SOP FOR PREPARATION AND STANDARDIZATION OF 0.1M SODIUM THIOSULPHATE

Preparation
Dissolve 25 g of sodium thiosulphate and 0.2 g of sodium carbonate in sufficient carbon dioxide-free water to produce 1000 ml.
Standardisation
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.
Perform a duplicate and calculate the molarity factor (MF)
Note down the average value
Calculation
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Note:
1) Restandardise before use
2) Discard the solution after 30 days.
3) For storage and labeling follow the general procedure.