How do you make 0.1 M sodium thiosulphate solution?

Sodium Thiosulphate (0.1M) 

Molecular formula: Na2S2O3 

Molecular weight: 158.11 

Preparation: Dissolve 25 g of sodium thiosulphate and 0.2 g of sodium carbonate in carbon dioxide-free water and dilute to 1000 mL with the same solvent. 

Standardization: Dissolve 0.2 g of potassium bromate, weighed accurately, in sufficient water to produce 250 mL. To 50.0 mL of this solution add 2 g of potassium iodide and 3 mL of 2 M hydrochloric acid and titrate with the sodium thiosulphate solution using the starch solution, added towards the end of the titration, as an indicator until the blue color is discharged [I2 forms a blue colored complex with starch]. Re-standardize the solution frequently. 


KBrO3 + HI → HIO3 + KBr 

IO3 + 5I + 6H+ → 3I2 + 3H2

3[2Na2S2O3 + I2 → Na2S4O6 + 2NaI] 

Factor Calculation: 


6Na2S2O3 ≅ 3I2 ≅ HIO3 ≅ KBrO3 

6 moles of Na2S2O3 ≅ 1 mole of KBrO3 

6000 mL of 1M Na2S2O3 ≅ 167 g of KBrO3 

1 mL of 0.1M Na2S2O3 ≅ 0.002783 g of KBrO3

Make sure you also check our other amazing Article on: How do you prepare potassium permanganate?
Sharing Is Caring:

Leave a Comment