0.1 n Sodium thiosulfate Preparation and Standardization

0.1 n Sodium thiosulfate Preparation and Standardization
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0.1 n Sodium thiosulfate Preparation and Standardization

                       Preparation                 

Take 25 g of sodium thiosulfate pentahydrate (Na2S2O3·5H2O) in 500 mL of freshly boiled and cooled water, and add 0.11 g of sodium carbonate (Na2CO3).Dilute to 1 L with freshly boiled and cooled water, and let stand for 24 h. Store the solution in a tightly closed glass bottle.

                     Standardization            

Take 1 g of primary standard potassium dichromate (K2Cr2O7), transfer to a platinum dish, and dry at 120°C for 4 h. Cool in a desiccator.
Weigh accurately 0.21g of the dried K2Cr2O7, and transfer to a 500-mL glass-stoppered conical flask. Add 100 mL of water, swirl to dissolve, remove the stopper, and quickly add 3 g of potassium iodide (KI), 2 g of sodium bicarbonate (NaHCO3), and 5 mL of hydrochloric acid (HCl). Stopper the flask quickly, swirl to ensure mixing,and let stand in the dark for 10 min. Rinse the stopper and inner walls of the flask with water and titrate with the Na2S2O3 solution until the solution is yellowish green. Add 2 mL of starch solution (10 g/L), and continue the titration to the disappearance of the blue color.

                     Calculation                    

Normality of Na2S2O3 solution

   N = W/0.04904*V


  where:
N  = normality of the Na2S2O3 solution,
W = grams of K2Cr2O7 used, and
 V = millilitres of Na2S2O3 solution required for titration of
         the solution.

Ex-
0.2105 grams of K2Cr2O7 used, and
43.6 of Na2S2O3 solution.

N = 0.2105/0.04904*43.6
    = 0.09845 N

                         Stability                      

Re-standardize weekly





0.1 n Sodium thiosulfate Preparation and Standardization



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