Sodium Thiosulfate VS

Sodium Thiosulphate VS; Na₂S₂O₃,5H₂O = 248.2

For a 0.1m solution Dissolve 25 g of sodium thiosulfate and 0.2 g of sodium carbonate in carbon dioxide-free water and dilute to 1000.0 mL with the same solvent.

Standardisation. To 10.0 mL of 0.033 M potassium bromate, add 40 mL of water, 10 mL of potassium iodide solution and 5 mL of hydrochloric acid R1. Titrate with the sodium thiosulfate solution, using 1 mL of starch solution, added towards the end of the titration, as indicator.

1 mL of 0.1 M sodium thiosulfate is equivalent to 2.783 mg of KBrO₃ or 0.5 mL of 0.033 M potassium bromate.