Standardisation of sodium thiosulphate solutions

An approximately O.IM solution is prepared by dissolving about 25 g crystallised sodium thiosulphate in 1 L of water in a graduated flask. The solution is standardised by any of the methods described below. 

Before dealing with these, it is necessary to refer briefly to the stability of thiosulphate solutions. Solutions prepared with conductivity (equilibrium) water are perfectly stable. However, ordinary distilled water usually contains an excess of carbon dioxide this may cause a slow decomposition to take place with the formation of sulphur  

Moreover, decomposition may also be caused by bacterial action (e.g. Thiobacillus thioparus), particularly if the solution has been standing for some time. For these reasons, the following recommendations are made  

Prepare the solution with recently boiled distilled water. 

Add 3 drops of chloroform or 10mgL 1 of mercury(II) iodide these compounds improve the keeping qualities of the solution. 

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Potassium hydrogen phthalate Potassium hydrogen phthalate Potassium iodate Anhydrous sodium carbonate Zinc metal Standardisation of sodium hydroxide solution Standardisation of acetous perchloric acid Standardisation of sodium thiosulphate solution through generation of iodine Standardisation of hydrochloric acid Standardisation of EDTA solution... 

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