0.1 n Sodium thiosulfate Preparation and Standardization

0.1 n Sodium thiosulfate Preparation and Standardization

0.1 n Sodium thiosulfate



0.1 N Sodium Thiosulfate Preparation and Standardization

 Preparation of 0.1 N Sodium thiosulfate Solution               


  • Take 25 g of sodium thiosulfate pentahydrate (Na2S2O3·5H2O) in 500 mL of freshly boiled and cooled water
  • 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 of  0.1 N Sodium thiosulfate       

  • 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, 
  • Transfer to a 500-mL glass-stoppered conical flask. 
  • Add 100 mL of water, swirl to dissolve, remove the stopper,
  • 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.
            Initial point Color        
        
0.1 n Sodium thiosulfate solution
 
  End point color
0.1 n Sodium thiosulfate solution




 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




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