Question

During the reaction of permanganate with thiosulphate, the change in oxidation of manganese occurs by value of 3. Identify which of the below medium will favour the reaction

• A. aqueous neutral
• B. aqueous acidic
• C. both aqueous acidic and neutral
• D. both aqueous acidic and faintly alkaline

Answer 1

The Correct Option is A

Permanganate Thiosulphate Reaction Conditions Analysis 

The reaction of permanganate \( (\text{MnO}_4^-) \) with thiosulphate \( (\text{S}_2\text{O}_3^{2-}) \) depends on the pH of the medium. Permanganate can be reduced to different manganese species depending on the conditions.

In a neutral or weakly alkaline medium, permanganate is reduced to manganese(IV) oxide \( (\text{MnO}_2) \):

\( \text{MnO}_4^-\text{(aq)} + 2\text{H}_2\text{O(l)} + 3e^- \rightarrow \text{MnO}_2\text{(s)} + 4\text{OH}^-\text{(aq)} \)

In this reaction, the oxidation state of manganese changes from +7 in \( \text{MnO}_4^- \) to +4 in \( \text{MnO}_2 \), a change of 3 units.

In an acidic medium, permanganate is reduced to manganese(II) ions \( (\text{Mn}^{2+}) \):

\( \text{MnO}_4^-\text{(aq)} + 8\text{H}^+\text{(aq)} + 5e^- \rightarrow \text{Mn}^{2+}\text{(aq)} + 4\text{H}_2\text{O(l)} \)

Here, the oxidation state of manganese changes from +7 to +2, a change of 5 units.

Conclusion:

Since the question specifies a change in oxidation state of 3, the reaction must be occurring in a neutral or weakly alkaline medium.