedure:-

         Take accurately 3 ml product in a 100 ml volumetric flask and add DM water up to 100 ml. Then mix thoroughly and take accurately 2 ml from 3% (v/v) solution to Iodine flask. Add approximately 25 ml 6 (N) Hydrochloric Acid. Then add accurately 25 ml 0.1 (N) standard Iodine solution. Rinse down the neck with 4 ml to 5 ml 6 (N) Hydrochloric Acid. Then close the Iodine flask with standard stopper and keep aside the flask in dark for 30 minutes.  Rinse the stopper and neck of the flask with a small amount of  DM water. Titrate immediately with 0.1 (N) Sodium Thiosulphate standard solution to a straw colour, then add about 0.5 ml starch indicator solution. Sample will turn dark blue. Continue titration to the disappearance of the blue colour.

Ø  Calculation:-

Sodium Hypophosphite mono hydrate content in percentage (w/v) =

8.83 × {Volume of 0.1 (N) Iodine added × factor - Volume of 0.1 (N) Sodium Thiosulphate × factor}

Ø  Notes:- Molecular weight of Sodium Hypophosphite mono hydrate is 105.99 g.