Question

The reduction of peroxydisulphate ion by I^– ion is expressed by $S_{2}O_{8}^{2–}$ + 3 I^–¾® $2SO_{4}^{2–}$ + $I_{3}^{–}$ If rate of disappearance of $I^{–}$ is 9/2 × 10^–3mol lit^–1 S^–1, what is the rate of formation of $SO_{4}^{2–}$ during same time?

• A. 10^–3mol/L^–1 S^–1
• B. 2 × 10^–3mol L^–1 S^–1
• C. 3 × 10^–3mol L^–1 S^–1
• D. 4 × 10^–3mol L^–1 S^–1

Answer 1

Answer: (C)

3 × 10^–3mol L^–1 S^–1

Answer 2

$\frac{1}{2}$ $\frac{d\lbrack SO_{4}^{2–}\rbrack}{dt}$ = $\frac{1}{3}$ $\left( –\frac{d\lbrack I^{–}\rbrack}{dt} \right)$

$\frac{1}{2}$ × $\frac{d\lbrack SO_{4}^{2–}\rbrack}{dt}$ = $\frac{1}{3}$ × $\frac{9}{2}$

\ $\frac{d\lbrack SO_{4}^{2–}\rbrack}{dt}$ = 3 mol lit^–1 S^–1