• British Pharmacopoeia Volume IV
  • Appendices
  • Appendix I B. Volumetric Reagents and Solutions
  • Volumetric Solutions

Sodium Thiosulphate VS
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Sodium Thiosulphate VS Na2S2O3,5H2O = 248.2

For a 0.1m solution Dissolve 25  g of sodium thiosulphate and 0.2  g of sodium carbonate in sufficient carbon dioxide-free water to produce 1000  ml.

Ascertain its exact concentration in the following manner. To 20  ml of 0.0167m potassium bromate VS add 40  ml of water, 10  ml of potassium iodide solution and 5  ml of 7m hydrochloric acid. Titrate with the sodium thiosulphate solution using 1  ml of starch solution, added towards the end of the titration, as indicator. Each  ml of 0.1m sodium thiosulphate VS is equivalent to 2.784  mg of KBrO3.