7.9 g of anhydrous Na2S2O3 (M=158 g mol^-1) is used as an antichlor and is oxidised completely to sulphate by chlorine (Cl- is the only chlorine product). Taking Cl=35.5, the mass of Cl2 consumed is

JEE Advanced levelSingle correct optionDifficulty 3 of 3ph101

$7.9 g$ of anhydrous $Na X_{2} S X_{2} O X_{3}$ ( $M = 158 g mo l^{- 1}$ ) is used as an antichlor and is oxidised completely to sulphate by chlorine ( $Cl X^{-}$ is the only chlorine product). Taking $Cl = 35.5$ , the mass of $Cl X_{2}$ consumed is

Moles of thiosulphate

= 7.9/158 = 0.05

. Each thiosulphate loses 8 electrons (

S

from +2 to +6 in both atoms) and each

Cl X_{2}

gains 2, so 4 mol

Cl X_{2}

per mol. Moles of

Cl X_{2} = 0.20

and mass

= 0.20 \times 71 = 14.2 g