During an iodometric titration, sodium thiosulphate ( ) is used to titrate liberated in the presence — Redox Reactions and Volumetric Analysis Chemistry Question

💡 Solution & Explanation

The reaction is $2S_2O_3^{2-} + I_2 \rightarrow S_4O_6^{2-} + 2I^-$ . The average oxidation state of S in thiosulphate is +2, and in tetrathionate it is +2.5. Change per sulphur atom is 0.5. Since there are 2 sulphur atoms per $S_2O_3^{2-}$ ion, the n-factor is $0.5 \times 2 = 1$ . Thus, $E = M/1$ .