In the iodometric titration 2Na2S2O3 + I2 -> Na2S4O6 + 2NaI, the equivalent mass of sodium thiosulfate (molar mass 158 g/mol) is:

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In the iodometric titration $2 Na X_{2} S X_{2} O X_{3} + I X_{2} Na X_{2} S X_{4} O X_{6} + 2 NaI$ , the equivalent mass of sodium thiosulfate (molar mass 158 g/mol) is:

Each

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

loses one electron in forming

S X_{4} O X_{6} X^{2 -}

(two thiosulfate ions lose 2 e

^{-}

in total), so n-factor = 1. Equivalent mass = M/1 = 158 g/eq.