Question

Peroxodisulphate salts (e.g., $N{a}_2{S}_2{O}_8$) are strong oxidizing agents used as
bleaching agents for fats, oils, etc.

Given :

$O_2\left(g\right)+4H^{\oplus }\left(aq\right)+4e^{-}\to 2H_{2}O\left(l\right)$

$E^{\ominus }=1.23V$

$S_2{O}_8^{2-}\left(aq\right)+2e^{-}\to S{O}_4^{2-}\left(aq\right)$

$E^{\ominus }=2.01V$

Which of the following statements is (are) correct ?

• A. Oxygen gas can oxidize sulphate ion to per-oxo disulphate ion $\left(S_2{O}_8^{2-}\right)$ in acidic solution.
• B. $O_2\left(g\right)$ is reduced to water.
• C. Water is oxidized to $O_2$.
• D. $S_2{O}_8^{2-}$ ions are reduced to $S{O}_4^{2-}$ ions.

Answer 1

Answer: (C), (D)

The correct options are
C Water is oxidized to $O_2$.
D $S_2{O}_8^{2-}$ ions are reduced to $S{O}_4^{2-}$ ions.

For the cell reaction :$O_2+S{O}_4^{2-}\to S_2{O}_8^{2-}+H_{2}O;E_{cell}^{\ominus }=1.23-2.<0$

Hence the reaction non-spontaneous in forward direction.

Hence the reverse reaction will be spontaneous.

So the correct cell reaction is :

$H_{2}O+S_2{O}_8^{2-}\to O_2+S{O}_4^{2-}$

Using the above reaction, option C and D are correct.