Question

The reduction of peroxy disulphate ion by $I^{-}$ion is expressed by $S _{2} O _{8}^{2-}+3 I ^{-} \longrightarrow 2 SO _{4}^{2-}+ I _{3}^{-}$. If rate of disappearance of $I ^{-}$is $9 / 2 \times 10^{-3} mol \,lit ^{-1} s ^{-1}$, what is the rate of formation of $2 SO _{4}^{2-}$ during same time?

• A. $3 \times 10^{-3} \, mol \, Lit^{-1} \, s^{-1}$
• B. $2 \times 10^{-3} \, mol \, Lit^{-1} \, s^{-1}$
• C. $10^{-3} \, mol \, Lit^{-1} \, s^{-1}$
• D. $4 \times 10^{-3} \, mol \, Lit^{-1} \, s^{-1}$

Answer 1

Answer: (A)

$\frac{1}{2} \frac{d\left[S O_{4}^{2-}\right]}{d t}=\frac{1}{3}\left(-\frac{d\left(I^{-}\right)}{d t}\right)$
$\frac{1}{2} \times \frac{d\left[S O_{4}^{2-}\right]}{d t}=\frac{1}{3} \times \frac{9}{2} \times 10^{-3}$
$\therefore \frac{d\left[S O_{4}^{2}\right]}{d t}=3 \times 10^{-3} mol \,Lit ^{-1}\, s ^{-1}$