Sodium thiosulphate
Sodium thiosulfate

A white salt with the formula Na₂S₂O₃, which is also known as sodium hyposulphite.

The reaction of sodium thiosulfate with iodine, which occurs in the pH range 2 to 9, is a fast quantitative reaction.

It is used for quantitatively determining iodine liberated by the oxidation of iodide ions. The product of the reaction is sodium tetrathionate:

2S₂O₃^2- + I₂2 I^- + S₄O₆^2-

Note :
modern textbooks write "sulfate" but older ones write "sulphate".

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