Question

When Manganeses (II) reacts with peroxodisulphate, the respective products obtained are:

• A. \(\text{MnO}_4^{2-}\) only
• B. \(\text{MnO}_4^-\) and \(\text{SO}_4^{2-}\)
• C. \(\text{MnO}_2\) and \(\text{S}_2\text{O}_4^{2-}\)
• D. \(\text{MnO}_4^{2-}\) and \(\text{SO}_4^{2-}\)

Hint:

Peroxodisulphate (\(\text{S}_2\text{O}_8^{2-}\)) is an exceptionally strong oxidant that oxidizes \(\text{Mn}^{2+}\) directly to permanganate (\(\text{MnO}_4^-\)), not stopping at \(\text{MnO}_4^{2-}\) or \(\text{MnO}_2\).

Answer 1

The Correct Option is B

Concept:
Peroxodisulphate (persulphate, \(\text{S}_2\text{O}_8^{2-}\)) is a very strong oxidizing agent in aqueous solution with a standard reduction potential of \(E^\circ = +2.01\text{ V}\).
It oxidizes lower oxidation states of transition metals to their highest stable oxidation states.

Step 1: Oxidation of Manganese(II):
In the presence of peroxodisulphate (typically catalyzed by silver ions, \(\text{Ag}^+\)), manganese(II) salts (\(\text{Mn}^{2+}\)) are oxidized to the intense purple permanganate ion (\(\text{MnO}_4^-\)), where manganese is in its highest oxidation state of \(+7\).

Step 2: Reduction of Peroxodisulphate:
The peroxodisulphate ion contains an unstable peroxo linkage (\(-\text{O}-\text{O}-\)) in which the oxygen atoms have an oxidation state of \(-1\).
During the redox process, the peroxo bond is reduced, converting the persulphate ion into two sulphate ions (\(\text{SO}_4^{2-}\)), where oxygen is in the normal \(-2\) oxidation state:
\[ \text{S}_2\text{O}_8^{2-} + 2e^- \rightarrow 2\text{SO}_4^{2-} \]

Step 3: Overall Stoichiometric Reaction:
Combining the oxidation and reduction half-reactions yields the overall balanced equation:
\[ 2\text{Mn}^{2+} + 5\text{S}_2\text{O}_8^{2-} + 8\text{H}_2\text{O} \rightarrow 2\text{MnO}_4^- + 10\text{SO}_4^{2-} + 16\text{H}^+ \] The products formed from this reaction are \(\text{MnO}_4^-\) (permanganate ion) and \(\text{SO}_4^{2-}\) (sulphate ion).
Final Answer:
The respective products obtained are \(\text{MnO}_4^-\) and \(\text{SO}_4^{2-}\), which corresponds to option (B).