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
aqueous neutral
aqueous acidic
both aqueous acidic and neutral
both aqueous acidic and faintly alkaline
The Correct Option is A
Solution and Explanation
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.
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