Method for Preparation and Standardization of 0.1 (N) Sodium Thiosulphate Solution

 

Ø  Apparatus:-

·         250 ml Iodine flask

·         100 ml cylinder

·         50 ml burette

Ø  Reagents:-

·         Sodium Thiosulphate

·         Starch Indicator

·         Potassium dichromate (A.R. Grade)

·         Potassium Iodide (A.R Grade)

·         Hydrochloric Acid (A.R Grade)

Ø  Preparation of Solution:-

·         0.1 (N) Sodium Thiosulphate:- 

Weight accurately 25 g Sodium Thiosulphate and about 0.2 g Sodium Carbonate. Dissolve in 1000 ml DM water.

·         Starch Indicator:-

Dissolve 0.1 g Starch in 100 ml by heating.

Ø  Procedure:-

Take accurately about 0.1 g of primary standard Potassium Dichromate, previously dried at 120°C for 4 hours. Dissolve in 100 ml of DM water 500 ml Iodine flask. Swirl to dissolve the solid, remove the stopper and quickly add 3 g Potassium Iodide and 5 ml Hydrochloric Acid. Insert the stopper and swirl to mix. Then allow to stand in dark for 30 minutes. Then rinse the stopper and the inner wall with DM water. Then 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:-

                

Notes:- 1. Molecular Weight of Potassium Dichromate (K₂Cr₂O₇) = 294.185 g/mol