Thiosulphate is oxidised by iodine as 2S2O3^2- + I2 -> S4O6^2- + 2I-. Taking the molar mass of Na2S2O3 as 158 g mol^-1, its equivalent mass in this reaction is:

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Thiosulphate is oxidised by iodine as $2 S X_{2} O X_{3} X^{2 -} + I X_{2} S X_{4} O X_{6} X^{2 -} + 2 I X^{-}$ . Taking the molar mass of $Na X_{2} S X_{2} O X_{3}$ as $158 g mo l^{- 1}$ , its equivalent mass in this reaction is:

Two thiosulphate ions lose a total of 2 electrons, so one

S X_{2} O X_{3} X^{2 -}

loses 1 electron. n-factor

= 1

and equivalent mass

= 158/1 = 158