Question

in the reaction s2o3 2- +br- ----- > so4 2- +br- , the number of mols of thiosulphate oxidised by one mol br2 and equivalent mass of thiosulphate are respectively
1) i/2 , M/4
2) 1/4,M/4
3) 1/4 ,M/8
4) 1/8 ,M/8

Answer 1

The balanced chemical equation :

$S_{2}^{+2} O_{3}^{-2} +2Br_{2} +5H_{2}O\rightarrow 2SO_{4}^{-2} +4Br^{-} +10H^{+}$

From the balanced chemical equation⇒

1 mole of thiosulphate is oxidized by 2 moles of Br₂.

So, $\frac{1}{2}$ mole of thiosulphate is oxidized by 1 mole of Br₂.

Sulphur oxidation state changes from +2 in thiosulphate to +6 in sulphate.

$S_{2}^{+2} }O_{3} ^{-2} \rightarrow 2S^{+6} O_{4} ^{-2}$

N-factor is the change in oxidation number.

So, the n-factor for thiosulphate is 4.

Equivalent Mass= $\frac{Molar \ mass(M)}{n-factor}$

Equivalent Mass of thiosulphate=$\frac{M}{4}$

Hence, the correct option is 1)1/2, M/4.